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Biomechanics of turning manoeuvres in Steller sea lions (Eumetopias jubatus) Cheneval, Olivier 2005

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B I O M E C H A N I C S O F T U R N I N G M A N O E U V R E S IN S T E L L E R S E A LIONS  {EUMETOPIAS JUBA TUS)  by OLIVIER CHENEVAL B . S c , Universite du Quebec a Montreal ( U Q A M ) , 1998  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF T H E REQUIREMENTS FOR THE DEGREE O F  MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES  Zoology  T H E UNIVERSITY OF BRITISH COLUMBIA May 2005  © Olivier Cheneval, 2005  II  ABSTRACT Otariids s u c h a s t h e Steller s e a lion  (Eumetopias jubatus)  are a m o n g the most manoeuvrable of  m a r i n e m a m m a l s ( e x p r e s s e d a s a m i n i m u m t u r n i n g radius a n d s p e e d d u r i n g m a n o e u v r e s ) . T h e y e v o l v e d in terrestrial a n d a q u a t i c e n v i r o n m e n t s t h a t a r e structurally c o m p l e x , a n d f e e d o n prey that are an order of magnitude smaller than themselves. C o m p a r e d to other aquatic organisms, Steller s e a lions h a v e a n u n s t a b l e b o d y d e s i g n a n d a r e p r e s u m e d to i n v o k e s w i m m i n g t e c h n i q u e s t h a t reflect t h e i r n e e d t o b e h i g h l y m a n o e u v r a b l e .  Detailed information was  experimentally  o b t a i n e d a b o u t t h e t u r n i n g t e c h n i q u e s e m p l o y e d by otariids t h r o u g h j o i n t l y a n a l y s i n g k i n e m a t i c a n d kinetic p a r a m e t e r s m e a s u r e d f r o m v i d e o r e c o r d i n g s o f t h r e e c a p t i v e S t e l l e r s e a lions. Centripetal  force  and  thrust  production  were  determined  by  examining  body  movements  throughout a series of turns. Results s h o w e d that most of the thrust w a s produced during the p o w e r p h a s e of t h e s t r o k e c y c l e of t h e pectoral f l i p p e r s . A s o p p o s e d t o p r e v i o u s f i n d i n g s , v e r y little or no t h r u s t w a s g e n e r a t e d d u r i n g initial a b d u c t i o n o f t h e p e c t o r a l f l i p p e r s a n d d u r i n g t h e final d r a g - b a s e d p a d d l i n g style o f t h e s t r o k e c y c l e . P e a k of t h e t h r u s t f o r c e w a s r e a c h e d h a l f w a y through  the  power  phase, while  the  centripetal  force  r e a c h e d its m a x i m u m  value at  the  b e g i n n i n g of t h e p o w e r p h a s e . K i n e m a t i c a s p e c t s of t h e m a n o e u v r e s c h a n g e d w i t h t h e t i g h t n e s s of t h e t u r n s a n d t h e initial v e l o c i t i e s . T h e d e g r e e o f d o r s a l f l e x i o n o f t h e b o d y c h a n g e d w i t h t h e t u r n i n g radius a n d t h e d e g r e e of flipper a b d u c t i o n v a r i e d w i t h s w i m m i n g s p e e d . H o w e v e r , t h e g e n e r a l m a n o e u v r i n g t e c h n i q u e a n d t u r n i n g s e q u e n c e r e m a i n e d t h e s a m e in all t h e r e c o r d e d m a n o e u v r e s . C o n t r a s t i n g t h e t u r n i n g p e r f o r m a n c e of t h e Steller s e a lion w i t h a s i m p l e d y n a m i c m o d e l of u n p o w e r e d m a n o e u v r e s in a q u a t i c a n i m a l s s h o w e d significant d e p a r t u r e s f r o m m o d e l predictions d u e to t h e h y d r o d y n a m i c effects o f b o d y m o v e m e n t s . O v e r a l l , t h e t u r n i n g s e q u e n c e of t h e Steller s e a lion w a s f o u n d to be v e r y c o n s i s t e n t , a n d t h e i r m a n o e u v r a b i l i t y w a s f o u n d t o c o m e f r o m their ability t o v a r y t h e d u r a t i o n a n d intensity o f m o v e m e n t s w i t h i n t h e sequence.  turning  iii  TABLE OF CONTENTS  ABSTRACT LIST O F TABLES LIST OF FIGURES ACKNOWLEDGEMENTS  II IV V VI  INTRODUCTION  1  MATERIALS AND METHODS  4  Morphology  4  Experimental set-up  10  Video analysis  12  RESULTS  16  Morphology  16  Kinematics  19  Kinetics  26  DISCUSSION  32  Morphology  32  Kinematic analysis  37  Kinetic a n a l y s i s  48  CONCLUSIONS  54  REFERENCES  56  iv  LIST OF TABLES  T a b l e 1:  M a s s of t h e t h r e e f e m a l e Steller s e a lions o n t h e d a y o f t h e f i l m e d trials  17  Table 2:  M o r p h o l o g i c a l d a t a of t h e t h r e e f e m a l e Steller s e a lions  18  Table 3:  S e q u e n c e o f m o v e m e n t s p e r f o r m e d by S L 3 d u r i n g a 180 d e g r e e s t u r n  23  T a b l e 3 ( c o n t i n u e d ) : S e q u e n c e of m o v e m e n t s p e r f o r m e d by S L 1 a n d S L 2 d u r i n g a 180 degrees turn  24  Table 4:  31  M e a n kinetic p a r a m e t e r s for t h e S L 3 , S L 2 , a n d S L 1  V  LIST OF FIGURES  Fig. 1:  3-D r e p r e s e n t a t i o n o f t h e b o d y o f S L 3 a s o b t a i n e d f r o m girth m e a s u r e m e n t s  5  Fig. 2 :  Lifetime v a r i a t i o n of 4 girth m e a s u r e m e n t s as a f u n c t i o n of b o d y m a s s  7  Fig. 3 :  O n - s c r e e n m o r p h o l o g i c a l m e a s u r e m e n t s of t h e left p e c t o r a l flipper of S L 3  9  Fig. 4 :  O n - s c r e e n m o r p h o l o g i c a l m e a s u r e m e n t s of t h e left pelvic flipper o f S L 3  9  Fig. 5 :  Schematic of the experimental set-up  11  Fig. 6 :  S e q u e n c e o f m o v e m e n t s b a s e d o n t u r n H 1 2 8 p e r f o r m e d by S L 3  22  Fig. 7:  R e l a t i o n s h i p b e t w e e n t u r n i n g radius a n d t h e d e g r e e o f b o d y c u r v a t u r e o f t h r e e Steller s e a lions p e r f o r m i n g a 180 d e g r e e s t u r n  Fig. 8 :  25  T r a j e c t o r y a n d s p e e d profile of t h e s h o u l d e r , c e n t r e o f g r a v i t y , a n d hip m a r k e r s o f a S t e l l e r s e a lion p e r f o r m i n g a 180 d e g r e e s t u r n  Fig. 9 :  Fig. 10:  Fig. 1 1 :  T a n g e n t i a l a n d n o r m a l a c c e l e r a t i o n profiles o f t h e s h o u l d e r , t h e c e n t r e g r a v i t y , a n d hip m a r k e r s of a Steller s e a lion p e r f o r m i n g a 180 d e g r e e s t u r n  29 of  T r a j e c t o r y o f t h e n o s e a n d s h o u l d e r o f a s e a lion p e r f o r m i n g a 1 8 0 d e g r e e s turn  45  C o m p a r i s o n o f t h e s p e e d profiles of t h e s h o u l d e r , c e n t r e o f g r a v i t y , a n d hip m a r k e r s o f a Steller s e a lion p e r f o r m i n g a f a s t a n d a s l o w 180 d e g r e e s t u r n  Fig. 1 3 :  44  C o m p a r i s o n of t h e s p e e d profiles o f t h e s h o u l d e r , c e n t r e of g r a v i t y , a n d hip markers with the predictions of a theoretical model  Fig. 12:  30  46  R e l a t i v e t u r n i n g radius a n d a v e r a g e t u r n i n g s p e e d o f t h r e e S t e l l e r s e a lions in c o m p a r i s o n t o California s e a lions  47  vi  ACKNOWLEDGEMENTS I w o u l d like to a c k n o w l e d g e m y thesis a d v i s o r s , Dr. A n d r e w W . T r i t e s a n d D r . R o b e r t W . B l a k e for their s u p p o r t d u r i n g this project. Dr. R o b e r t W . B l a k e w a s e x t r e m e l y helpful a n d s u p p o r t i v e during  the  analysis and  provided  me  with  lab  s p a c e . Dr.  David  A.  S. R o s e n w a s  very  a c c o m m o d a t i n g o f m y r e s e a r c h n e e d s at t h e V a n c o u v e r A q u a r i u m .  I w o u l d like t o a c k n o w l e d g e t h e V a n c o u v e r A q u a r i u m f o r p r o v i d i n g r e s e a r c h facilities a n d t h e staff for t h e i r help. I e s p e c i a l l y w a n t to t h a n k t h e Steller t e a m at t h e V a n c o u v e r A q u a r i u m : R e b e c c a Barrick a n d C h a d N o r d s t r o m , a s well a s the s e a lion t r a i n e r s : S h a w n C a r r i e r , A n d r e w I r v i n e , Billy L a s b y , V a n c e M e r c e r , T r o y N e a l e , Nigel W a l l e r , a n d G w y n e t h S h e p h a r d for  their  p r e c i o u s help a n d s u p p o r t . T h a n k s also t o all t h e staff, c o l l e a g u e s a n d f e l l o w s t u d e n t s in t h e M a r i n e M a m m a l R e s e a r c h Unit w h o p r o v i d e d help o n f r e q u e n t funded  by  NSERC,  and  grants  to  the  North  basis. This w o r k w a s  Pacific Universities  Marine  Mammal  partially Research  C o n s o r t i u m f r o m N O A A a n d t h e North Pacific M a r i n e S c i e n c e F o u n d a t i o n .  Lastly, I w o u l d like t o a c k n o w l e d g e m y f a m i l y a n d f r i e n d s . I a m e s p e c i a l l y g r a t e f u l t o m y p a r e n t s for their c o n t i n u a l s u p p o r t a n d e n c o u r a g e m e n t .  1  INTRODUCTION Most studies on the locomotion of aquatic animals have focused o n fast-start  responses or on  p e r f o r m a n c e d u r i n g s t e a d y s w i m m i n g ( s e e B l a k e , 2 0 0 4 for a n e x t e n s i v e r e v i e w ; D o m e n i c i a n d B l a k e , 1 9 9 7 ; Firth a n d B l a k e , 1 9 9 1 ; H a r p e r a n d B l a k e , 1 9 9 0 ; W a r d l e , 1 9 7 5 ; W e b b , 1 9 7 7 ; W e b b , 1 9 7 8 ; Weihs,  1 9 7 3 ) . C o m p a r a t i v e l y , little r e s e a r c h has b e e n d o n e o n t h e  manoeuvrability  of  aquatic  o r g a n i s m s — w h i c h N o r b e r g a n d R a y n e r ( 1 9 8 7 ) d e f i n e d a s t h e ability t o t u r n in a c o n f i n e d s p a c e ( G e r s t n e r , 1 9 9 9 ; S c h r a n k e t a l . , 1 9 9 9 ; W a l k e r , 2 0 0 0 ; W e b b , 1 9 8 3 ) . Y e t , t h e m a j o r i t y of a q u a t i c a n i m a l s rarely s w i m in a s t e a d y linear f a s h i o n e s p e c i a l l y in c o a s t a l e n v i r o n m e n t s t h a t a r e o f t e n structurally  c o m p l e x . O r g a n i s m s in c o a s t a l e n v i r o n m e n t s  constantly  need to manoeuvre and  to  a d j u s t their t r a j e c t o r i e s in t h e f a c e of d e s t a b i l i s i n g c u r r e n t s o r t o a v o i d o b s t a c l e s . M a n o e u v r a b i l i t y is also a key c o m p o n e n t o f p r e d a t o r - p r e y interactions in t h e a q u a t i c e n v i r o n m e n t w h e r e p r e d a t o r s a r e often s u b s t a n t i a l l y larger a n d f a s t e r t h a n their prey ( H o w l a n d , 1 9 7 4 ) .  In t h e c a s e o f m a r i n e m a m m a l s , a n d e s p e c i a l l y p i n n i p e d s , t h e m a j o r i t y o f kinetic s t u d i e s h a v e concentrated on measuring drag, functional design, and m a x i m u m  linear s p e e d ( D o m e n i c i  and  B l a k e , 2 0 0 0 ; E n g l i s h , 1 9 7 6 ; F e l d k a m p , 1 9 8 7 b ; F i s h , 1 9 9 3 ; Fish e t a l . , 1 9 8 8 ; P o n g a n i s e t a l . , 1 9 9 0 ; Stelle  et  al.,  2000;  Williams  and  Kooyman,  1985).  Few  have  considered  the  swimming  m a n o e u v r a b i l i t y of m a r i n e m a m m a l s (Fish et a l . , 2 0 0 3 ; G e r s t n e r , 1 9 9 9 ; M a r e s h et a l . , 2 0 0 4 ; S c h r a n k et a l . , 1999; Walker, 2 0 0 0 ; W e b b , 1983).  In a s e r i e s o f r e c e n t p a p e r s , W e i h s ( 2 0 0 2 ) a n d Fish ( 2 0 0 2 ) d i s c u s s e d t h e d i r e c t conflict  between  m a n o e u v r a b i l i t y a n d stability in a q u a t i c l o c o m o t i o n a n d its effect o n t h e f u n c t i o n a l d e s i g n o f active a q u a t i c o r g a n i s m s . B y d e f i n i t i o n , a m a n o e u v r e is a c h a n g e o f t r a j e c t o r y o r v e l o c i t y c a u s e d b y a linear o r rotational a c c e l e r a t i o n . In o t h e r w o r d s , it is a c o n t r o l l e d instability d u r i n g w h i c h t h e s u m of all f o r c e s a n d m o m e n t s o f f o r c e a c t i n g o n t h e c e n t r e o f gravity o f t h e a n i m a l d o not e q u a l z e r o . T h i s c r e a t i o n o f u n b a l a n c e d f o r c e s is theoretically p r o m o t e d by m o r p h o l o g i c a l c h a r a c t e r i s t i c s , s u c h as b o d y flexibility o r highly m o b i l e c o n t r o l s u r f a c e s p o s i t i o n e d c l o s e t o t h e c e n t r e o f g r a v i t y ( F i s h , 1 9 9 7 ; Fish et a l . , 2 0 0 3 ) . In c o n t r a s t , a d a p t a t i o n s s u c h a s a rigid b o d y , rigid a p p e n d a g e s , t h e isolation of  2  t h e t h r u s t - p r o d u c i n g unit f r o m t h e rest of t h e b o d y , o r t h e limited mobility o f t h e c o n t r o l s u r f a c e s a r e all r e p r e s e n t a t i v e s of a s t a b l e d e s i g n a n d p o o r m a n o e u v r a b i l i t y . B l a k e eta/.  (1995) show that the  m e a n t u r n i n g radius o f y e l l o w f i n t u n a ( 0 . 4 7 L ) , a rigid t h u n n i f o r m s w i m m e r (a specialist B o d y a n d C a u d a l Fin — B C F — periodic s w i m m e r , W e b b , 1 9 8 4 ) , is m u c h h i g h e r t h a n m o r e flexible t e l e o s t s s u c h as t h e d o l p h i n f i s h ( 0 . 1 3 L ) , t h e s m a l l m o u t h b a s s ( 0 . 1 3 L ) , o r t h e t r o u t ( 0 . 1 8 L). H o w e v e r , m a t t e r s a r e m a d e m o r e c o m p l e x by t h e fact t h a t s o m e r i g i d - b o d i e d s w i m m e r s s u c h a s t h e boxfish h a v e s m a l l t u r n i n g radii ( B l a k e , 1 9 7 7 ; W a l k e r , 2 0 0 0 ) . T h e boxfish u s e s c o m b i n e d oscillations a n d u n d u l a t i o n of t h e p e c t o r a l , d o r s a l a n d a n a l fins ( B l a k e , 1 9 7 7 ) . B l a k e eta/.  (1995) therefore proposed  t h a t o t h e r p a r a m e t e r s , s u c h a s d e c o u p l e d p r o p u l s o r s (i.e. M e d i a n a n d P a i r e d Fins — M P F — f o r s l o w and  tight  manoeuvres, and  BCF motion  for  fast-starts),  play  a  role  in  the  swimming  and  manoeuvring performance of various species.  T h e t u r n s o f m o s t a n i m a l s a r e m a d e up of t w o e l e m e n t s : rotation a n d t r a n s l a t i o n ( e x c e p t i o n s to this rule a r e s o m e M P F s w i m m e r s , w h i c h c a n g e n e r a t e rotation w i t h o u t linear s p e e d , e . g . t h e b o x f i s h ; o r s o m e s p e c i e s t h a t e x h i b i t t r a n s l a t i o n w i t h o u t rotational s p e e d d u e to a differential d e f l e c t i o n of their f i n s , e . g . s e a h o r s e s ) . T h e m o s t s u c c e s s f u l individuals e n g a g e d in p r e d a t o r - p r e y  interactions a r e  typically t h o s e w h o m a x i m i s e b o t h t u r n i n g c o m p o n e n t s , i.e. p e r f o r m a t i g h t t u r n a n d m a i n t a i n a high t r a n s l a t i o n s p e e d ( H o w l a n d , 1 9 7 4 ) . In a r e c e n t s t u d y , M a r e s h et al. ( 2 0 0 4 ) s h o w e d t h a t b o t t l e n o s e d o l p h i n s (also B C F p e r i o d i c s w i m m e r s w i t h a fairly rigid b o d y ) a r e c a p a b l e of h i g h m a n o e u v r a b i l i t y , a s e x h i b i t e d by t h e p i n w h e e l t u r n i n g t e c h n i q u e (also in N o w a c e k , 2 0 0 2 ) . T h i s p i n w h e e l t e c h n i q u e a l l o w s t h e a n i m a l t o m i n i m i s e t u r n i n g r a d i u s a n d m a x i m i s e t u r n i n g r a t e b y t r a n s f o r m i n g its f o r w a r d s p e e d into rotational s p e e d .  T h e relative inflexibility o f s u c h rigid o r g a n i s m s a s t h e boxfish o r t h e b o t t l e n o s e d o l p h i n t h e o r e t i c a l l y i m p a i r s their m a n o e u v r a b i l i t y e v e n t h o u g h t h e y a r e c a p a b l e o f p e r f o r m i n g  t i g h t t u r n s . T h i s is  b e c a u s e t h e a n g l e b e t w e e n t h e b o d y a n d t h e i n c o m i n g f l o w o f a rotating rigid b o d y is c l o s e to 9 0 d e g r e e s a l o n g t h e entire b o d y l e n g t h , w h i c h results in a n i m p o r t a n t p r e s s u r e d r a g a r o u n d t h e b o d y t h a t o p p o s e s rotation a n d c a u s e s d e c e l e r a t i o n . A s e c o n d o u t c o m e of h a v i n g a n inflexible b o d y is t h a t  3  c o u n t e r b a l a n c i n g m o m e n t s of f o r c e a r e c r e a t e d o n b o t h s i d e s o f t h e d o r s o - v e n t r a l rotational a x i s , w h i c h a l s o resists rotation ( W a l k e r , 2 0 0 0 ) . T o m y k n o w l e d g e , no s t u d y has y e t p r o v i d e d d a t a to test t h e s e t w o t h e o r e t i c a l a s s u m p t i o n s in a q u a t i c a n i m a l s .  A n i m a l s m u s t g e n e r a t e a f o r c e in t h e d i r e c t i o n o f t h e m a n o e u v r e t o c h a n g e t h e i r t r a j e c t o r y using a f o r c e p r o d u c e d by t h e b o d y itself, t h e c o n t r o l s u r f a c e s , o r b o t h . In t h e a q u a t i c e n v i r o n m e n t , a c t i v e a n i m a l s c a n g e n e r a t e this f o r c e t h r o u g h e i t h e r a lift-based o r a d r a g - b a s e d m e c h a n i s m , b o t h of w h i c h i n d u c e d r a g . T h i s a d d i t i o n a l d r a g results in m a n o e u v r i n g b e i n g h y d r o d y n a m i c a l l y m o r e costly t h a n s t e a d y s w i m m i n g . T h i s c o n c l u s i o n is s u p p o r t e d b y W e b b ( 1 9 9 1 ) , a n d H u g h e s a n d Kelly ( 1 9 9 6 ) w h o f o u n d t h a t a fish w o r k s h a r d e r w h e n s w i m m i n g at a g i v e n a v e r a g e s p e e d in u n s t e a d y s w i m m i n g t h a n a t t h e s a m e s p e e d in s t e a d y s w i m m i n g .  V a l u a b l e i n f o r m a t i o n o n t h e m i n i m u m a m o u n t o f d r a g e x p e r i e n c e d by s e a lions s w i m m i n g at v a r i o u s s p e e d s c a n b e o b t a i n e d by a n a l y z i n g d e c e l e r a t i o n d u r i n g p a s s i v e g l i d e s . H o w e v e r , d r a g is likely t o b e greater during active s w i m m i n g — and especially during m a n o e u v r e s — d u e to flippers and body m o v e m e n t s ( S t e l l e , 1 9 9 7 ) . A n a l y s i n g t h e details of t h e p e c t o r a l a n d b o d y m o v e m e n t s a n d their effects o n t h e a n i m a l ' s s p e e d c a n t h u s d e e p e n o u r u n d e r s t a n d i n g o f t h e b i o e n e r g e t i c s o f u n s t e a d y s w i m m i n g a n d t h e c o s t s of l o c o m o t i o n .  Some  kinematic  data  have  b e e n c o l l e c t e d for  otariids  on  swimming  speeds,  pectoral  flipper  p r o p u l s i o n , t u r n i n g r a d i u s , t u r n i n g rate, a n d g e n e r a l t u r n i n g t e c h n i q u e ( E n g l i s h , 1 9 7 6 ; F e l d k a m p , 1 9 8 7 a ; Fish e t a l . , 2 0 0 3 ; P o n g a n i s e t a l . , 1 9 9 0 ) . T h e y s u g g e s t t h a t o t a r i i d s h a v e s e v e r a l k i n e m a t i c f e a t u r e s t h a t e n h a n c e t h r u s t p r o d u c t i o n a s w e l l a s m a n o e u v r a b i l i t y . First, t h e i r t h r u s t p r o d u c t i o n t e c h n i q u e is b a s e d o n b o t h a lift- a n d a d r a g - b a s e d m e c h a n i s m , w h i c h a l l o w s t h e m t o p r o d u c e a m a x i m u m a m o u n t o f t h r u s t t h r o u g h o u t t h e s t r o k e c y c l e . S e c o n d , t h e i r b o d y d e s i g n is ideal for p r o m o t i n g instabilities (i.e., t h e y h a v e a highly flexible b o d y t h a t h a s a r o u n d c r o s s - s e c t i o n a n d large m o b i l e p e c t o r a l flippers p l a c e d c l o s e to t h e c e n t r e of g r a v i t y ) .  California s e a lions a r e a m o n g t h e m o s t m a n o e u v r a b l e of m a r i n e m a m m a l s w h e n c o m p a r e d t o s p e c i e s t h a t s w i m a t m e c h a n i c a l l y e q u i v a l e n t s p e e d s (Fish et a l . , 2 0 0 3 ) . H o w e v e r , k n o w l e d g e a b o u t  4  t h e k i n e m a t i c s o f o t h e r otariids is limited. T h e Steller s e a lion is a n ideal s t u d y a n i m a l to e x p a n d c u r r e n t k n o w l e d g e a b o u t t h e m a n o e u v r a b i l i t y o f otariids. B e i n g t h e l a r g e s t o f t h e f a m i l y , Steller s e a lions e x p e r i e n c e a high v a l u e of d r a g a n d i m p o r t a n t inertial f o r c e s , b o t h o f w h i c h a r e likely to constrain manoeuvrability.  D r a g is a b a c k w a r d s a c t i n g f o r c e t h a t o p p o s e s f o r w a r d  motion,  and  inertial f o r c e s t e n d to m a i n t a i n t h e directionality a n d resist a c h a n g e in t r a j e c t o r y w h i l e s w i m m i n g . S t u d y i n g d e t a i l e d k i n e m a t i c s a n d m o r p h o l o g i c a l a d a p t a t i o n s will p r o v i d e i n f o r m a t i o n o n h o w Steller s e a lions m a n a g e t h e s e c o n s t r a i n t s t o o p t i m i z e t u r n i n g c a p a b i l i t i e s a n d s w i m m i n g v e l o c i t i e s .  T o provide data about the detailed biomechanics of an unstable body design during a manoeuvre, I r e p e a t e d l y f i l m e d 3 Steller s e a lions p e r f o r m i n g 180 d e g r e e t u r n s . w e r e t r a c k e d digitally  t h r o u g h o u t t h e m a n o e u v r e s using t h r e e  M o v e m e n t s o f t h e flexible b o d y markers placed along the  body  m i d l i n e . T h e s e q u e n c e o f resulting m o v e m e n t s w a s c o r r e l a t e d w i t h d e t a i l e d s p e e d v a r i a t i o n s a n d w i t h t h e f o r c e s a c t i n g o n t h e c e n t r e of gravity t h r o u g h o u t t h e m a n o e u v r e s . T h e e v a l u a t i o n  of  a c c e l e r a t i o n (positive a n d n e g a t i v e ) d u r i n g t h e t u r n a l s o p r o v i d e d practical i n f o r m a t i o n r e g a r d i n g t h e p o w e r r e q u i r e m e n t s a n d e n e r g e t i c s o f a m a n o e u v r i n g s e a lion.  MATERIALS AND METHODS All p r o c e d u r e s a n d p r o t o c o l s involving a n i m a l s w e r e c o n d u c t e d u n d e r t h e a u t h o r i t y o f t h e University o f British C o l u m b i a A n i m a l C a r e P e r m i t N o . A 0 4 - 0 1 6 9 .  Morphology Morphological  measurements were  taken  on three  female  Steller s e a lions a t t h e  Vancouver  A q u a r i u m M a r i n e S c i e n c e C e n t r e ( V a n c o u v e r , B C , C a n a d a ) . T w o f e m a l e s w e r e 3 y e a r old j u v e n i l e s ( F 0 0 Y A a n d FOOTS — later referred to as S L 1 a n d S L 2 r e s p e c t i v e l y ) a n d t h e t h i r d f e m a l e w a s a 6 y e a r old a d u l t ( F 9 7 H A — r e f e r r e d to a s S L 3 ) . M e a s u r e m e n t s w e r e g a t h e r e d o n e a c h a n i m a l prior t o t h e f i l m e d e x p e r i m e n t s . T o t a l length w a s m e a s u r e d f r o m t h e tip of t h e n o s e to t h e tip o f t h e h i n d flippers. S t a n d a r d length w a s t a k e n f r o m t h e tip o f t h e n o s e to t h e b a s e o f t h e t a i l .  Fig. 1:  3 - D r e p r e s e n t a t i o n of t h e b o d y of S L 3 a s o b t a i n e d f r o m girth m e a s u r e m e n t s . G 1 - G 8  r e p r e s e n t girth m e a s u r e m e n t s 1 to 8 a n d f o r m t h e b a s e a n d t h e t o p o f e a c h t r u n c a t e d c o n e . D i s t a n c e s b e t w e e n e a c h girth m e a s u r e m e n t ( d l - d 8 ) p r o v i d e t h e  height o f t h e  truncated  c o n e s . C G i n d i c a t e s t h e c e n t r e of g r a v i t y , j u s t b e f o r e t h e trailing e d g e o f t h e p e c t o r a l f l i p p e r s .  Body volume and wetted surface area were calculated as a succession of truncated cones. Eight girth m e a s u r e m e n t s w e r e t a k e n a t k n o w n intervals a l o n g t h e b o d y (the e a r s , t h e neck, directly in f r o n t o f t h e p e c t o r a l f l i p p e r s , directly b e h i n d t h e pectoral f l i p p e r s , t w o p l a c e s a l o n g t h e t r u n k region b e t w e e n flippers a n d hips, t h e hips, a n d t h e position w h e r e t h e b o d y a n d t h e hind flippers m e e t ) , e a c h f o r m i n g t h e b a s e of a t r u n c a t e d c o n e ( F i g . 1). T h e a n i m a l s w e r e w e i g h e d daily o n a G S E s c a l e , M o d e l 3 5 0 (scale a c c u r a c y ± 0 . 1 k g ) . B o d y d e n s i t y w a s o b t a i n e d by d i v i d i n g t h e c a l c u l a t e d v o l u m e (including t h e v o l u m e of t h e f l i p p e r s , s e e b e l o w ) by t h e m a s s of t h e a n i m a l .  6  T h e location of t h e c e n t r e of g r a v i t y w a s d e t e r m i n e d u s i n g t h e m e t h o d o f D o m n i n g a n d D e Buffrenil ( 1 9 9 1 ) . In brief, a n a n a e s t h e t i s e d s e a lion w a s p l a c e d o n a flat b o a r d w i t h t h e p e c t o r a l flippers lying flat a g a i n s t its flank. T h e b o a r d a n d s e a lion w e r e t h e n c a r e f u l l y b a l a n c e d in a s e e s a w f a s h i o n o n a steel pipe. T h e position of the equilibrium point corresponded to the centre of m a s s of both the a n i m a l a n d t h e flat b o a r d t o g e t h e r . T h e e x a c t position o f t h e a n i m a l ' s C G f r o m t h e tip o f t h e n o s e w a s t h e n c a l c u l a t e d by s u b t r a c t i n g t h e effect of t h e b o a r d . T h e relative p o s i t i o n of t h e C G w a s t h u s :  _ , ..  ...  R e l a t i v e C G position =  distance nose -CG standard length  ...  100 .  T h e d i s t a n c e b e t w e e n t h e n o s e a n d t h e position o f m a x i m u m t h i c k n e s s w a s a l s o m e a s u r e d w h i l e t h e a n i m a l w a s a n a e s t h e t i s e d a n d t h e relative position o f t h e m a x i m u m t h i c k n e s s w a s c a l c u l a t e d u s i n g :  „ . ...  .... .  ....  R e l a t i v e m a x t h i c k n e s s position =  distance nose - max thickness standard length  .  Anr  100 .  A s t w o of t h e t h r e e s t u d y a n i m a l s w e r e still g r o w i n g j u v e n i l e s , b o d y m a s s w a s m e a s u r e d daily. A d d i t i o n a l m e a s u r e m e n t s o f b o d y length a n d 4 girths w e r e t a k e n a t least o n c e a w e e k . F l u c t u a t i o n s in m a s s w e r e o b s e r v e d d u r i n g t h e c o u r s e of t h e s t u d y ( b e t w e e n 5 . 6 % a n d 7 . 6 % o f t h e  body  w e i g h t ) . I d e t e r m i n e d t h e p o s s i b l e m o r p h o l o g i c a l implications o f this w e i g h t c h a n g e by looking at t h e lifetime m o r p h o l o g i c a l d a t a o f e a c h a n i m a l ( F i g . 2 ) . B a s e d o n t h e l o n g - t e r m  relationships  b e t w e e n w e i g h t a n d girths ( G 3 , G 4 , G 7 a n d G 8 , s e e F i g . 2) I d e t e r m i n e d t h a t a girth m e a s u r e m e n t e r r o r of 3 % c o v e r e d t h e p o s s i b l e m o r p h o l o g i c a l effects o f t h e c h a n g e in m a s s t h a t o c c u r r e d o v e r t h e course of the study.  SL1 160 ,120  y - 0.42x + 77.69  R a 0.87  y = 0.34x + 7S.17  R = 0.87  y • 0.27X + 44.99  R =0.50  y a 0.12x + 39.70  H a 0.33  2  2  2  ' 80 1  40 0 SO  90  100  110  120  130  150  HC  160  170  SL2 160  y = 0.38x + 84.63  R - 0.80  y - 0.33x + 80.47  R = 0.79 J  !  ^ ^ r - ^  y = G.34x + 36.37 ; R*=0.62  ' 80  y = 0.12x + 41.58 ; R = 0.40 S  40 0 E-3  90  100  110  120  140  120  152  160  172  SL3 160  y a 0.40x + 80.60  :0.89  y a 0.35X + 77.32  :0.91  y - 0.24x + 52.88 ; RfaO.53 y = O.llx + 44.75 ; R =0.49 2  f t 1  80  90  UO  100  130  1 1 1  140  •M:  Mass [kg] I GO  G4  ©67  OG8  Fig. 2: Lifetime variation of 4 girth measurements as a function of body mass. Each cloud of data represents the girth of one cross-section of the body (see Fig. 1): G3 is taken just in front of the pectoral flippers; G4, just posterior to the pectoral flippers; G7 on the hipbone; and G8 on the base of the tail. The dashed lines indicate the minimum and maximum weight of each animal over the study period.  8 Flipper m e a s u r e m e n t s w e r e o b t a i n e d via 2 d i f f e r e n t t e c h n i q u e s . T h e p r o j e c t e d s u r f a c e a r e a , length of t h e flipper f r o m t h e insertion to t h e tip o f t h e a p p e n d a g e a n d w i d t h o f t h e flipper w e r e t a k e n f r o m s c a l e d still p h o t o g r a p h s a n a l y s e d o n a P C w i t h S c i o n I m a g e s o f t w a r e ( B e t a v e r s i o n 4 . 0 . 2 ) . T h i c k n e s s m e a s u r e m e n t s w e r e o b t a i n e d w i t h a spring-joint accuracy:  ±0.5mm)  at  13  locations  along  the  calliper a n d a millimetric pectoral  flipper  while  the  ruler  (measurement  animal  was  under  a n a e s t h e t i c s . T h e 13 m e a s u r e m e n t s w e r e l o c a t e d a s f o l l o w : 4 a l o n g t h e l e a d i n g e d g e , 4 a l o n g t h e m i d l i n e , 4 a l o n g t h e trailing e d g e , a n d 1 at t h e tip (all m e a s u r e m e n t s w e r e a p p r o x i m a t e l y  15cm  a p a r t ) . T h e flipper A s p e c t R a t i o ( A R ) w a s c a l c u l a t e d a s :  AR=  {lengthf {projected surface area)'  T h e v o l u m e o f t h e pectoral flipper w a s c a l c u l a t e d by a s s u m i n g t h a t it w a s e q u i v a l e n t t o a s u c c e s s i o n o f t r u n c a t e d , s q u a r e - b a s e d p y r a m i d s ( t h e t h i c k n e s s o f t h e b a s e o f t h e p y r a m i d is t h e a v e r a g e t h i c k n e s s o f t h e l e a d i n g a n d trailing e d g e s of t h e flipper). T h e s e m e a s u r e m e n t s w e r e t a k e n o n o n e a p p e n d a g e o n l y , a n d it w a s a s s u m e d t h a t b o t h f l i p p e r s w e r e i d e n t i c a l . T h e v o l u m e o f t h e p e l v i c flippers w a s c a l c u l a t e d a s a p e r c e n t a g e o f t h e v o l u m e of t h e p e c t o r a l f l i p p e r s . T h i s p e r c e n t a g e w a s g i v e n b y t h e ratio o f t h e s u r f a c e a r e a s o f t h e pelvic a n d p e c t o r a l f l i p p e r s . T h e s e v a l u e s w e r e u s e d in the calculation of the total volume of the animal.  Fig. 3: On-screen morphological measurements of the left pectoral flipper of S L 3 . The white dots indicate points where thickness of the flipper was measured with a springjoint calliper.  Fig. 4: On-screen morphological measurements of the left pelvic flipper of S L 3 . Length was measured from the base of the tail to the tip of the middle digit. Width was measured perpendicular to the flipper longitudinal axis at the base of the digital extensions.  10  Experimental  set-up  T h e a n i m a l s w e r e kept in a n o u t d o o r facility w i t h c o n s t a n t a c c e s s to a m b i e n t , filtered s e a w a t e r ( R o s e n a n d T r i t e s , 2 0 0 4 ) . T e s t s w e r e p e r f o r m e d in a 1 9 m l o n g , 5 m d e e p pool w i t h rock a n d w o o d e n h a u l - o u t a r e a s . D u r i n g t h e c o u r s e o f t h e s t u d y , t h e a n i m a l s w e r e f e d p r e d o m i n a n t l y Pacific h e r r i n g . I n a d d i t i o n t o t h e d a i l y w e i g h t m e a s u r e m e n t s , m o r p h o l o g i c a l d a t a (i.e. l e n g t h a n d girths)  was  gathered once a week.  Data w e r e collected from August 1 5  t h  t o D e c e m b e r 3 , 2 0 0 3 . E x p e r i m e n t s o c c u r r e d o v e r a period of r d  11 d a y s w i t h S L 3 , 5 0 d a y s w i t h S L 1 , a n d 2 9 d a y s w i t h S L 2 .  T h e training t e c h n i q u e u s e d w a s similar t o t h a t u s e d by Fish ( 2 0 0 3 ) . U s i n g p o s i t i v e  reinforcement,  t h e s e a lions w e r e t r a i n e d t o s w i m b a c k a n d f o r t h b e t w e e n t w o t r a i n e r s p o s i t i o n e d a t o p p o s i t e e n d s of t h e t e s t p o o l . A s t h e a n i m a l a p p r o a c h e d T r a i n e r 2 , T r a i n e r 1 w o u l d p e r f o r m a recall signal (i.e. hit t h e s u r f a c e o f t h e w a t e r w i t h a t a r g e t pole) indicating to t h e a n i m a l t o i m m e d i a t e l y r e t u r n t o T r a i n e r 1. T h e a n i m a l w o u l d t h e n e x e c u t e a 1 8 0 - d e g r e e s t u r n t o c h a n g e its d i r e c t i o n . P r e l i m i n a r y t e s t i n g revealed that the longer the distance between the trainers, the lower the animal's swimming speed. H a v i n g o n e t r a i n e r sitting in a k a y a k p o s i t i o n e d 3-5 m e t r e s f r o m t h e field o f v i e w o f t h e v i d e o c a m e r a c o n s e q u e n t l y r e d u c e d this d i s t a n c e . E v e n t h o u g h t h e d i s t a n c e b e t w e e n t h e t w o  trainers  v a r i e d ( b e t w e e n 9 a n d 12 m e t r e s ) , I e n s u r e d t h a t t h e a n i m a l h a d r o o m for at least o n e c o m p l e t e flipper s t r o k e b e f o r e e n t e r i n g t h e field o f v i e w o f t h e c a m e r a .  T h e 1 8 0 - d e g r e e s t u r n s w e r e f i l m e d w i t h a digital v i d e o c a m e r a ( C a n o n G L - 2 ) a t t a c h e d 5 m a b o v e t h e water  surface. T h e filming  rate w a s set at 6 0 f r a m e s  p e r s e c o n d a n d t h e z o o m setting  was  e q u i v a l e n t to a 3 9 . 5 m m o p e n i n g o n a 3 5 m m f o c a l l e n g t h , w h i c h c o r r e s p o n d e d to a d i a g o n a l a n g l e of 5 7 . 4 2 ° ( a n g l e f o r m e d a t t h e a p e x of t h e triangle d e f i n e d by t w o o p p o s i t e c o r n e r s of t h e field o f v i e w a n d t h e focal point o f t h e c a m e r a ) . T o r e d u c e flares a n d s u r f a c e reflections, t h e c a m e r a w a s m o u n t e d w i t h a circular polarising filter ( H o y a circular polarising filter, 5 8 m m , p i t c h : 0 . 7 5 ) . A c l e a r Plexiglas s h e e t ( d i m e n s i o n s : 2.61 m e t r e s by 1.98 m e t r e s ) f l o a t e d o n t h e w a t e r s u r f a c e in t h e c e n t r e  11  of the field of view of the camera to eliminate visual distortions produced by the surface waves. Only the turns that occurred directly under the Plexiglas sheet were analysed.  Fig. 5:  Schematic of the experimental set-up.  A number of temporary marks were drawn on the fur of the test animals that could be tracked on the video images. Oil-based pastel crayons were used because the captive animals could not be marked with long-lasting paint. The dots were visible for 48 hours before having to be reapplied. However, an oil-based zinc cream was used (Desitin, Zinc Oxide 37%, Cod Liver Oil 13.5%) for one of the three test animals. This was quicker to apply but it had to be re-applied during the experiments because it faded faster while the animal was in the water. The first point was placed on the shoulder blades to represent the movements of the anterior part of the body during each manoeuvre. The second point was situated at the centre of gravity of the animal lying flat with its pectoral flipper tucked in. The third point was placed on the hipbone to represent the movements of the posterior part of the body during turns. Each visual marking was drawn 3 times around the  12  a n i m a l g i r t h s : o n t h e left s i d e , o n t h e right s i d e , a n d a l o n g t h e b a c k b o n e . T h u s a t o t a l o f 9 d o t s ( r o u g h l y 2 . 5 c m in d i a m e t e r ) w e r e p a i n t e d o n e a c h t e s t a n i m a l .  Video  analysis  D u r i n g e a c h m a n o e u v r e , a s e r i e s o f 12 e v e n t s w e r e identified a n d c l a s s i f i e d in a t i m e s e q u e n c e t o illustrate t h e t u r n i n g t e c h n i q u e o f e a c h a n i m a l . T h e s e 12 c o m p o n e n t s w e r e : 1) m o v e m e n t of t h e h e a d inside t h e t u r n ; 2) start o f t h e a b d u c t i o n o f t h e pectoral f l i p p e r s ; 3 ) s t a r t o f t h e roll o f t h e b o d y ; 4) o p e n i n g o f t h e interdigital w e b of t h e pelvic f l i p p e r s ; 5) start of t h e d o r s a l f l e x i o n ; 6) e n d o f t h e a b d u c t i o n o f t h e p e c t o r a l f l i p p e r s ; 7) m a x i m u m r o l l ; 8) m i n i m u m radius o f c u r v a t u r e of t h e f l e x e d b o d y ; 9) start of t h e a d d u c t i o n o f t h e pectoral f l i p p e r s ; 10) b o d y b a c k in a straight p o s i t i o n ; 11) e n d o f t h e a d d u c t i o n o f t h e pectoral f l i p p e r ; 12) t h e pelvic flippers r e t u r n to a p a s s i v e , gliding p o s i t i o n .  T h e d e p t h at t h e b e g i n n i n g a n d e n d of a m a n o e u v r e o c c a s i o n a l l y d i f f e r e d b e c a u s e t h e m o t i o n of t h e a n i m a l s w a s not limited vertically. W h e n this h a p p e n e d , t h e t u r n i n g r a d i u s a s s e e n in 2 d i m e n s i o n s by t h e c a m e r a p l a c e d o v e r h e a d (with its a x i s n o r m a l to t h e w a t e r s u r f a c e ) a p p e a r s s m a l l e r t h a n it really is in 3 d i m e n s i o n s . T h i s w a s c o r r e c t e d u s i n g a s c a l e t h a t linked t h e size o f a n o b j e c t o n s c r e e n to its d e p t h : i.e. a visual s c a l e (a 2 m long ruler w i t h 1 0 c m b l a c k a n d w h i t e i n c r e m e n t s ) w a s built a n d f i l m e d in t h e e x p e r i m e n t a l s e t - u p at v a r i o u s k n o w n d e p t h s . F r o m t h i s , a m a t h e m a t i c a l relationship w a s o b t a i n e d t h a t linked t h e t w o entities:  Depth = -0.0564  (Size o n s c r e e n in pixels) + 8 . 6 3 3 .  T h e object m e a s u r e d before a n d after e a c h m a n o e u v r e w a s t h e distance b e t w e e n the hip a n d the s h o u l d e r d o t s , w h i c h w a s m e a s u r e d digitally o n s c a l e d v i d e o i m a g e s t h e d a y o f t h e trial.  13  T u r n i n g radii, i n s t a n t a n e o u s s p e e d a t t h e start a n d e n d of a t u r n , a v e r a g e s p e e d , a c c e l e r a t i o n , d e c e l e r a t i o n , rolling d e g r e e , a n d d u r a t i o n of t h e m a n o e u v r e w e r e all m e a s u r e d f r o m t h e s c a l e d v i d e o clips using L e n o x S o f t w o r k s ' V i d e o p o i n t 2 . 5 . All m a n o e u v r e s w e r e r e f e r e n c e d to a n o n - s c r e e n origin t h a t w a s p o s i t i o n e d 16 pixels right a n d 16 pixels u p f r o m t h e b o t t o m left c o r n e r o f t h e i m a g e .  T h e positions of t h e t h r e e lateral d o t s ( s h o u l d e r , C G , a n d hips) w e r e m a n u a l l y t r a c k e d at a s a m p l i n g rate of 3 0 H z . O n m o s t i m a g e s , t h e painted m a r k s c o v e r e d a s u r f a c e of a f e w pixels o n s c r e e n (typically b e t w e e n 2 a n d 9 s q u a r e pixels). T h e e x a c t position of e a c h m a r k h a d t o b e d e t e r m i n e d s u b s e q u e n t l y u s i n g t h e s p e e d profiles ( s e e b e l o w ) .  Instantaneous speed w a s calculated as:  .. _ P n+1 ~ Pn-1 tn+1  tn-1  w h e r e U is t h e i n s t a n t a n e o u s s p e e d o f p o i n t n (in m / s ) , P n  n + 1  a n d P _ i a r e t h e p o s i t i o n s o f t h e points n  directly after a n d b e f o r e point n respectively (in m ) , a n d t +i a n d t - i is t h e t i m e c o d e of t h e points n  n  directly after a n d b e f o r e point n respectively (in s ) . T h e s p e e d profile w a s o b t a i n e d by  plotting  i n s t a n t a n e o u s velocities o v e r t i m e . T h e s p e e d c u r v e w a s t h e n s m o o t h e n e d b y m o v i n g t h e t r a c k points a f e w pixels left, right, up, o r d o w n w i t h i n t h e o n s c r e e n s u r f a c e of t h e p a i n t e d dot. T h i s d e t e r m i n e d t h e e x a c t position of t h e m a r k e r o n s c r e e n . T o c o r r e c t for t h e d i f f e r e n c e of d e p t h before a n d after t h e m a n o e u v r e , t h e s p e e d calculation w a s m o d i f i e d , s u c h a s :  Uncorrected) -  c  Q  S  a  ,  w h e r e a is t h e a n g l e t h a t d e s c r i b e s t h e d i f f e r e n c e of d e p t h .  T u r n i n g radius ( R ) w a s c a l c u l a t e d m a t h e m a t i c a l l y by fitting a half-circle t o t h e c u r v e d part of t h e trajectories o f t h e s h o u l d e r , t h e c e n t r e o f g r a v i t y , a n d t h e hip u s i n g l e a s t s q u a r e d r e g r e s s i o n s (i.e. t h r e e t u r n i n g radii w e r e o b t a i n e d per m a n o e u v r e ) . T h e trajectories o b t a i n e d in V i d e o p o i n t 2.5 w e r e imported  into S - P L U S 6 . 1 , w h e r e t h e least s q u a r e d r e g r e s s i o n s w e r e p e r f o r m e d . O n c e R w a s  m e a s u r e d , t h e real t u r n i n g radius w a s o b t a i n e d by t a k i n g t h e d e p t h d i f f e r e n c e into a c c o u n t :  14  Rreal ~ ^( Rmeasured )  +  \^~2~ J '  w h e r e R is t u r n i n g r a d i u s , a n d A D is t h e d i f f e r e n c e of d e p t h b e t w e e n t h e e n t r a n c e a n d exit o f a manoeuvre.  N e g a t i v e a n d p o s i t i v e a c c e l e r a t i o n s w e r e o b t a i n e d b y c a l c u l a t i n g t h e s l o p e o f t h e b e s t fitting line t h r o u g h t h e a p p r o p r i a t e portion o f t h e t i m e - s p e e d g r a p h (i.e. o n e line w a s fitted to t h e d e c e l e r a t i n g s e c t i o n o f t h e g r a p h a n d a n o t h e r w a s fitted to t h e a c c e l e r a t i n g s e c t i o n ) . T h e s e portions o f t h e d a t a set w e r e identified v i s u a l l y .  T h e s p e e d at t h e b e g i n n i n g of t h e t u r n w a s d e f i n e d a s t h e i n s t a n t a n e o u s s p e e d of t h e a n i m a l j u s t b e f o r e t h e first m a n o e u v r i n g m o v e m e n t ( m o s t o f t h e t i m e , a h e a d m o v e m e n t a n d t h e a b d u c t i o n o f t h e pectoral f l i p p e r s ) . T h e s p e e d at t h e e n d o f a m a n o e u v r e w a s d e f i n e d a s t h e i n s t a n t a n e o u s s p e e d of t h e a n i m a l a s s o o n as t h e midline o f t h e b o d y h a d r e g a i n e d a s t r a i g h t p o s i t i o n , w i t h t h e p e c t o r a l flippers a d d u c t e d a l o n g t h e b o d y f l a n k s . Rolling d e g r e e c o u l d not b e m e a s u r e d directly in d e g r e e s o r r a d i a n s using t h e o n e c a m e r a a n g l e . I n s t e a d , a n index o f roll w a s u s e d to g i v e a s e n s e of h o w m u c h a n d h o w f a s t t h e a n i m a l t u r n e d its b a c k into t h e t u r n b e f o r e e x e c u t i n g t h e m a n o e u v r e . T h i s 'rolling index' — tracked at 30Hz throughout the turn — w a s defined as the distance, normal to the body a x i s , b e t w e e n t h e s h o u l d e r m a r k e r a n d t h e e d g e of t h e b o d y as s e e n o n t h e t o p - d o w n c a m e r a v i e w . T h i s d i s t a n c e t h e r e f o r e d e c r e a s e d w i t h a n i n c r e a s i n g rolling d e g r e e ( u p t o a m a x i m u m rolling d e g r e e o f 180 d e g r e e s — w h i c h c o r r e s p o n d e d to a d i s t a n c e of Ocm).  T h e rolling i n d e x a l s o p r o v i d e d i n f o r m a t i o n o n h o w f a s t a s e a lion r o l l e d . It w a s m e a s u r e d b e t w e e n t h e " t i m e o f e n t e r i n g " (i.e. t h e t i m e at w h i c h t h e i n s t a n t a n e o u s e n t e r i n g s p e e d w a s m e a s u r e d ) a n d t h e t i m e of m a x i m u m roll (i.e. w h e n t h e rolling index is m i n i m a l o r , in o t h e r w o r d s , w h e n  the  d i s t a n c e b e t w e e n t h e s h o u l d e r m a r k e r a n d t h e e d g e of t h e b o d y — a s s e e n f r o m a b o v e — w a s m i n i m a l ) . T h e d u r a t i o n of a m a n o e u v r e w a s d e f i n e d a s t h e t i m e e l a p s e d b e t w e e n t h e " t i m e o f entering" and the "time of exiting".  F r o m t h e i n s t a n t a n e o u s s p e e d d a t a of t h e t h r e e m a r k e r s , I o b t a i n e d t h e r e s u l t a n t a c c e l e r a t i o n :  15  _ Up+i ~ Up-i  dp —  where a  tp+1 ~ tp-l  i  is t h e i n s t a n t a n e o u s resultant a c c e l e r a t i o n of point p (in m / s ) , U 2  p  p +  i and U -i are the p  i n s t a n t a n e o u s velocities o f t h e points directly a f t e r a n d b e f o r e p o i n t p r e s p e c t i v e l y (in m / s ) , a n d  t  p + 1  a n d tp-i is t h e t i m e c o d e of t h e points directly after a n d before point p r e s p e c t i v e l y (in s ) . T h e m e a s u r e m e n t o f a c c e l e r a t i o n ( a n d t h e r e f o r e f o r c e ) w a s v e r y s e n s i t i v e t o t h e position o f t h e m a r k e r s o n e a c h f r a m e . I t h e r e f o r e fitted t h e p o s i t i o n - t i m e d a t a w i t h a p o l y n o m i a l f u n c t i o n of t h e 6  t h  d e g r e e , a n d c a l c u l a t e d t h e s e c o n d derivative of this p o l y n o m i a l f u n c t i o n t o o b t a i n a c c e l e r a t i o n . T h i s p r o c e s s p r o v i d e d t h e X a n d Y c o m p o n e n t s of t h e a c c e l e r a t i o n v e c t o r , w h i c h w e r e t h e n t r a n s l a t e d a n d rotated to t r a c k t h e f o r w a r d velocity v e c t o r (i.e. t h e velocity v e c t o r h a v i n g n o X c o m p o n e n t in t h e n e w referential s y s t e m ) . C a l c u l a t i n g t h e X a n d Y c o m p o n e n t s of t h e a c c e l e r a t i o n v e c t o r in this new  referential  (tangential  system provided one component  acceleration a ) t  and one component  parallel to t h e p e r p e n d i c u l a r to  i n s t a n t a n e o u s velocity the  velocity vector  vector (normal  a c c e l e r a t i o n a ) . T a n g e n t i a l force w a s F = m a a n d n o r m a l f o r c e w a s d e f i n e d a s F = m a . n  T h e d e g r e e of c u r v a t u r e  t  of the flexing  t  body was quantified  n  by c a l c u l a t i n g t h e  n  radius of  the  c i r c u m c i r c l e t h a t p a s s e d t h r o u g h e a c h o n e of the t h r e e o n - s c r e e n m a r k e r s . H o w e v e r , t h e d e g r e e of c u r v a t u r e of t h e b o d y w a s clearly i n f l u e n c e d b y t h e position o f t h e h e a d d u r i n g t h e t u r n , w h i c h w a s not c a p t u r e d by t h e m a r k e r s located o n t h e s h o u l d e r , C G a n d hips of t h e a n i m a l . T h e r e f o r e , t h e position of t h e a n i m a l ' s n o s e w a s t r a c k e d u s i n g a f o u r t h m a r k e r o n 3 1 t u r n s ( S L 1 : 6 ; S L 2 : 9 ; S L 3 : 16) to p r o v i d e i n f o r m a t i o n o n t h e h e a d ' s position a n d its i m p o r t a n c e in t h e k i n e m a t i c s of t h e t u r n .  A N O V A tests w e r e p e r f o r m e d o n v a r i o u s p a r a m e t e r s d e s c r i b e d a b o v e (i.e. e n t e r i n g s p e e d , e x i t i n g s p e e d , rolling t i m e , t u r n d u r a t i o n , d e c e l e r a t i o n , a c c e l e r a t i o n , a n d t u r n i n g radius) to d e t e r m i n e intera n i m a l d i f f e r e n c e s a n d d i f f e r e n c e s b e t w e e n v a r i o u s b o d y parts ( S P S S 8 . 0 ) . R e s u l t s w e r e c o n s i d e r e d significant a t P < 0 . 0 5 .  16  RESULTS Morphology T h e m o r p h o l o g i c a l d a t a for e a c h o f t h e t h r e e s e a lions is p r e s e n t e d in T a b l e s 1, 2 , a n d 3, a s w e l l as Figs 1, 3 , a n d 4 . T h e d a t a s h o w n in T a b l e s 2 a n d 3 w e r e o b t a i n e d prior t o t h e first trial o f e a c h animal. T h e animals' weights fluctuated over the course of the study. T h e m a x i m u m mass change for e a c h a n i m a l o v e r t h e s t u d y period w a s 7 . 6 % for S L 1 , 5 . 8 % for S L 2 , a n d 5 . 6 % for S L 3 . B o d y length s h o w e d c o n s i d e r a b l y less variation w i t h a n a v e r a g e i n c r e a s e o f 0 . 6 5 % ( r a n g e 0 . 2 2 - 1 . 4 3 % ) . T h e h i g h e s t v a l u e s o f t h e r a n g e w e r e u s e d to d e t e r m i n e t h e u n c e r t a i n t i e s o f t h e  morphological  m e a s u r e m e n t s directly a f f e c t e d by m a s s v a r i a t i o n s ( T a b l e 2 ) .  W i t h t h e e x c e p t i o n o f t h e h i p b o n e a r e a ( w h e r e t h e b o d y is slightly d o r s o - v e n t r a l l y c o m p r e s s e d ) , t h e b o d y o f t h e Steller s e a lions has a r o u n d e d c r o s s s e c t i o n w h e n in t h e w a t e r ( p e r s o n a l o b s e r v a t i o n s ) . T h e r e f o r e , a c i r c u l a r c r o s s - s e c t i o n w a s a s s u m e d in all c a l c u l a t i o n s o f v o l u m e , w e t t e d s u r f a c e a r e a , and frontal surface a r e a .  Pectoral flippers a n d pelvic f l i p p e r s r e p r e s e n t e d 5 5 . 7 5 % a n d 4 4 . 2 5 % o f t h e t o t a l p r o j e c t e d flipper a r e a respectively. T h e m e a n a s p e c t ratio of t h e p e c t o r a l flippers w a s 3 . 2 3 , a n d t h e m e a n a s p e c t ratio of t h e pelvic flippers w a s 2 . 3 9 .  Table 1:  M a s s of t h e t h r e e f e m a l e Steller s e a lions: S L 1 , S L 2 , a n d S L 3 o n t h e d a y of t h e f i l m e d trials.  Animal  Age [yrs]  Birth year  Date [dd-mm-yyyy]  Mass [kg]  SL1  3  2000  12-08-2003  124.6  15-08-2003  126.5  18-08-2003 22-08-2003  127.0 ' 128.4  13-09-2003  118.7  15-09-2003  121.2  SL2  SL3  3  6  2000  1997  19-09-2003  121.5  03-10-2003  125.5  30-10-2003  138.8  05-11-2003  142.9  06-11-2003 07-11-2003  142.8  11-11-2003  144.7  12-11-2003 25-11-2003  145.9 146.4  27-11-2003  147.3  03-12-2003  147.3  03-07-2003  138.2  28-08-2003  145.2  143.6  29-08-2003  145.8  30-08-2003  145.6  31-08-2003  145.4  02-09-2003  145.7  07-09-2003  146.4  18  Table 2:  M o r p h o l o g i c a l d a t a c o l l e c t e d o n t h r e e f e m a l e Steller s e a lions. T h e s e m e a s u r e m e n t s w e r e o b t a i n e d o n c e f o r e a c h a n i m a l b e f o r e t h e i r first f i l m e d t r i a l . T o t a l l e n g t h r e p r e s e n t s t h e length o f t h e a n i m a l f r o m t h e n o s e t o t h e tip o f t h e pelvic flippers. S t a n d a r d l e n g t h r e p r e s e n t s length to t h e b a s e of t h e t a i l , a n d frontal s u r f a c e a r e a c o r r e s p o n d s to t h e s u r f a c e o f t h e largest c r o s s - s e c t i o n of t h e a n i m a l . F i n e n e s s ratio w a s c a l c u l a t e d a s : ( m a x l e n g t h ) / ( m a x b r e a d t h ) . T h e p o s i t i o n o f t h e c e n t r e of gravity of t h e a n i m a l lying s t r e t c h e d w a s d e t e r m i n e d u s i n g t h e t e c h n i q u e d e s c r i b e d by D o m n i n g a n d D e Buffrenil ( 1 9 9 1 ) . T o t a l l e n g t h , s t a n d a r d l e n g t h , f r o n t a l s u r f a c e a r e a , p o s i t i o n o f m a x i m u m t h i c k n e s s , a s w e l l a s C G position w e r e o b t a i n e d w h i l e t h e a n i m a l w a s u n d e r a n a e s t h e s i a . T h e v o l u m e is o b t a i n e d f r o m a s e r i e s o f t r u n c a t e d c o n e s ( s e e F i g . 1) d e f i n e d by 8 girth m e a s u r e m e n t s t a k e n a t k n o w n intervals a l o n g t h e b o d y o f t h e a n i m a l . A l l m e a s u r e m e n t s a n d c a l c u l a t i o n s o f t h e p e c t o r a l a n d pelvic flippers w e r e o b t a i n e d f r o m d i g i t a l , s c a l e d pictures ( s e a Figs 3 a n d 4 ) . P e c t o r a l length r e p r e s e n t s t h e length f r o m t h e b a s e o f t h e p e c t o r a l f l i p p e r to its tip. Pelvic l e n g t h r e p r e s e n t s t h e length of t h e pelvic f l i p p e r b e t w e e n t h e b a s e o f t h e tail a n d t h e t i p o f t h e m i d d l e digit. F i n a l l y , pelvic m a x w i d t h r e p r e s e n t s t h e w i d t h o f t h e s p r e a d - o u t pelvic f l i p p e r right at t h e b a s e o f t h e digital e x t e n s i o n s . M e a s u r e m e n t s w e r e t a k e n o n o n e f l i p p e r o n l y a n d it w a s a s s u m e d t h a t t h e s e c o n d flipper w a s i d e n t i c a l . T o t a l f l i p p e r a r e a w a s t h e r e f o r e 2 x ( p e c t o r a l flipper a r e a + pelvic f l i p p e r a r e a ) .  SL1  SL2  SL3  Total length  [m]  2.27 ± 0.02  2.29 ± 0.02  2.26 ± 0.02  Standard length (L)  [m]  1.83 ± 0.02  1.87 ± 0.02  1.92 ± 0.02  Frontal surface area  [m ]  0.149 ±  0.004  0.156 ±  0.004  0.167 ±  Total wetted surface area  [m ]  2.391 ± 0.066  2.551 ±  0.061  2.481 ± 0.059  137.3 ±  154.7 ± 8.9  150.8 ± 8.4  Volume  2  2  [1]  10.4  0.004  -  5.2 ± 0.2  5.1 ± 0.2  4.9 ± 0.2  Position of max thickness  [% of L]  44.3  42.8  45.8  CG position  [% of L]  57.4  55.6  51.6  Pectoral flipper area  [m ]  0.104  0.115  0.107  Pectoral length  [m]  0.58  0.60  0.60  Pectoral max width  [m]  0.23  0.24  0.24  -  3.23  3.13  3.32  Pelvic flipper area  [m ]  0.085  0.082  0.092  Pelvic length  [m]  0.45  0.46  0.46  Pelvic max width  [m]  0.28  0.25  0.29  Pelvic aspect ratio  -  2.38  2.53  2.26  [m ]  0.378  0.394  0.396  Fineness ratio  Pectoral aspect ratio  Total flipper area  2  2  2  19  Kinematics A total of 4 1 9 t u r n s w e r e f i l m e d f r o m A u g u s t 1 5  t h  to D e c e m b e r 3 , 2 0 0 3 . All t u r n s w e r e partially r d  u n p o w e r e d m a n o e u v r e s p e r f o r m e d w i t h a n o n - z e r o initial s p e e d (a m a n o e u v r e starting f r o m  a  resting position w a s n e v e r o b s e r v e d ) . In all 4 1 9 e v e n t s , t h e t h r e e a n i m a l s u s e d t h e s a m e g e n e r a l t u r n i n g t e c h n i q u e to p e r f o r m t h e 1 8 0 - d e g r e e s t u r n s . S o m e k i n e m a t i c p a r a m e t e r s f l u c t u a t e d b e t w e e n t u r n s , s u c h a s t h e rolling d e g r e e s , t h e d e g r e e s o f a b d u c t i o n ( m o v e m e n t a w a y f r o m t h e m i d l i n e o f t h e b o d y — Fish e t a l . , 2 0 0 3 ) o f t h e p e c t o r a l f l i p p e r s , a n d t h e d o r s a l a r c h i n g o f t h e b a c k b o n e , e t c . T h e animals were never observed performing  a ventrally  induced turn. T h e turning  technique  o b s e r v e d w a s in all r e g a r d s c o m p a r a b l e to t h e t u r n i n g t e c h n i q u e d e s c r i b e d by Fish et al. ( 2 0 0 3 ) f o r t h e C a l i f o r n i a s e a lion. T a b l e 3 p r e s e n t s t h e s e q u e n c e o f m o v e m e n t s t a k i n g  place during  the  m a n o e u v r e a n d d i v i d e s t h e t e c h n i q u e into 6 m a i n e v e n t s (or s e r i e s o f e v e n t s ) .  B e f o r e p e r f o r m i n g t h e t u r n i n g s e q u e n c e , t h e a n i m a l g l i d e d horizontally w i t h its d o r s a l s i d e t o w a r d s t h e s u r f a c e . T h e p l a n t a r f a c e o f t h e pectoral flippers w a s a p p l i e d a g a i n s t t h e v e n t r o - l a t e r a l s i d e o f t h e a n i m a l w h i l e g l i d i n g , a n d t h e pelvic flippers w e r e c o n t r a c t e d a n d held t o g e t h e r w i t h t h e i r plantar f a c e s in c o n t a c t . T h i s position m i n i m i s e d t h e inter-digital w e b of t h e pelvic f l i p p e r s . U p o n e n t e r i n g t h e t u r n , t h e a n i m a l p e r f o r m e d t h r e e m o v e m e n t s : 1) t h e h e a d w a s o r i e n t e d a n d e x t e n d e d t o w a r d s t h e inside o f t h e t u r n , 2) t h e p e c t o r a l flippers w e r e a b d u c t e d a n d 3) t h e a n i m a l rolled to orient its b a c k inside t h e t u r n ( F i g . 6 . 1 ) . T h e s e q u e n c e o f t h e s e t h r e e e v e n t s v a r i e d f r o m t u r n to t u r n a n d t h e y w e r e often performed simultaneously.  T h e m o v e m e n t o f t h e p e c t o r a l flippers w a s as f o l l o w s . F r o m t h e i r g l i d i n g p o s i t i o n , t h e s e a lions rotated t h e i r flippers o u t w a r d s a n d b r o u g h t t h e m a w a y f r o m t h e m i d l i n e o f t h e i r b o d i e s ( a b d u c t i o n , Figs  6.2  and  6.3).  At  the  end  of  the  abduction,  the  pectoral  flippers  were  approximately  p e r p e n d i c u l a r t o t h e m i d l i n e o f t h e b o d y a n d r e m a i n e d s t a t i o n a r y until t h e a n t e r i o r p a r t o f t h e b o d y ( h e a d , n e c k , a n d t o r s o ) s t a r t e d t o exit t h e t u r n ( F i g . 6.4). D u r i n g t h e c u r v e d p a r t o f t h e t r a j e c t o r y , t h e b o d y w a s e x t e n d e d a n d a r c h e d d o r s a l l y in a U - s h a p e p o s i t i o n ( F i g s 6 . 4 a n d 6 . 5 ) . T h e interdigital w e b of t h e pelvic flippers w a s t h e n e x t e n d e d (thus i n c r e a s i n g t h e i r s u r f a c e a r e a ) w i t h t h e  20  v e n t r a l s i d e s f a c i n g t h e o u t s i d e of t h e t u r n . A s t h e a n t e r i o r b o d y s t a r t e d to r e g a i n a s t r a i g h t p o s i t i o n , t h e a n i m a l p e r f o r m e d a p e c t o r a l flipper s t r o k e a n d a c c e l e r a t e d o u t o f t h e t u r n ( F i g s 6.5 a n d 6 . 6 ) . Finally, t h e pectoral flippers p r e v i o u s l y held a w a y f r o m t h e b o d y ' s m i d l i n e w e r e b r o u g h t b a c k a l o n g t h e a n i m a l ' s v e n t r o - l a t e r a l s u r f a c e (i.e. a d d u c t i o n ) .  T h e s t r o k e m o v e m e n t o f t h e p e c t o r a l flippers w a s o r i e n t e d d o w n w a r d s a n d b a c k w a r d s , a n d t h e f r o n t e d g e s of t h e flippers w e r e r o t a t e d i n w a r d s t o r e p o s i t i o n t h e p l a n t a r f a c e of t h e p e c t o r a l flippers a g a i n s t t h e b o d y of t h e a n i m a l . T h i s m o t i o n w a s c o m p o s e d o f t w o p h a s e s a s d e s c r i b e d by F e l d k a m p ( 1 9 8 7 a ) : 1) t h e p o w e r p h a s e (forceful d o r s o - v e n t r a l a d d u c t i o n , w h i c h e n d s in a full e x t e n s i o n o f t h e p e c t o r a l flippers b e l o w t h e b o d y ) a n d 2) t h e p a d d l e p h a s e (flippers o r i e n t e d ' b r o a d s i d e to t h e f l o w ' and brought backwards and upwards towards the body).  T h e m i d l i n e o f t h e b o d y o f t h e a n i m a l r e g a i n e d a s t r a i g h t position b e f o r e t h e e n d o f t h e p e c t o r a l f l i p p e r s t r o k e . A s t h e p o w e r p h a s e w a s p e r f o r m e d , t h e b o d y rolled b a c k t o r e o r i e n t t h e d o r s a l s u r f a c e u p , t h e h e a d r e g a i n e d its s t r a i g h t f o r w a r d  orientation, and the neck remained extended.  Lastly, t h e pelvic f l i p p e r s w e r e slowly r o t a t e d a n d b r o u g h t b a c k t o g e t h e r in t h e gliding  position  d e s c r i b e d a b o v e ( F i g . 6 . 6 ) . S o m e t i m e s t h e a n i m a l s d i d not roll b a c k c o m p l e t e l y a n d r e m a i n e d at a n angle as they glided out of the turn.  T h e t r a j e c t o r y o f t h e n o s e o f t h e a n i m a l differed f r o m t h e rest of t h e b o d y . W h i l e t h e t r a j e c t o r y o f t h e s h o u l d e r , C G a n d hips w e r e s m o o t h (i.e. a linear g l i d e into t h e t u r n , f o l l o w e d circular o r elliptical t u r n , f o l l o w e d b y a linear e x i t ) , t h e trajectory o f t h e n o s e w a s m o r e irregular. First, it w a s d i s p l a c e d a n d e x t e n d e d into t h e t u r n a s t h e a n i m a l e n t e r e d t h e m a n o e u v r e (as d e s c r i b e d a b o v e ) , w h i c h resulted in a n a n g u l a r trajectory. S e c o n d , w h i l e t h e a n i m a l r e - a c c e l e r a t e d a t t h e e n d o f t h e t u r n , t h e trajectory o f t h e n o s e d i d not f o l l o w t h e g e n e r a l d i r e c t i o n o f t h e rest of t h e b o d y . I n s t e a d t h e n o s e a p p e a r e d t o initially f o l l o w a path leading t o w a r d s t h e inside o f t h e t u r n b e f o r e c h a n g i n g its c o u r s e a n d t a k i n g t h e d i r e c t i o n f o l l o w e d by t h e rest o f t h e b o d y ( F i g . 1 0 ) . T h i s c h a n g e o f c o r r e s p o n d e d w i t h t h e o n s e t of t h e a d d u c t i o n o f t h e p e c t o r a l f l i p p e r s .  trajectory  21  T h e radius o f t h e m i n i m u m c i r c u m c i r c l e t h a t p a s s e s t h r o u g h e a c h b o d y m a r k e r , including t h e n o s e , w a s m e a s u r e d in 31 t u r n s . T h i s r a d i u s , w h i c h m e a s u r e d t h e d e g r e e of d o r s a l c u r v a t u r e d u r i n g t h e t u r n , r a n g e d f r o m 0 . 2 7 L (i.e. e x p r e s s e d relative to t h e a n i m a l ' s b o d y l e n g t h — L) t o 0 . 3 9 L w i t h a n a v e r a g e of 0 . 3 2 L ( w h i c h c o r r e s p o n d s to a r a n g e o f 0 . 5 1 m t o 0 . 6 9 m w i t h a n a v e r a g e o f 0 . 6 m ) . T h e radii o f t h e 31 t u r n s in w h i c h b o d y c u r v a t u r e w a s m e a s u r e d v a r i e d b e t w e e n 0 . 1 7 L a n d 0 . 3 6 L w i t h a n a v e r a g e o f 0 . 2 7 L ( w h i c h c o r r e s p o n d s to a r a n g e of 0 . 3 2 m to 0 . 6 4 m w i t h a n a v e r a g e of 0 . 5 m ) . F i g . 7 illustrates t h e relationship b e t w e e n t h e relative t u r n i n g radius a n d t h e relative d o r s a l c u r v a t u r e . T h e larger t h e t u r n i n g r a d i u s , t h e s t r a i g h t e r t h e b o d y (linear r e g r e s s i o n , F  3 0  = 18.27, p<0.001).  1.  ! Plexiglas sheet  4.  Fig. 6: Sequence of movements based on turn H128 performed by SL3. Arrows indicate the principal movements of the animal on each frame. 1. The head is oriented towards the inside of the turn and the pectoral flippers are abducted. 2. The body starts flexing dorsally and rolls. 3. The body flexion continues, the abduction of the pectoral flippers reaches an end, the body rolls, and the interdigital web of the pelvic flippers starts to unfold. 4. The roll has stopped, the body is maximally arched dorsally, the digits of the pelvic flipper open. 5. As the body regains a straight position, the pectoral flippers are adducted, the interdigital web of pelvic flippers is spread out. 6. The body regains a straight position, the pectoral flippers reach the last stage of the power stroke, and the pelvic flippers return to their gliding position.  23  T a b l e 3: Sequence of movements performed by SU3 during a 180 degrees turn. Each row corresponds to a turn. The numbers between 1 and 12 in the tables describe the sequence of movements. When several actions take place at the same time, they get the same number and are highlighted in light or dark grey. " N A " signifies that a movement happened out of the field of view of the camera or that it could not be identified clearly. In that case, it is ignored from the sequence. The vertical blanks delimit shorter sequences (of 2 or 3 movements) that are repeatedly distinct from the rest of the sequence. A dashed line in the header between two sections indicates that these two sections tend to be distinct but not always. H i : movement of the head inside the turn; A b : start of the abduction of the pectoral flippers; RQ: start of the roll of the body; P : opening of the interdigital web of the pelvic flippers; F : start of the dorsal flexion; A b i : end of the abduction of the pectoral flippers; R : maximum roll; F : minimum radius of curvature of the flexed body; A d : start of the adduction of the pectoral flippers; F : body back in a straight position; A d i : end of the adduction of the pectoral flipper; P : the plantar surfaces of the pelvic flippers are back in contact, and the inter-digital web closes gradually afterwards. 0  start  start  M A X  m a x  0  e n d  e n d  Turn  Hi  Ab  H68 H71 H73 H74 H75 H77 H78 H84 H89 H92 H93 H95 H96 H97 H98 H99 H101 H103 H104 H105 H106 H107 H108 H109 H110 H113 H114 H115 H116 H117 H128  2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1  1 1 1 1 1 1 1 1 1 1 1 1 1 1  0  1 1 1  1 1 1 1 1 1 1 1  H9B 1 1 2 NA  HSE 1 NA  N H HSH 1 1  1 1 1  Ro  Pstart  Pstart  Ab,  p "max  3 2 2 2 2 2 2 2 2 2 2  4 3 NA NA NA 4 4 4 4 4 NA 3 NA 3 2 3 3 4 4  5 3 3 3 3 3 3 3 3 3 3 3 2 2 2 4 2 3 5 3 4 4 4  6 4 4 4 4 5 5 5 5 5 4 4 3 4 3 5 4 5 6 4 5 5 5 3 4 4 4 5 5 4 5  7 5 5 5 5 6 6 6 5 6 5 4 3 5 3 6 5 5 6 4 5 5 5 4 5 5 5 6 6 5 6  2 1  mem 2 HHflH 2 2 2 2 3 3 2 2 2 2 3 2 2  3 NA 4 NA NA  HH NA 4  3 3 3 3  ^.  NA 4  3 3  ^max  Ad  0  8 6 6 6 6 7 7  9 6 6 7 7 7 7 7 7  HH 6  6 6 4 6 5 7 6 6 7 5 6 6 6 5 6 7 6 7 8 6 7  7 6 5 5 6 4 7 6 6 7 5 6 6 6 5 6 6 6 7 7 6 7  Pend  Ad,  Pend  10 7  10 8 7 9 8 9 8 9 8 9 7 7 6 7 6 9 8 8 8 7 8  11 9 8 10 9 10 9 10 9 10 8 8 7 8 7 10 9 9 9 8 9 8 9 8 9  HH 8 8 8 8 8 8 8 7 7 6 7 6 8 7 7 8 6 7 7 6 7 8 7 8 9 7 8  HH 8 7 8 9 8 9 10 8 9  10  9 10 11 9 10  24  Table 3 (continued): Sequence of movements performed by SL2. Turn  Hi  Ab  Ro  Pstart  Fstart  Ab,  "max  ^max  Ad  Fend  Ad,  T007  1  2  3  NA  4  5  NA  7  6  8  9  10  T012  1  NA  2  NA  3  4  5  6  7  8  8  NA  0  0  Pend  T080  1  2  2  NA  3  4  4  6  5  7  7  8  T081  1  1  1  NA  2  3  3  5  4  6  6  7  T108  2  1  1  NA  3  4  5  7  6  8  8  9  T109  2  1  1  NA  3  4  5  7  6  8  8  9  T111  3  1  2  4  5  6  7  9  8  10  10  11  T112  2  1  1  NA  3  4  5  7  6  8  NA  9  T 1i|3  1  1  2  NA  3  4  5  7  6  8  8  9  T114  3  1  2  6  4  5  7  9  8  10  10  11  Tints  3  1  2  5  4  6  6  8  7  9  9  10  Ttf6  1  1  2  4  3  5  5  7  6  8  9  10  T117  2  1  2  5  3  4  6  8  7  9  10  11  T118  1  1  1  3  2  4  4  6  5  7  8  9  T120  1  1  1  3  2  4  4  6  5  7  8  9  T122  2  1  1  4  6  5  7  8  9  T123  2  1  1  4  • H3 i  4 5  5  7  6  8  8  9  1  4  3  5  5  7  6  8  9  10  2  1  T125  1  1  1  3  2  4  4  6  5  7  8  9  T126  2  1  1  4  3  5  6  8  9  10  T127  2  1  1  4  3  5  5  IHI  7  6  6  7  8  9  T129  2  1  1  4  3  5  5  7  6  8  8  9  T130  2  1  1  4  3  5  5  7  6  8  8  9  T131  2  1  1  NA  3  4  4  6  7  8  T132  2  1  1  NA  3  4  5  HBfl 7  5 6  8  9  10  T133  2  1  1  3  3  4  5  7  6  8  9  10  T134  1  1  1  NA  2  3  3  5  4  6  7  8  T136  1  1  1  2  2  3  3  5  4  6  7  8  T138  3  1  2  4  4  5  5  7  6  8  9  10  T139  2  1  1  4  3  5  5  7  6  8  9  10  T124  Table 3 (continued): Sequence of movements performed by SL1. Turn  H,  Ab  Y005  i  i  Y006  1  Y063  1  Y064  1  Y066  1  Y067  1  R  0  P.t.  0  2  1  2 1  2  NA  2  1  1 1  2 1  F„.„  Ab,  R„»,  Fm.«  Ad  3  3  4  5  6  7  NA  3  4  rt  HflflHH N  5  4  6 5  7  6  F.  8 7  7  Ad,  n d  8  P.  10  8  9  10  11  8  8  8  n d  9  9  3  4  5  A  2  3  3  5  4  6  6  7  NA  3  4  5  6  6  7  8  9  ygg/gggg/l  6  0  Y068  1  1  Y069  2  1  Y070  1  NA  2  4  Y072  2  1  1  4  Y073  2  Y074  1  1  2  4  3  5  6  7  7  8  9  10  Y076  1  2  2  4  3  5  5  6  6  7  8  9  Y097  2  1  2  3  3  4  4  5  5  6  7  8  Y099  1  NA  1  3  2  4  4  5  5  6  7  Y100  1  NA  1  NA  2  3  3  Y101  1  1  1  NA  2  3  3  Y102  2  1  1  4  3  1  3  N  A  4  5  5  6  7  8  5  6  7  8  9  10  11  3  5  3  5  5  3  3  5  4  4  • ;;.  5  7 NA  5  6  6  6 3  6  8  BLHHHB 7  8  4  4  8  7  4  4  7  8  9  7  8  9  10  11  8  5  6  5  6  7  9  10  11 8  Y103  1  1  NA  2  3  Y104  2  1  1  4  3  5  5  6  6  5 7  6 7  Y117  2  1  2  3  3  4  4  5  5  6  NA  7  7 7_  25  0.41  0.37 ]• CO  «J  0.33  l  3 U  >  o  CO 0.29 h  0.25  0.25  0.20  0.15  0.40  0.35  0.30  Turning radius [BL]  Fig. 7 : of  three  R e l a t i o n s h i p b e t w e e n t u r n i n g radius a n d t h e d e g r e e of b o d y Steller  sea  lions  performing  a  180  degrees  turn.  31  curvature turns  are  r e p r e s e n t e d h e r e . B o d y c u r v a t u r e is e x p r e s s e d as t h e radius of t h e c i r c u m c i r c l e that passes through  t h e 4 b o d y m a r k e r s : n o s e , s h o u l d e r s , C G , a n d hips. All  measurements  expressed  are  c o m p e n s a t e for size d i f f e r e n c e s .  relative  to  each  animal's  body  length  to  26  Kinetics O u t of t h e 4 1 9 t u r n s t h a t w e r e f i l m e d w i t h t h e 3 test a n i m a l s , 195 o c c u r r e d directly u n d e r t h e Plexiglas s h e e t a n d w e r e kept f o r f u r t h e r a n a l y s i s . In e a c h a n a l y s e d t u r n , I m e a s u r e d t u r n i n g r a d i u s , s p e e d , a n g u l a r s p e e d , a c c e l e r a t i o n , s l i p p a g e , rolling t i m e , a n d m a n o e u v r i n g t i m e ( 6 4 t u r n s for S L 1 , 70 for S L 2 , and 61 for S L 3 ) .  T h e t u r n i n g s e q u e n c e w a s p e r f o r m e d in 1 . 6 5 ± 0 . 1 7 s f o r S L 1 , 1 . 7 4 ± 0 . 2 0 s f o r S L 2 , a n d  1.32±0.13s  for S L 3 . T h e s e d i f f e r e n c e s in t u r n i n g d u r a t i o n w e r e significant a m o n g all a n i m a l s ( o n e - w a y A N O V A ; F = 8 0 . 2 , p < 0 . 0 0 0 1 ) . I n t e r - a n i m a l v a r i a t i o n s w e r e o b s e r v e d o n all m e a s u r e d p a r a m e t e r s , e x c e p t for 2  t h e d e c e l e r a t i o n o f t h e C G for w h i c h d a t a w e r e often m i s s i n g b e c a u s e t h e a b d u c t e d pectoral flippers covered the marker (Table 4).  T h e i n s t a n t a n e o u s s p e e d d a t a plotted a g a i n s t t i m e p r o d u c e d a t y p i c a l V - s h a p e d c u r v e in all t u r n s r e c o r d e d ( s e e F i g . 8 ) . T h e s p e e d of t h e a n i m a l s w h i l e gliding b e f o r e t h e first m o v e m e n t o f t h e t u r n w a s c o n s t a n t o r slightly d e c r e a s i n g . T h i s p l a t e a u w a s f o l l o w e d by a p e r i o d o f d e c e l e r a t i o n , w h i c h c o r r e s p o n d e d to t h e start of t h e t u r n i n g m o v e m e n t s (i.e. m o v e m e n t o f t h e h e a d inside t h e t u r n ; start of t h e a b d u c t i o n o f t h e pectoral f l i p p e r s ; start o f t h e roll o f t h e b o d y ) . T h e d e c e l e r a t i o n of t h e c e n t r e o f g r a v i t y s t o p p e d at o r after t h e t i m e o f m i n i m u m  roll, b e f o r e t h e start of t h e  flipper  a d d u c t i o n . I m m e d i a t e l y f o l l o w i n g this period o f d e c e l e r a t i o n , t h e s p e e d r e a c h e d a m i n i m u m f o r a s h o r t d u r a t i o n b e f o r e i n c r e a s i n g a g a i n . T h e a n i m a l s t a r t e d a c c e l e r a t i n g j u s t prior to o r a t t h e o n s e t o f t h e flipper a d d u c t i o n . J u s t b e f o r e t h e e n d o f t h e flipper s t r o k e , t h e s p e e d o n c e a g a i n a t t a i n e d a p l a t e a u o f c o n s t a n t o r slightly d e c r e a s i n g s p e e d . A t this point in t i m e , t h e m i d l i n e o f t h e b o d y h a d not y e t r e g a i n e d a fully straight p o s i t i o n .  W i t h i n a t u r n , t h e s p e e d profiles o f t h e different b o d y parts s h o w e d s o m e t e m p o r a l v a r i a t i o n s . T h e a n t e r i o r part of t h e b o d y ( r e p r e s e n t e d by t h e s h o u l d e r m a r k e r ) d e c e l e r a t e d f a s t e r t h a n t h e m i d d l e a n d p o s t e r i o r parts ( r e p r e s e n t e d by C G a n d t h e hip m a r k e r s r e s p e c t i v e l y ) ( T a b l e 4 a n d F i g . 9 ) . T h e overall r a n g e of d e c e l e r a t i o n o f t h e s h o u l d e r m a r k e r w a s f r o m - 0 . 2 7 m / s  2  to - 5 . 1 8 m / s  average - 2 . 1 9 m / s  2  w i t h a n a v e r a g e of -  2  ( ± 0.84); the C G ranged from - 0 . 3 9 m / s  2  to - 4 . 3 7 m / s  2  with an  27  1.48m/s  2  ( ± 0 . 8 9 ) ; t h e hips r a n g e d f r o m - 0 . 2 5 m / s to - 3 . 6 3 m / s w i t h a n a v e r a g e of - 1 . 6 4 m / s 2  2  2  (±  0.79) ( T a b l e 4 ) .  M i n i m u m s p e e d w a s a t t a i n e d slightly b e f o r e t h e m i d d l e o f t h e  180 degrees trajectory  of each  m a r k e r . C o n s e q u e n t l y , t h e s h o u l d e r s w e r e t h e first to attain m i n i m u m s p e e d , c l o s e l y f o l l o w e d by t h e C G , w h i c h w a s f o l l o w e d by t h e hips. A s t h e a n i m a l e x i t e d t h e t u r n , t h e s h o u l d e r s a n d t h e C G rea c c e l e r a t e d a t a s i m i l a r rate, w h i l e t h e a c c e l e r a t i o n o f t h e hips w a s c o n s i d e r a b l y h i g h e r . T h e r a n g e of a c c e l e r a t i o n o f t h e s h o u l d e r m a r k e r w a s f r o m 0 . 4 8 m / s to 6 . 6 6 m / s w i t h a n a v e r a g e 3 . 2 9 m / s 2  2  1.18); t h e C G r a n g e d f r o m 0 . 4 1 m / s  2  to 6 . 5 6 m / s  ranged from 0 . 5 7 m / s  2  with an average of 5 . 0 0 m / s  2  to 1 1 . 9 8 m / s  2  with an average of 3 . 0 0 m / s  2  (±  ( ± 1.22); t h e hips  2  ( ± 2.26) (Table 4). A s noted  2  a b o v e , t h e i n s t a n t a n e o u s s p e e d o f t h e t h r e e m a r k e r s r e a c h e d a c o m m o n p l a t e a u at t h e e n d of t h e turn. D u r i n g t h e t u r n , o n e c o m p o n e n t of t h e a c c e l e r a t i o n v e c t o r w a s parallel t o t h e v e l o c i t y (tangential  acceleration)  and  the  other  was  perpendicular  to  it  (normal  vector  acceleration).  Each  c o m p o n e n t b e h a v e d differently ( F i g . 9) a n d f o l l o w e d t h e t e m p o r a l v a r i a t i o n s of t h e b o d y parts.  T h e p o l y n o m i a l c u r v e d e s c r i b i n g t a n g e n t i a l a c c e l e r a t i o n c l o s e l y f o l l o w e d t h e v a r i a t i o n s in t h e s p e e d profile. A s t h e a n i m a l g l i d e d b e f o r e e n t e r i n g t h e m a n o e u v r e , t h e v a l u e o f t a n g e n t i a l a c c e l e r a t i o n w a s slightly n e g a t i v e a n d c l o s e to z e r o . A s t h e a n i m a l rolled into t h e t u r n a n d a b d u c t e d its pectoral flippers, t h e t a n g e n t i a l a c c e l e r a t i o n o f t h e s h o u l d e r s a n d C G f u r t h e r d e c r e a s e d until it r e a c h e d a m i n i m u m a p p r o x i m a t e l y w h e n t h e pectoral flippers a t t a i n e d their full a b d u c t e d p o s i t i o n . It  then  c a m e b a c k t o z e r o w h e n t h e s p e e d s of both b o d y parts r e a c h e d their m i n i m u m . A s s p e e d i n c r e a s e d , t h e t a n g e n t i a l a c c e l e r a t i o n b e c a m e positive a n d r e a c h e d a m a x i m u m p a r t w a y t h r o u g h t h e pectoral flipper s t r o k e b e f o r e c o m i n g b a c k c l o s e t o a nil — or slightly n e g a t i v e — v a l u e a s t h e a n i m a l g l i d e d o u t of t h e t u r n . T h e hips s t a r t e d d e c e l e r a t i n g later, w h e n t h e  body started  bending and  the  trajectory o f t h e hips d e v i a t e d f r o m t h e trajectory o f t h e o t h e r t w o m a r k e r s . T h e o n s e t o f t h e hips d e c e l e r a t i o n c o r r e s p o n d e d t o t h e m o v e m e n t s o f t h e pelvic flippers. It r e m a i n e d n e g a t i v e t h r o u g h t h e first half of t h e m a n o e u v r e a n d r e a c c e l e r a t e d a b r u p t l y a s t h e hips t r a j e c t o r y " c u t t h r o u g h " t h e o t h e r  28  t r a j e c t o r i e s a n d t h e b o d y of t h e a n i m a l s t r a i g h t e n e d . T h e m a x i m u m t a n g e n t i a l a c c e l e r a t i o n of t h e hips w a s r e a c h e d j u s t b e f o r e t h e e n d o f t h e p o w e r p h a s e . T h e t a n g e n t i a l a c c e l e r a t i o n o f all t h r e e m a r k e r s p e a k e d after t h e c u r v e d portion o f their r e s p e c t i v e t r a j e c t o r y .  T h e n o r m a l a c c e l e r a t i o n h a d a different profile t h a n t h e t a n g e n t i a l a c c e l e r a t i o n . D u r i n g t h e linear glide p r e c e d i n g t h e m a n o e u v r e , t h e n o r m a l a c c e l e r a t i o n o f t h e s h o u l d e r a n d c e n t r e o f gravity w a s c l o s e to z e r o . It t h e n i n c r e a s e d w h e n t h e a n i m a l o r i e n t e d its h e a d into t h e t u r n , s t a r t e d rolling a n d a b d u c t i n g t h e p e c t o r a l f l i p p e r s , a n d r e a c h e d a m a x i m u m j u s t after t h e s t a r t o f t h e p o w e r p h a s e . T h i s c o r r e s p o n d e d t o a point in t h e m a n o e u v r e t h a t w a s slightly after t h e m i d d l e o f t h e 180 d e g r e e s t u r n . Finally, n o r m a l a c c e l e r a t i o n of t h e s h o u l d e r a n d c e n t r e o f g r a v i t y q u i c k l y c a m e b a c k t o a nil v a l u e at t h e e n d of t h e p o w e r p h a s e . T h e n o r m a l a c c e l e r a t i o n o f t h e hips s t a r t e d a t t h e b e g i n n i n g of t h e d o r s a l f l e x i o n o f t h e b o d y a n d r e a c h e d its m a x i m u m h a l f w a y t h r o u g h t h e p o w e r p h a s e . It c a m e b a c k to a z e r o v a l u e a s t h e b o d y r e g a i n e d a straight p o s i t i o n . A s w i t h t a n g e n t i a l a c c e l e r a t i o n , n o r m a l a c c e l e r a t i o n f o l l o w e d t h e t e m p o r a l v a r i a t i o n s o f t h e d i f f e r e n t b o d y parts (i.e. t h e s h o u l d e r s r e a c h e d their m a x i m u m v a l u e first, f o l l o w e d by t h e C G , a n d t h e n t h e h i p s ) .  T h e m a x i m u m v a l u e o f n o r m a l a c c e l e r a t i o n w a s s y s t e m a t i c a l l y g r e a t e r t h a n t h e m a x i m u m v a l u e of t a n g e n t i a l a c c e l e r a t i o n f o r all t h r e e a n i m a l s a n d all t h r e e m a r k e r s . F u r t h e r m o r e , t h e  maximum  normal acceleration always preceded the m a x i m u m of tangential acceleration for each marker (Fig. 9). A t t h e b e g i n n i n g a n d e n d o f t h e profiles, t h e a c c e l e r a t i o n c u r v e s o c c a s i o n a l l y " o v e r s h o t " c r e a t i n g seemingly another m a x i m u m or m i n i m u m . This w a s an artefact of the calculation technique and depended o n the shape of the 6 second derivative).  t h  degree polynomial fitted to the position d a t a (for which I took the  29  • Trajectory of t h e s h o u l d e r  • Trajectory of the centre of gravity • Trajectory of the hips  Origin  3.9 • Shoulder  • Centre of gravity • Hips  :  «  •••  3.5 ••••  7*3.1  • • ••:  S CL  in  2.7  :••• • • •  • • •• a  •  2.3  1.9  0.4  0.8  Time [s]  1.2  1.6  2.0  F i g . 8:Typical t r a j e c t o r y a n d s p e e d profile o f t h e s h o u l d e r , c e n t r e of g r a v i t y , a n d h i p s m a r k e r s o f a Steller s e a lion p e r f o r m i n g a 180 d e g r e e t u r n . T h e d a s h e d lines delimit t h e b o u t s o f c o n s t a n t s p e e d , f r o m t h e b o u t s o f d e c e l e r a t i o n a n d acceleration o n both charts.  3.9 • Shoulder • Centre of gravity  • « ••ni' ••••• • •  3.5 . • Hips  -SU  E  1  3.1  • ••• •  • ••••  &2.7  •••• . •  •• ••• •  2.3  1.9  • • • • • •• * •••  • •  •  Fig. 9: T a n g e n t i a l a n d n o r m a l a c c e l e r a t i o n profiles o f t h e s h o u l d e r , t h e c e n t r e o f g r a v i t y , a n d hips m a r k e r s o f a Steller s e a lion p e r f o r m i n g a 1 8 0 d e g r e e t u r n in c o r r e l a t i o n w i t h its s w i m m i n g s p e e d . T h e d a s h e d lines r e p r e s e n t t a n g e n t i a l a c c e l e r a t i o n a n d t h e plain lines a r e n o r m a l a c c e l e r a t i o n .  T a b l e 4: Mean kinetic parameters for the SL3, SL2, and SL1. The different letters and grey tones (white, grey, dark grey) represent a significant difference between each animal at alpha=0.05.  SL1  SL2  SL3  2.69  a  2.93  b  2.92  b  3.22  b  3.08  b  3.77  a  Rolling time [s]  0.76  b  0.74  b  0.64  a  T u r n duration [s]  1.65  0  1.74  b  1.32  a  Shoulders  0.32  b  0.31  b  a  CG  0.32  b  0.30  b  0.26 0.27  Hips  0.33  b  0.33  b  0.26  a  Shoulders  -1.75  a  -2.40  b  -2.43  b  CG  -1.31  Hips  -1.20  a  -1.84  b  -1.89  b  Shoulders  2.50  c  3.39  b  3.96  a  CG  2.70  b  3.01  Hips  4.11  b  3.86  In s p e e d  [m/s]  Out s p e e d  [m/s]  T u r n i n g radii [BLs] a  Deceleration [m/s ] 2  -1.48  -1.65  Acceleration [m/s ] 2  a b  b  3.29  a  7.12  a  32  DISCUSSION Morphology A series o f r e c e n t articles h a v e illustrated t h e conflict b e t w e e n stability a n d m a n o e u v r a b i l i t y  in  a c t i v e , m o b i l e individuals ( F i s h , 1 9 9 7 ; F i s h , 2 0 0 2 ; Fish et a l . , 2 0 0 3 ; W e i h s , 2 0 0 2 ) . Stability, b y d e f i n i t i o n , is a p r o p e r t y of t h e b o d y t h a t c r e a t e s f o r c e s t h a t r e s t o r e its original c o n d i t i o n w h e n d i s t u r b e d f r o m a c o n d i t i o n of e q u i l i b r i u m . In c o n t r a s t , m a n o e u v r a b i l i t y is t h e c a p a c i t y t o  rapidly  c h a n g e d i r e c t i o n , w h i c h m e a n s q u i c k l y c r e a t i n g a n d m a i n t a i n i n g highly u n b a l a n c e d f o r c e s .  Stability is a d v a n t a g e o u s w h e n a n individual is c o n s t a n t l y a n d s t e a d i l y m o v i n g f o r a n e x t e n d e d period of t i m e , e . g . d u r i n g m i g r a t i o n , o r d u r i n g trips to f o r a g i n g g r o u n d s . In t h e s e c i r c u m s t a n c e s , t h e individual tries t o o p t i m i s e its e n e r g e t i c e x p e n d i t u r e s in relation to d i s t a n c e c o v e r e d in o r d e r to r e a c h its d e s t i n a t i o n as c o s t - e f f e c t i v e l y as p o s s i b l e . T o d o s o , it m a k e s u s e of s t r u c t u r e s t h a t d e c r e a s e t h e e n e r g e t i c c o s t of s t e a d y l o c o m o t i o n , s u c h a s k e e l s , rigid d o r s a l f i n s , a n d / o r lateral c o m p r e s s i o n of t h e b o d y . T h e s e m o r p h o l o g i c a l c h a r a c t e r i s t i c s resist roll a n d s i d e t o s i d e m o v e m e n t s , w h i c h o t h e r w i s e w o u l d h a v e to be c o n t r o l l e d by m u s c u l a r activity a n d w o u l d i n d u c e c o s t s . A l s o , control surfaces located far from, a n d posterior to, the centre of gravity (CG) possess more leverage to c o r r e c t f o r u n n e c e s s a r y a n d ' w a s t e f u l ' m o v e m e n t s . O t h e r a d a p t a t i o n s t h a t m i n i m i s e d r a g a n d m a x i m i z e t h r u s t p r o d u c t i o n include r e d u c e d m o t i o n of t h e c o n t r o l s u r f a c e s , a n t e r i o r p l a c e m e n t of t h e c e n t r e o f g r a v i t y , r e d u c e d flexibility o f t h e b o d y , isolation o f t h e t h r u s t p r o d u c i n g unit f r o m t h e rest o f t h e b o d y , a n d a l u n a t e c a u d a l fin w i t h a high a s p e c t ratio ( l a r g e s p a n a n d relatively s m a l l c o r d ) ( B l a k e , 2 0 0 4 ; F i s h , 1 9 9 7 ; F i s h , 2 0 0 2 ; Fish et a l . , 2 0 0 3 ) .  In c o n t r a s t t o stability, m a n o e u v r a b i l i t y is beneficial w h e n e s c a p i n g a f a s t p r e d a t o r o r w h e n t r y i n g to c a p t u r e a n e l u s i v e p r e y ( H o w l a n d , 1 9 7 4 ) . In t h e s e s i t u a t i o n s , e n e r g y c o n s e r v a t i o n is less crucial than  k i n e m a t i c p e r f o r m a n c e , b e c a u s e a) b e i n g c a u g h t by a p r e d a t o r is not a n o p t i o n a n d  p r e d a t o r y s u c c e s s d e p e n d s o n t h e p r e d a t o r ' s ability to o u t - m a n o e u v r e its p r e y .  b)  33  Steller s e a lions ( a n d otariids in g e n e r a l ) d i s p l a y m o r p h o l o g i c a l c h a r a c t e r i s t i c s of a v e r y u n s t a b l e b o d y d e s i g n . T h e y h a v e highly m o b i l e c o n t r o l s u r f a c e s p l a c e d a t t h e i r c e n t r e s o f g r a v i t y , r o u n d e d c r o s s - s e c t i o n s ( w i t h t h e e x c e p t i o n of t h e h e a d s a n d t h e hips t h a t a r e b o t h slightly d o r s o - v e n t r a l l y c o m p r e s s e d ) , a n d v e r y flexible b o d i e s . T h e c e n t r e of g r a v i t y is p o s i t i o n e d past t h e m i d d l e of t h e b o d y ( T a b l e 2 ) , slightly a n t e r i o r to t h e insertion of t h e trailing e d g e o f t h e p e c t o r a l f l i p p e r s . T h e s e m o r p h o l o g i c a l f e a t u r e s c o n t r a s t m a r k e d l y w i t h t h e list o f c h a r a c t e r i s t i c s a s s o c i a t e d w i t h  stability  presented above.  A n u n s t a b l e b o d y d e s i g n likely p r o v i d e s a n u m b e r o f e c o l o g i c a l a d v a n t a g e s f o r S t e l l e r s e a lions. Domenici  (2003)  argues that the  body  design of  an organism  is highly  influenced  by  their  e n v i r o n m e n t a n d life history traits ( e . g . t h u n n i f o r m s , s u c h a s t u n a s , inhabit p e l a g i c m a r i n e habitat a n d h a v e o n e o f t h e m o s t s t a b l e f u n c t i o n a l d e s i g n — B l a k e , 2 0 0 4 ) . S t e l l e r s e a lions, o n t h e o t h e r h a n d , a r e a m p h i b i o u s c r e a t u r e s t h a t s p e n d a s u b s t a n t i a l a m o u n t o f t i m e o n land (particularly d u r i n g t h e b r e e d i n g s e a s o n ) a n d , w h e n in t h e w a t e r , a r e m o s t l y f o u n d f r o m n e a r s h o r e t o t h e e d g e o f t h e c o n t i n e n t a l s h e l f ( L o u g h l i n et a l . , 1 9 8 7 ; N a t i o n a l M a r i n e Fisheries S e r v i c e , 1 9 9 2 ) . S t r o n g a n d m o b i l e pectoral flippers a r e a n a d v a n t a g e o n land b e c a u s e t h e y s u p p o r t t h e a n i m a l ' s w e i g h t a n d a l l o w g r e a t e r mobility. O t a r i i d s a r e c a p a b l e o f agile q u a d r u p e d a l l o c o m o t i o n o n land ( E n g l i s h , 1 9 7 6 ) . In c o m p a r i s o n , p h o c i d s t h a t h a v e less d e v e l o p e d p e c t o r a l flippers a n d s w i m u s i n g t h e i r p e l v i c flippers and  body oscillations, are awkward  and slow on  l a n d . S e a lions u s e t h e i r  o n - l a n d agility  to  r e p r o d u c e , rest, a n d e s c a p e f r o m m a r i n e p r e d a t o r s . M o r e s p e c i f i c a l l y , m a l e s e a lions a r e highly territorial d u r i n g t h e b r e e d i n g s e a s o n a n d u s e their terrestrial mobility t o e s t a b l i s h territories a n d fight-off c o m p e t i t o r s . T h e i r d o r s a l flexibility a l l o w s t h e m to k e e p t h e i r t o r s o a n d h e a d in a n upright position to w a t c h o v e r territories. Finally, Steller s e a lions u s e t h e i r m o b i l i t y o n land to c l i m b r o c k s o u t of r e a c h o f m a r i n e p r e d a t o r s a n d find a r e a s s h e l t e r e d f r o m s t o r m s .  T h e u n s t a b l e b o d y d e s i g n of Steller s e a lions is a l s o a d v a n t a g e o u s in t h e a q u a t i c  environment.  Steller s e a lions a r e o p p o r t u n i s t i c p r e d a t o r s t h a t f o r a g e o n a w i d e v a r i e t y o f p r e y s p e c i e s w i t h o u t a c l e a r p r e f e r e n c e f o r o n e particular kind ( R i e d m a n , 1 9 9 0 ; Sinclair a n d Z e p p e l i n , 2 0 0 2 ) . P r e y s p e c i e s  34  r a n g e a c r o s s s e v e r a l t a x a s f r o m pelagic to b e n t h i c , a n d f r o m g r e g a r i o u s t o individualistic. Merrick  et  al. ( 1 9 9 7 ) c l a s s i f i e d t h e d i e t o f t h e S t e l l e r s e a lions in A l a s k a a s : g a d i d s (i.e. w a l l e y e p o l l o c k , Pacific c o d , a n d Pacific h a k e ) ; Pacific s a l m o n ; s m a l l s c h o o l i n g fish (i.e. c a p e l i n , Pacific h e r r i n g , e u l a c h o n , a n d Pacific s a n d l a n c e ) ; flatfish (i.e. a r r o w t o o t h f l o u n d e r a n d rock s o l e ) ; o t h e r d e m e r s a l fish (i.e. s c u l p i n s , r o c k f i s h , S t i c h a e i d a e , s k a t e s , s h a r k s , a n d l a m p r e y ) ; A t k a m a c k e r e l ; a n d c e p h a l o p o d s (i.e. s q u i d a n d o c t o p u s ) . T h e s e prey s p e c i e s u s e a w i d e v a r i e t y of a n t i p r e d a t o r  techniques, such as  s c h o o l i n g a n d c o n f u s i o n t e c h n i q u e s , cryptic b e h a v i o u r s , u s e o f n a t u r a l c o v e r s (i.e. k e l p b e d s a n d rocky o c e a n f l o o r ) , e t c . F o r a n active p r e d a t o r s u c h a s t h e s e a lion, p r e d a t o r y s u c c e s s d e p e n d s o n t h e ability to c o m e w i t h i n striking d i s t a n c e o f t h e prey a n d to m a i n t a i n this d i s t a n c e long e n o u g h to l a u n c h a strike ( n o r m a l l y a rapid neck e x t e n s i o n f o l l o w e d b y a b i t e , w h i c h o c c a s i o n a l l y i n v o l v e s s u c t i o n o f w a t e r — p e r s o n a l o b s e r v a t i o n s ) . T h e e x t e n t to w h i c h Steller s e a lions u s e collective f o r a g i n g t e c h n i q u e s is not c l e a r , but it a p p e a r s t h a t s e a lions typically c a p t u r e o n e prey a t a t i m e a n d h a v e to ingest it b e f o r e c a p t u r i n g t h e next o n e ( p e r s o n a l o b s e r v a t i o n s ) . T h u s t h e final b o u t o f all p r e d a t o r y strikes is a o n e - o n - o n e interaction b e t w e e n t h e s e a lion a n d its p r e y . It is d u r i n g this crucial  final  approach  towards  a  much  smaller  and  more  manoeuvrable  prey  item  that  manoeuvrability becomes an advantage (Howland, 1974).  T h e m o s t i m p o r t a n t m a r i n e p r e d a t o r s of t h e Steller s e a lion a r e killer w h a l e s a n d g r e a t w h i t e s h a r k s ( R i e d m a n , 1 9 9 0 ) . B e i n g significantly larger, t h e s e s p e c i a l i s e d s w i m m e r s c a n r e a c h h i g h e r s w i m m i n g s p e e d s t h a n s e a lions. T h e only c h a n c e of survival for t h e s e a lions c o n s i s t s o f o u t - m a n o e u v r i n g their p r e d a t o r s o r e s c a p i n g t o a terrestrial r e f u g e . A g a i n , a n u n s t a b l e b o d y d e s i g n a n d g o o d m a n o e u v r i n g capabilities a r e a definite a d v a n t a g e in t h e s e s i t u a t i o n s ( H o w l a n d , 1 9 7 4 ) .  From a  kinematic  perspective, the  morphological  features  of  the  otariids  present  undeniable  a d v a n t a g e s a n d c o n t r i b u t e t o their s u p e r i o r m a n o e u v r i n g c a p a b i l i t i e s c o m p a r e d t o o t h e r  marine  m a m m a l s (Fish et a l . , 2 0 0 3 ) . T h e r o u n d e d c r o s s - s e c t i o n o f t h e b o d y o f t h e s e a lion facilitates rolling, one of  the  preparatory  manoeuvres  executed before  performing  a  turn.  The  lack o f  lateral  c o m p r e s s i o n a n d d o r s a l f i n , w h i c h w o u l d resist rolling, a l l o w s t h e s e a lion to g e n e r a t e a rolling  35  m o m e n t w i t h o n l y a slight d e f l e c t i o n of o n e of t h e p e c t o r a l f l i p p e r s . C o n s i d e r i n g t h a t rolling a p p e a r s t o b e a n e c e s s a r y m a n o e u v r e p r e c e d i n g a t u r n , it is a d v a n t a g e o u s — if n o t n e c e s s a r y — t o r e d u c e its d u r a t i o n a n d its c o s t in o r d e r t o t u r n a s q u i c k l y a n d a s e c o n o m i c a l l y a s p o s s i b l e . H a v i n g a flexible b o d y a l l o w s t h e a n i m a l t o b e n d in t h e d i r e c t i o n of t h e t u r n a n d t h u s t o r e d u c e c r o s s - f l o w a n d additional pressure drag during the manoeuvre. Bending the body while entering t h e manoeuvre w i t h a n o n - z e r o s p e e d a l s o helps g e n e r a t i n g t h e rotational m o m e n t n e c e s s a r y t o t h e t u r n ( T u c k e r , 2000).  T h e l a r g e a n d v e r y m o b i l e p e c t o r a l flippers ( a v e r a g e o f 2 1 8 0 c m , w h i c h r e p r e s e n t s 5 6 % of t h e total 2  flipper s u r f a c e a r e a — T a b l e 2) of t h e Steller s e a lion a r e p o s i t i o n e d v e r y c l o s e t o t h e c e n t r e o f g r a v i t y a n d play a c r u c i a l role d u r i n g a t u r n . First, t h e y a c t a s i n d e p e n d e n t d e f l e c t o r s a n d p r o v o k e t h e b o d y roll; a n d s e c o n d , t h e y a c t a s hydrofoils g e n e r a t i n g a n i m p o r t a n t  lift f o r c e t o w a r d s t h e  inside o f t h e turn that c h a n g e s t h e trajectory o f the centre o f gravity. T h e y a r e also used t o produce t h r u s t d u r i n g a bilateral s t r o k e c y c l e t h a t m a k e s u s e o f b o t h lift a n d d r a g f o r c e s .  A s s h o w n b y F e l d k a m p ( 1 9 8 7 a ) f o r t h e C a l i f o r n i a s e a lion, t h e s t r o k e c y c l e o f t h e S t e l l e r s e a lion is m a d e up of a lift-based r e c o v e r y p h a s e a n d a p o w e r p h a s e b a s e d o n lift a t first a n d e n d i n g u p in a drag-based paddling movement. T h e recovery a n d power phases are performed during the turn. T h e r e c o v e r y p h a s e ( o r a b d u c t i o n ) t a k e s p l a c e d u r i n g t h e first half o f t h e t u r n a n d t h e p o w e r p h a s e ( o r a d d u c t i o n ) o c c u r s d u r i n g t h e s e c o n d half of t h e t u r n . T h e g r e a t e r t h e mobility o f t h e pectoral flippers, the higher t h e amplitude of t h e stroke cycle — a n d therefore, t h e greater t h e thrust.  T h e pelvic f l i p p e r s , w i t h a n a v e r a g e s u r f a c e of 1 7 0 0 c m ( 4 4 % o f t h e t o t a l f l i p p e r s u r f a c e a r e a — 2  T a b l e 2 ) , s e r v e t w o p u r p o s e s . First, t h e interdigital w e b of t h e pelvic flippers is fully e x t e n d e d d u r i n g t h e t u r n a n d resists a n o u t w a r d slip o f t h e pelvic a r e a . S e c o n d , a s in m a n y f l y i n g v e r t e b r a t e s , in w h i c h tails facilitate g e n e r a t i n g a e r o d y n a m i c t o r q u e s a n d s u b s t a n t i a l l y e n h a n c i n g t h e q u i c k n e s s of b o d y rotation ( D u d l e y , 2 0 0 2 ) , t h e y a r e u s e d a s a r u d d e r t o g e n e r a t e rotational m o m e n t s .  Fish et al. ( 2 0 0 3 ) m e a s u r e d m o r p h o l o g i c a l p a r a m e t e r s o n t h e f l i p p e r s o f t w o C a l i f o r n i a s e a lions, w h i c h p r e s e n t s o m e i n t e r e s t i n g d i f f e r e n c e s w i t h t h e flippers of Steller s e a lions. T h e t o t a l f l i p p e r a r e a  36  of t h e C a l i f o r n i a s e a lion u s e d in t h e i r s t u d y w a s a fraction o f t h e a v e r a g e Steller s e a lion flipper a r e a (total flipper a r e a : 0 . 2 2 7 m f o r t h e C a l i f o r n i a a n d 0 . 3 8 9 m f o r t h e Steller s e a l i o n s ) , e v e n t h o u g h t h e 2  a n i m a l s in b o t h  2  studies were  of c o m p a r a b l e size ( L = 1.89m  and mass=137.8kg  for the male  California a n d L = 1 . 8 7 m a n d m a s s = 1 3 7 . 7 k g o n a v e r a g e f o r t h e Steller s e a lions). T h i s d i s c r e p a n c y in t h e p r o j e c t e d a r e a of t h e f l i p p e r s m i g h t reflect a n e a r l y d e v e l o p m e n t o f t h e f l i p p e r s in t h e Steller s e a lion p r e c e d i n g t h e g r o w t h of t h e i r b o d y , w h i c h is ultimately  m u c h larger a n d heavier than the  California s e a lion. Steller s e a lions a r e t h e largest otariids w i t h t h e m a l e s r e a c h i n g u p t o 1,120kg and females to 350kg (Loughlin et a l . , 1 9 8 7 ; National Marine Fisheries Service, 1992; Winship et a l . , 2 0 0 1 ) . In c o m p a r i s o n , C a l i f o r n i a s e a lions g r o w u p t o a m a x i m u m of 3 9 0 k g f o r m a l e s a n d 1 1 0 k g f o r females (Riedman, 1990).  T h e d i f f e r e n c e in f l i p p e r a r e a o f t h e S t e l l e r a n d C a l i f o r n i a s e a lions a l s o a f f e c t s t h e kinetics o f  s w i m m i n g . A c c o r d i n g t o t h e lift e q u a t i o n (/_ =  ), t h e lift f o r c e (Z.) is directly  A CLU  2  P  to t h e s u r f a c e a r e a of t h e lift g e n e r a t i n g a p p e n d a g e (A )  proportional  such that the larger t h e surface area, the  P  h i g h e r t h e lift v a l u e ( H o e r n e r a n d B o r s t , 1 9 7 5 ) . F r o m a k i n e m a t i c p e r s p e c t i v e , h i g h e r lift f o r c e s p r o d u c e d b y t h e flippers t r a n s l a t e into a m o r e s u d d e n c h a n g e o f t r a j e c t o r y  a n d a quicker  rotation. Furthermore, the amount of water accelerated during the drag-based paddling  body  movement  o f t h e p e c t o r a l flippers is r e l a t e d t o t h e s u r f a c e a r e a of c o n t a c t b e t w e e n t h e l i m b a n d t h e w a t e r . In this w a y , l a r g e flippers m o v e d s l o w l y p r o d u c e t h r u s t m o r e efficiently t h a n s m a l l flippers rapidly  (English,  1976).  Based  only  on  flipper  size,  Steller  s e a lions  would  moved  appear  more  m a n o e u v r a b l e a n d m o r e efficient s w i m m e r s t h a n t h e C a l i f o r n i a s e a lions. H o w e v e r , this a p p a r e n t a d v a n t a g e is p r o b a b l y n e g a t e d by t h e fact t h a t t h e larger Steller s e a lions suffer f r o m a s u b s t a n t i a l l y higher body drag.  Theoretically,  the  relatively  small  Steller  s e a lions  that  I  studied  should  have  been  more  m a n o e u v r a b l e t h a n t h e C a l i f o r n i a s e a lions t h a t Fish e t a l . ( 2 0 0 3 ) s t u d i e d . H o w e v e r , m y results d o not s u p p o r t this h y p o t h e s i s ( s e e F i g . 1 3 ) , p e r h a p s b e c a u s e o t h e r p a r a m e t e r s s u c h a s m o t i v a t i o n levels p l a y e d a role in t h e individual s w i m m i n g  p e r f o r m a n c e of e a c h a n i m a l . A n o t h e r  possible  37  e x p l a n a t i o n is t h a t t h e a s p e c t ratio of t h e pectoral f l i p p e r s of t h e C a l i f o r n i a s e a lions w a s g r e a t e r t h a n t h a t o f t h e Steller s e a lions, w h i c h c o u l d h a v e r e s u l t e d in t h e f l i p p e r s o f t h e C a l i f o r n i a s e a lions g e n e r a t i n g a g r e a t e r lift f o r c e ( H o e r n e r a n d B o r s t , 1 9 7 5 ) . T h u s t h e d e g r e e o f  manoeuvrability  b e t w e e n California a n d Steller s e a lions m y h a v e b e e n c o m p e n s a t e d b y t h e d i f f e r e n c e in flipper shape between the two species.  In t h e c a s e of large e n d o t h e r m s inhabiting t h e c o l d w a t e r s o f t h e N o r t h Pacific O c e a n a n d t h e Bering S e a , g r o w i n g l a r g e s w i m m i n g a p p e n d a g e s will i n d u c e h i g h t h e r m o - e n e r g e t i c c o s t s . I n l a r g e a d u l t a n i m a l s t h a t e x p e r i e n c e c o n s i d e r a b l e inertial f o r c e s a n d r e q u i r e  large c o n t r o l  surface areas to  m a i n t a i n a c e r t a i n d e g r e e o f m a n o e u v r a b i l i t y , t h e b i o m e c h a n i c a l a d v a n t a g e s d r a w n f r o m t h e s e large flippers c a n b e p r e s u m e d t o c o m p e n s a t e f o r t h e t h e r m o r e g u l a t i o n c o s t s . B u t t h e fact t h a t y o u n g e r a n d s m a l l e r a n i m a l s — w h i c h e x p e r i e n c e less inertia — g r o w large flippers a t a n e a r l y a g e s u g g e s t s t h a t y o u n g a n i m a l s a l s o d r a w k i n e m a t i c a d v a n t a g e s f r o m e n l a r g e d f l i p p e r s , s u c h a s h i g h e r lift a n d thrust forces.  Kinematic analysis S o m e aspects of the turning technique appear to be closely related, e v e n though the  different  e l e m e n t s of t h e t u r n i n g s e q u e n c e s h o w a certain d e g r e e of t e m p o r a l variability. T a b l e 3 illustrates t h a t t h e first t h r e e m o v e m e n t s o f t h e s e q u e n c e ( n o t a b l y t h e h e a d d i s p l a c e m e n t i n s i d e t h e t u r n , t h e a b d u c t i o n o f t h e p e c t o r a l flippers a n d t h e start o f t h e rolling m o v e m e n t o f t h e b o d y ) d o not follow a definite s e q u e n c e a n d a r e i n t e r c h a n g e a b l e . I n d e e d , t h e position o f t h e h e a d is c l o s e l y l i n k e d t o t h e a n i m a l ' s field o f v i e w , w h e r e b y  d i s p l a c i n g t h e h e a d inside t h e t u r n m e a n s c o m m i t t i n g  to the  m a n o e u v r e . I n o t h e r w o r d s , t h e a n i m a l m o v e s its h e a d inside o f t h e t u r n a n d s t o p s l o o k i n g a h e a d , t h e r e b y c r e a t i n g a rotational m o m e n t ( y a w ) t h a t initiates t h e rest of t h e m a n o e u v r e . T h e t u r n is not irreversible a t this point b u t d e m a n d s a d j u s t m e n t s t o c o n t r o l y a w t o r e v e r s e t h e m o v e m e n t , w h i c h is t i m e c o n s u m i n g a n d i n d u c e s a h i g h e r v a l u e of d r a g ( s e e T u c k e r , 2 0 0 0 ) . M o r e o v e r , c o s t s i n c r e a s e w i t h i n c r e a s e d s p e e d , g i v e n t h a t d r a g scales w i t h t h e s q u a r e o f s p e e d .  38  In a situation w h e r e t h e s e a lion is uncertain a b o u t t h e recall s i g n a l , it w o u l d be a d v a n t a g e o u s to d e l a y t h e h e a d m o v e m e n t slightly b e f o r e c o m m i t t i n g t o t h e t u r n . It is w o r t h m e n t i o n i n g t h a t I n e v e r o b s e r v e d t h e rolling m o v e m e n t w i t h m y s t u d y a n i m a l s b e f o r e t h e start o f t h e a b d u c t i o n o f t h e pectoral f l i p p e r s . T h i s s u p p o r t s t h e h y p o t h e s i s t h a t rolling is c o n t r o l l e d by a n a s y m m e t r i c a l deflection of t h e p e c t o r a l flippers d u r i n g t h e e a r l y s t a g e o f t h e a b d u c t i o n .  Directly f o l l o w i n g this initial p h a s e ( h e a d m o v e m e n t , b o d y roll, a n d start o f t h e pectoral flipper a b d u c t i o n ) , t h e a n i m a l p r o c e e d s t o a r c h its b o d y d o r s a l l y , r o t a t e s its p e l v i c f l i p p e r s o u t w a r d s a n d e x t e n d s t h e interdigital w e b of t h e pelvic flippers. T h e s e e v e n t s o f t e n h a p p e n s i m u l t a n e o u s l y , but w h e n t h e y d o not, t h e b o d y flexion p r e c e d e s m o s t o f t h e t i m e ( T a b l e 3 ) .  T h e pelvic flippers s e r v e t w o p u r p o s e s d u r i n g a m a n o e u v r e : a) t h e y c o n t r o l t h e m o v e m e n t o f t h e posterior part o f t h e b o d y a n d p r e v e n t a n o u t w a r d slip a n d b) t h e y g e n e r a t e rotational W h e n the animal's trajectory  moment.  is rectilinear, t h e p e l v i c f l i p p e r s a r e in a p o s i t i o n t h a t m i n i m i s e s  e x p o s e d s u r f a c e a n d t h e r e f o r e , friction d r a g . R o t a t i n g t h e pelvic f l i p p e r s a n d e x p o s i n g a m a x i m u m s u r f a c e b e f o r e t h e b o d y starts m a n o e u v r i n g is t h u s d e t r i m e n t a l kinetically b e c a u s e o f t h e u n d e s i r e d f o r c e s t h u s c r e a t e d . T h e o n s e t of t h e pelvic f l i p p e r s ' m o v e m e n t is s i m u l t a n e o u s t o t h e start of t h e d o r s a l a r c h . A t t h a t point, t h e pelvic c o n t r o l s u r f a c e s start t o b e at a n a n g l e w i t h t h e rest o f t h e b o d y a n d s e r v e a s a r u d d e r . F u r t h e r m o r e , t h e b o d y itself t a k e s part in g e n e r a t i n g rotational  moment  w h e n it a r c h e s into t h e t u r n (as s u g g e s t e d by T u c k e r , 2 0 0 0 ) . In s h o r t , t h e s e c o n d p h a s e o f t h e t u r n i n g s e q u e n c e s e e s t h e g r o w t h o f t h e c e n t r i p e t a l f o r c e , w h i c h results in a c h a n g e o f s w i m m i n g trajectory.  D u r i n g P h a s e 3 , t h e rolling m o v e m e n t a n d t h e a b d u c t i o n o f t h e p e c t o r a l f l i p p e r s s t o p a t m a x i m u m v a l u e . B o t h e v e n t s a r e closely related a n d often  their  happen simultaneously because the  p e c t o r a l flippers c r e a t e a large s u r f a c e a r e a t h a t resists t h e  rolling  movement once they  are  s t a t i o n a r y a n d m a x i m a l l y a b d u c t e d . W h e n b o t h e v e n t s a r e not s i m u l t a n e o u s t h e flipper a b d u c t i o n a l w a y s e n d s b e f o r e t h e rolling m o v e m e n t ( T a b l e 3 ) . T h i s c o n f i r m s t h e f a c t t h a t t h e a b d u c t i o n o f t h e pectoral flippers is r e s p o n s i b l e for t h e c r e a t i o n of t h e rolling m o v e m e n t .  39  Roll a r i s e s w h e n t h e t w o c o n t r o l s u r f a c e a r e a g e n e r a t e different a m o u n t s o f lift f o r c e ( H o e r n e r a n d B o r s t , 1 9 7 5 ) . I n t h e c a s e o f a n aircraft, t h e a i l e r o n s a r e u s e d t o v a r y t h e a m o u n t of lift g e n e r a t e d b y e a c h w i n g . I n t h e a b s e n c e of flipper a i l e r o n s , s e a lions rely o n o t h e r m e c h a n i s m s t o c r e a t e this d i f f e r e n c e in lift f o r c e . O n e m e c h a n i s m is t o v a r y t h e a n g l e o f a t t a c k o f e a c h f l i p p e r , w h i c h affects lift f o r c e . T h e s e c o n d m e c h a n i s m a c t s n o t o n t h e f o r c e directly, b u t o n t h e d i s t a n c e b e t w e e n t h e flipper a n d t h e m i d l i n e of t h e b o d y . T h e g r e a t e r this d i s t a n c e , t h e h i g h e r t h e m o m e n t of f o r c e . T h e r e f o r e , rolling m o m e n t is c r e a t e d b y a b d u c t i n g t h e o u t e r flipper (i.e. t h e left f l i p p e r in a right t u r n ) q u i c k e r t h a n t h e inner flipper. T h i s e x p l a i n s w h y rolling c o n t i n u e s w h i l e t h e flippers a r e a p p a r e n t l y fully a b d u c t e d ( i . e . t h e inner f l i p p e r t h a t is a w a y f r o m t h e c a m e r a — F i g . 5 — w a s p r e s u m a b l y still in m o t i o n ) . H o w e v e r , t h e s e h y p o t h e s e s c a n n o t be v e r i f i e d w i t h t h e p r e s e n t r e c o r d i n g s b e c a u s e t h e a n g l e o f v i e w o f t h e c a m e r a a n d t h e resolution o f t h e i m a g e s d i d n o t a l l o w d e t a i l e d a n a l y s i s o f t h e motion of the pectoral flippers.  D u r i n g P h a s e 4 , t h e b o d y o f t h e a n i m a l is m a x i m a l l y a r c h e d a n d t h e a d d u c t i o n ( m o v e m e n t t o w a r d s t h e m i d l i n e of t h e b o d y ) o f t h e pectoral flippers s t a r t s . W h i l e P h a s e 3 c o r r e s p o n d e d t o a b o u t o f m i n i m u m s p e e d , this p h a s e m a r k s t h e b e g i n n i n g o f t h e p o w e r s t r o k e a n d t h e a c c e l e r a t i o n o u t o f t h e m a n o e u v r e . T h e a d d u c t i o n o f t h e pectoral flipper is a k i n t o t h e d e s c r i p t i o n o f F e l d k a m p ( 1 9 8 7 a ) , a n d starts w i t h a d o r s o - v e n t r a l p o w e r s t r o k e (or p o w e r p h a s e in F e l d k a m p ' s t e r m i n o l o g y ) . A s n o t e d b y Feldkamp, such a m o v e m e n t creates a force oriented forwardly a n d dorsally. T h e timing of the onset of t h e p e c t o r a l a d d u c t i o n w i t h , o r slightly b e f o r e , t h e m a x i m u m c u r v a t u r e o f t h e b o d y , a l l o w s t h e a n i m a l t o m a k e o p t i m a l u s e of t h e d o r s a l c o m p o n e n t of t h e f o r c e . A t this point in t h e m a n o e u v r e , t h e b o d y is a r c h e d in a U - s h a p e a n d t h e c e n t r e of m a s s is in t h e m i d d l e of t h e c u r v e d part of t h e trajectory. T h e t i m e l y o n s e t o f t h e dorsally o r i e n t e d f o r c e t h e r e f o r e p r o v i d e s a useful c e n t r i p e t a l c o m p o n e n t a n d a f o r w a r d c o m p o n e n t . P e r f o r m e d e a r l i e r in t h e m a n o e u v r e , t h e p o w e r s t r o k e w o u l d leave t h e a n i m a l w i t h o u t c o n t r o l o v e r t h e later s t a g e s of t h e t u r n ( b e c a u s e t h e c o n t r o l s u r f a c e s w o u l d t h e n b e in a v e n t r a l p o s i t i o n ) . S h o u l d t h e s e a lion p r o d u c e a late s t r o k e , it w o u l d c a u s e t h e a n i m a l t o l o o s e s u b s t a n t i a l a m o u n t o f s p e e d o v e r t h e e a r l i e r s t a g e s of t h e t u r n i n g m a n o e u v r e d u r i n g w h i c h n o t h r u s t is p r o d u c e d .  40  P h a s e 5 is t h e e n d of t h e m a n o e u v r e . T h e b o d y r e g a i n s a s t r a i g h t o r i e n t a t i o n , a n d t h e a d d u c t i o n of t h e p e c t o r a l flippers r e a c h e s a n e n d . T h e e n d o f t h e b o d y flexion o f t e n c o m e s first a s t h e a n i m a l s l o w l y t e r m i n a t e s t h e p a d d l e p h a s e . O n t h e s e o c c a s i o n s , t h e e n d o f t h e p a d d l e p h a s e c o n s i s t s of a p a s s i v e a d d u c t i o n d u r i n g w h i c h t h e flippers a r e b r o u g h t up t o w a r d s t h e v e n t r a l f l a n k s o f t h e a n i m a l . N o t h r u s t is p r o d u c e d d u r i n g t h e p a d d l e p h a s e .  D u r i n g P h a s e 6, t h e pelvic flippers exit t h e t u r n a n d r e g a i n a g l i d i n g p o s i t i o n . T h e interdigital w e b r e m a i n s e x t e n d e d a s l o n g a s t h e pelvic flippers f o l l o w t h e c u r v e d t r a j e c t o r y . A s s o o n a s t h e a n g l e b e t w e e n t h e m i d l i n e o f t h e b o d y a n d t h e pelvic flippers returns t o z e r o , t h e y b e g i n to rotate a n d t h e flipper s u r f a c e a r e a d i m i n i s h e s .  T h e t u r n i n g s e q u e n c e v a r i e d b e t w e e n t h e t h r e e a n i m a l s I s t u d i e d . First, all t h r e e d i s p l a y e d a s t r o n g directional p r e f e r e n c e . S L 1 a n d S L 3 a l w a y s p e r f o r m e d right t u r n s w h e r e a s S L 2 p e r f o r m e d left t u r n s . In t h e c a s e of S L 3 , t h e s i d e p r e f e r e n c e w a s potentially a f f e c t e d by h e r i m p a i r e d e y e s i g h t o n t h e left e y e . S h e m a y h a v e c h o s e n t h e direction of t h e t u r n a c c o r d i n g t o h e r field o f v i e w , w h i c h w a s m o s t l y o n her right s i d e . F o r t h e o t h e r t w o a n i m a l s , it is difficult to d e t e r m i n e w h i c h o n e o f t h e m u s c u l a r , structural, or behavioural preferences mostly caused these directional preferences. Table 3 also s h o w s t h a t S L 3 t e n d e d t o start rolling o n l y after h e r h e a d a n d p e c t o r a l f l i p p e r s w e r e in m o t i o n , w h e r e a s S L 1 a n d S L 2 p e r f o r m e d all t h r e e b e h a v i o u r s i n t e r c h a n g e a b l y . H e r e a g a i n , d e l a y i n g t h e roll f o r S L 3 m a y h a v e b e e n a b e h a v i o u r a l a d a p t a t i o n to h e r i m p a i r e d left e y e . W h i l e t h e a n i m a l s p e r f o r m e d t h e i r m a n o e u v r e s t h e y t e n d e d to k e e p v i s u a l c o n t a c t w i t h t h e t r a i n e r s , a n d t h u s rolling t h e right s i d e d o w n w a r d s in a right t u r n w o u l d h a v e r e d u c e d S L 3 ' s field o f v i e w o f t h e s u r f a c e . F o r t h e s a m e r e a s o n , all t h r e e a n i m a l s rolled their h e a d s less t h a n t h e rest o f t h e i r b o d y d u r i n g t h e t u r n . T h e d e g r e e of b o d y roll, w h i c h w a s linked t o t h e 3 D s w i m m i n g p a t h d u r i n g t h e t u r n , a l s o v a r i e d b e t w e e n m a n o e u v r e s . If it w a s s u p e r i o r to 9 0 d e g r e e s , t h e a n i m a l t e n d e d t o d i v e , a n d c o n v e r s e l y if it w a s less t h a n 9 0 d e g r e e s , t h e a n i m a l c a m e c l o s e r to t h e s u r f a c e .  O n t o p o f t h e v a r i a t i o n s o f t u r n i n g t e c h n i q u e a n d s e q u e n c e o f a c t i o n s , d i f f e r e n c e s in t h e w a y certain m o v e m e n t s w e r e p e r f o r m e d w e r e o b s e r v e d . For i n s t a n c e , d o r s a l c u r v a t u r e v a r i e d w i t h  turning  41  r a d i u s , i.e. t h e larger t h e t u r n i n g radius, t h e s t r a i g h t e r t h e b o d y ( F i g . 7 ) . I n w i d e t u r n s , w h i c h i n v o l v e d a l o w rotational m o m e n t , r e d u c i n g t h e d o r s a l flexion a n d t h u s m a i n t a i n i n g a s t r e a m l i n e d b o d y s h a p e w a s a d v a n t a g e o u s b e c a u s e it limited t h e d e c e l e r a t i o n d u e t o f o r m d r a g . In tight t u r n s h o w e v e r , t h e f a s t rotation o f a n o n - f l e x i n g b o d y w o u l d result in t h e c r e a t i o n o f a n i m p o r t a n t lateral p r e s s u r e d r a g o v e r t h e e n t i r e b o d y l e n g t h . In t h e s e s i t u a t i o n s , t h e c u r v e d b o d y limited t h e lateral drag.  A b d u c t i o n o f t h e p e c t o r a l flippers w a s a n o t h e r v a r i a b l e t h a t d i f f e r e d b e t w e e n a n i m a l s . T h e g e n e r a l s t r o k e t e c h n i q u e c a n b e d i v i d e d in t h r e e m a j o r s e c t i o n s a s p r e s e n t e d b y F e l d k a m p ( 1 9 8 7 a ) . D u r i n g t h e r e c o v e r y p h a s e , t h e l e a d i n g e d g e o f t h e pectoral f l i p p e r is r o t a t e d o u t w a r d s a n d b r o u g h t f o r w a r d a n d dorsally t o v a r y i n g d e g r e e s of s w e e p ( i . e . a n g l e b e t w e e n t h e m i d l i n e of t h e flipper a n d t h e midline o f t h e b o d y ) a n d d i h e d r a l (i.e. a n g l e b e t w e e n t h e s u r f a c e t h e f l i p p e r a n d t h e h o r i z o n t a l p l a n e w h i c h c o n t a i n s t h e m i d l i n e o f t h e b o d y ) . It f o l l o w s t h e p o w e r p h a s e d u r i n g w h i c h t h e flippers a r e rotated i n w a r d s , a n d b r o u g h t v e n t r a l l y a n d b a c k w a r d . T h e s t r o k e e n d s w i t h t h e p a d d l e p h a s e d u r i n g w h i c h t h e f l i p p e r s c o n t i n u e t o rotate i n w a r d s a n d m o v e b a c k w a r d s a n d u p , t o r e s t o n t h e v e n t r a l f l a n k s o f t h e a n i m a l . A s m e n t i o n e d a b o v e , t h e s w e e p a n d d i h e d r a l o f t h e p e c t o r a l flippers v a r y in different t u r n s . Particularly in v e r y s l o w t u r n s , t h e p e c t o r a l flippers a r e not fully a b d u c t e d , i.e. t h e s w e e p d o e s not a p p r o a c h 9 0 d e g r e e s ( p e r p e n d i c u l a r t o t h e m i d l i n e o f t h e b o d y ) a n d t h e d i h e d r a l is m u c h less p r o n o u n c e d t h a n d u r i n g f a s t e r t u r n s ( F i g . 1 2 ) .  A c c o r d i n g t o t h e a e r o d y n a m i c t h e o r y , lift a n d d r a g d e c r e a s e w i t h t h e d i s t a n c e b e t w e e n t h e liftg e n e r a t i n g a p p e n d a g e s a n d t h e b o d y ( H o e r n e r a n d Borst, 1 9 7 5 ) . F o r s e a lions p e r f o r m i n g a s l o w t u r n , it is t h e r e f o r e a d v a n t a g e o u s t o k e e p t h e p e c t o r a l flipper c l o s e f r o m t h e b o d y b e c a u s e a ) it m i n i m i s e s t h e d r a g f o r c e a n d d e c e l e r a t i o n rate a n d b) t h e s y s t e m d o e s n o t r e q u i r e a high lift f o r c e to m a k e its t r a j e c t o r y c h a n g e . Finally, a n i m p o r t a n t positive d i h e d r a l is s y n o n y m o u s t o a s t r o k e of high a m p l i t u d e , w h i c h h a s b e e n positively c o r r e l a t e d w i t h s w i m m i n g s p e e d ( F e l d k a m p , 1 9 8 7 a ) a n d t h e r e f o r e is u n n e c e s s a r y in a s l o w m a n o e u v r e .  42  T h e t u r n i n g t e c h n i q u e o f t h e C a l i f o r n i a s e a lions a n d S t e l l e r s e a lions is strikingly s i m i l a r (Fish et a l . , 2 0 0 3 ) e v e n t h o u g h t h e C a l i f o r n i a s e a lion t e n d s to p e r f o r m t h e m a n o e u v r e relatively f a s t e r ( F i g . 13) a n d h a v e slightly different m o r p h o l o g i c a l c h a r a c t e r i s t i c s ( s e e a l s o E n g l i s h , 1 9 7 6 ; F e l d k a m p , 1 9 8 7 a ) . Fish e t a l . ( 2 0 0 3 ) n o t e d t h a t t h e a t t i t u d e o f t h e f l i p p e r s in t h e C a l i f o r n i a s e a lion is h i g h l y v a r i a b l e a n d t h a t t h e b o d y o f t h e a n i m a l is v e r y flexible d o r s a l l y . It is this c o m b i n a t i o n o f highly m o b i l e control  surfaces and  b o d y flexibility  that  provides  both  species with an  impressive array  of  m a n o e u v r i n g capabilities w i t h o u t h a v i n g to c h a n g e t h e basic t u r n i n g t e c h n i q u e itself. For e x a m p l e , t h e inclination o f t h e t u r n i n g p l a n e is d e t e r m i n e d by t h e rolling d e g r e e ; t h e t i g h t n e s s of t h e t u r n v a r i e s w i t h t h e b o d y f l e x i o n ; a n d t h e a m p l i t u d e o f t h e s t r o k e i n f l u e n c e s s p e e d . T h i s is w h y t h e six p h a s e s of t h e g e n e r a l t u r n i n g t e c h n i q u e a r e q u i t e c o n s i s t e n t e v e n t h o u g h m i n o r v a r i a t i o n s in t h e turning sequence are observed.  S e a lions a r e c a p a b l e o f f i n e - t u n i n g  parts of t h e t u r n i n g  s e q u e n c e a n d a d a p t i n g it to  various  s i t u a t i o n s , w h i c h g i v e s t h e m a n o e u v r i n g t e c h n i q u e g r e a t e r versatility (i.e. rolling w i t h o u t d e v i a t i n g f r o m a rectilinear s w i m m i n g path b e f o r e starting t h e t u r n i n g  m a n o e u v r e ; controlling the  rolling  d e g r e e o f t h e h e a d t o m a i n t a i n v i s u a l c o n t a c t w i t h a particular o b j e c t ; m o d i f y i n g t h e rolling d e g r e e o f t h e b o d y to i n f l u e n c e t h e a n i m a l ' s position in t h e w a t e r c o l u m n a t t h e e n d o f t h e m a n o e u v r e ; varying the pectoral flipper stroke to control thrust production). Using this o n e general turning t e c h n i q u e , t h e a n i m a l c a n t h e r e f o r e p r o d u c e a n a l m o s t infinite n u m b e r o f u n d e r w a t e r m a n o e u v r e s . It is p r o b a b l y f o r this r e a s o n t h a t t h e t u r n i n g t e c h n i q u e o b s e r v e d in o t h e r o t a r i i d s , s u c h a s t h e California s e a l i o n , is virtually identical to t h e o n e o b s e r v e d h e r e .  In c o n t r a s t , o t h e r m a r i n e m a m m a l s s u c h a s d o l p h i n s a n d w h a l e s d o n o t h a v e this m a n o e u v r i n g c a p a b i l i t y a n d h a v e t o rely o n a r a n g e o f t u r n i n g t e c h n i q u e s w h e t h e r t h e y w a n t t o m i n i m i s e t u r n i n g r a d i u s , o r d e c e l e r a t i o n , o r m a x i m i s e t u r n i n g rate. T h e b o t t l e n o s e d o l p h i n f o r e x a m p l e relies o n a " p i n w h e e l " t e c h n i q u e to m i n i m i s e t h e t u r n i n g radius o f its m o u t h a r e a a n d m a x i m i s e its t u r n i n g rate. M a r e s h e t a l . ( 2 0 0 4 ) d e s c r i b e d t h e m a n o e u v r e itself in t h e s e t e r m s : " D u r i n g t h e p i n w h e e l , t h e a n i m a l a p p e a r e d t o k e e p its r o s t r u m at a fixed point, a n d rapidly rotate its b o d y a r o u n d t h a t p o i n t . "  43  S u c h a m a n o e u v r e e s s e n t i a l l y t r a n s f o r m s all t h e t r a n s l a t i o n s p e e d o f t h e s y s t e m into  rotational  s p e e d . But t h e d o l p h i n t h u s offering its e n t i r e s i d e to a n i m p o r t a n t c r o s s - f l o w p r o b a b l y p a y s a s u b s t a n t i a l price a n d e n d u r e s a significant d e c e l e r a t i o n d u e t o t h e c r e a t i o n of p r e s s u r e d r a g a r o u n d its b o d y . M o r e o v e r , a s t h r u s t c a n n o t b e p r o d u c e d d u r i n g t h e p i n w h e e l itself, t h e a n i m a l h a s t o " w a i t " until t h e e n d of t h e m a n o e u v r e b e f o r e it c a n r e - a c c e l e r a t e . In t h e c a s e of t h e s e a lions, this d e l a y is m i n i m i s e d a s t h e y rely o n their large a n d m o b i l e pectoral flippers t o s t a r t a c c e l e r a t i n g half w a y through the turn.  • Trajectory of the nose • Trajectory o f t h e s h o u l d e r  •*  •  Plexiglas sheet  •  *•.  | \ • *  Origin  Fig. 10: T r a j e c t o r y o f t h e n o s e a n d s h o u l d e r o f a s e a lion p e r f o r m i n g a 180 d e g r e e s t u r n a s f i l m e d f r o m a b o v e t h r o u g h a P l e x i g l a s s h e e t . 1. T h e n o s e o f t h e a n i m a l is d i s p l a c e d inside t h e t u r n a n d g e n e r a t e s a t r a j e c t o r y t h a t h a s a n initial h i g h c u r v a t u r e . 2. A s t h e a n i m a l p e r f o r m s a s t r o k e o u t o f t h e m a n o e u v r e a n d s t r a i g h t e n s its b o d y , t h e d o r s a l c o m p o n e n t o f t h e t h r u s t f o r c e h a s t o b e c o r r e c t e d by a m o v e m e n t o f t h e h e a d a n d n e c k o f t h e a n i m a l ( r e p r e s e n t e d h e r e b y the trajectory of the nose).  Fig. l l : C o m p a r i s o n o f t h e s p e e d profiles o f t h e s h o u l d e r , c e n t r e o f gravity, a n d hips m a r k e r s o f a Steller s e a lion p e r f o r m i n g a 180 d e g r e e s t u r n w i t h t h e p r e d i c t i o n s o f a t h e o r e t i c a l m o d e l o f t h e s p e e d v a r i a t i o n o f a S t e l l e r s e a lion t h r o u g h a n u n p o w e r e d t u r n ( B l a k e a n d C h a n , in r e v i e w ) . T h e black lines r e p r e s e n t t h e m o d e l predictions. E a c h o n e o f t h e t h r e e lines is b a s e d o n a different r e f e r e n c e d a r e a , i.e. total w e t t e d s u r f a c e a r e a , frontal s u r f a c e a r e a , o r v o l u m e . F o r a d i s c u s s i o n o n t h e d i f f e r e n c e b e t w e e n r e f e r e n c e areas, see Alexander (1990). 2 7 3  3.9 — Shoulder  — Centre Of arsvity - - Wetted surface area 3-5  Frontal surface area  • Volume '  2 3  1.6  2.0  Time [s]  Fig. 12: C o m p a r i s o n o f t h e s p e e d profiles o f t h e s h o u l d e r , c e n t r e o f gravity, a n d h i p s m a r k e r s o f a Steller s e a lion p e r f o r m i n g a fast a n d a s l o w 180 d e g r e e s t u r n . N o t e t h e d i f f e r e n c e in d e c e l e r a t i o n a n d a c c e l e r a t i o n a s well a s t h e a v e r a g e s p e e d in b o t h t u r n s . T h e black lines o n t h e g r a p h s r e p r e s e n t t h e p r e d i c t i o n s o f t h e theoretical m o d e l o f a n u n p o w e r e d t u r n ( B l a k e a n d C h a n , in r e v i e w ) . T h e a n i m a l ' s m i d l i n e a n d flipper position is indicated in t h e t o p - d o w n v i e w o n t h e l e f t - h a n d s i d e . In t u r n A . t h e profile o f t h e pectoral flipper in t h e m i d d l e o f t h e t u r n is v e r y s h o r t ( i n d i c a t e d by t h e circle a n d t h e a r r o w ) , w h i c h m e a n s t h a t t h e s w e e p a n g l e o f t h e pectoral flippers is c l o s e to 9 0 d e g r e e s . T h i s is n o t t h e c a s e in t u r n B. w h e r e t h e profile o f t h e pectoral flipper is l o n g e r a n d d o e s not m o v e far f r o m t h e b o d y ' s m i d l i n e ( i n d i c a t e d by t h e circle a n d t h e a r r o w ) .  47  2  5  u o  1.5  2  0  0.1  0.2  0.3  0.4  Radius (L)  Fig. 13: Relative turning radius and average turning speed of three Steller sea lions in comparison to California sea lions (shaded area). Both turning radius and speed are expressed relative to the body length (L). The California sea lion data is taken from Fish et al. (2003).  48  Kinetic  analysis  T h e s p e e d profiles of m o s t t u r n s h a d a typical V - s h a p e , p r e c e d e d a n d f o l l o w e d by b o u t s of c o n s t a n t (or slightly d e c r e a s i n g ) s p e e d ( F i g . 8 ) , w h i c h c o r r e s p o n d e d to t h e g l i d e s a t t h e b e g i n n i n g a n d a t t h e e n d of t h e t u r n s . A s t h e a n i m a l s t a r t e d orienting its b o d y inside o f t h e t u r n a n d a b d u c t e d its p e c t o r a l flippers, t h e d e c e l e r a t i o n b e c a m e m o r e p r o n o u n c e d ( F i g . 8 ) . T h i s d e c e l e r a t i o n c o n t r a s t s w i t h t h e analysis o f t h e f o r e f l i p p e r p r o p u l s i o n o f t h e C a l i f o r n i a s e a lion ( F e l d k a m p , 1 9 8 7 a ) , w h i c h s h o w e d t h a t a b d u c t i o n of t h e p e c t o r a l flippers (i.e. t h e r e c o v e r y p h a s e ) c r e a t e s t h r u s t .  T h e discrepancy between m y findings a n d those of Feldkamp (1987a) might be because Steller sea lions a n d C a l i f o r n i a s e a lions u s e a different s t r o k e t e c h n i q u e . But t h e d i f f e r e n c e is m o r e likely b e c a u s e F e l d k a m p s t u d i e d s e a lions s w i m m i n g linearly a g a i n s t a n i n c o m i n g c u r r e n t . T h e r e a r e o b v i o u s a d v a n t a g e s to  producing thrust during as much of the stroke cycle as possible w h e n  s w i m m i n g in a straight line. H o w e v e r , c r e a t i n g a f o r w a r d f o r c e w h i l e p r e p a r i n g a n d a d j u s t i n g f o r a manoeuvre can be destabilising.  Pectoral flippers s e r v e a d u a l p u r p o s e of c r e a t i n g c e n t r i p e t a l f o r c e a n d t h r u s t d u r i n g t h e t u r n . T o p e r f o r m a t u r n , t h e a n i m a l a b d u c t s a n d positions its c o n t r o l s u r f a c e s in a m a n n e r t h a t will g e n e r a t e as m u c h c e n t r i p e t a l f o r c e a s p o s s i b l e . T h i s r e q u i r e m e n t is q u i t e different f r o m t r y i n g to g e n e r a t e a s much forward  t h r u s t a s p o s s i b l e (i.e. t h e flippers h a v e a different  a n g l e of a t t a c k d u r i n g  the  abduction, the degree of dihedral varies, etc.). Therefore, I suggest that otariids fine-tune the stroke t e c h n i q u e t o preferentially p r o d u c e t h r u s t d u r i n g d e f i n e d parts o f t h e s t r o k e c y c l e , i.e. b y c h a n g i n g t h e a n g l e o f a t t a c k of t h e p e c t o r a l f l i p p e r s , o r t h e d i h e d r a l a n d a m p l i t u d e o f t h e s t r o k e , o r t h e s w e e p of the pectoral flippers, etc.  T h e a d d u c t i o n o f t h e p e c t o r a l flippers o f t h e S t e l l e r s e a lion is c o m p o s e d o f t h e t w o  phases  d e s c r i b e d b y F e l d k a m p ( 1 9 8 7 a ) : t h e p o w e r p h a s e f o l l o w e d b y t h e p a d d l e p h a s e . In m y s t u d y , I o b s e r v e d t h e latter w h e n a p a s s i v e glide f o l l o w e d t h e s t r o k e but n o t e d t h a t it w a s o m i t t e d w h e n t h e a n i m a l p e r f o r m e d t w o s u c c e s s i v e s t r o k e s . In C a l i f o r n i a s e a lions s w i m m i n g rectilinearly, m o s t of t h e propulsive force comes from  the  p a d d l e p h a s e ( F e l d k a m p , 1 9 8 7 a ) . In  comparison, my  results  49  s h o w e d t h a t m o s t of t h e t h r u s t p r o d u c t i o n o c c u r s d u r i n g t h e p o w e r p h a s e . A c c e l e r a t i o n s t o p s at t h e e n d of t h e p o w e r p h a s e , w h i c h indicates t h a t t h e p a d d l e p h a s e p r o d u c e s little t h r u s t .  T h e fact t h a t  t h e a n i m a l b y - p a s s e s t h e p a d d l e p h a s e a l t o g e t h e r d u r i n g a d o u b l e s t r o k e f u r t h e r s u p p o r t s this finding. A t t h e o n s e t o f t h e p o w e r p h a s e , t h e a n i m a l is in t h e m i d d l e of t h e t u r n a n d its b o d y is b e n t d o r s a l l y in a U - s h a p e . A t this point, t h e d o r s o - v e n t r a l m o v e m e n t o f t h e p e c t o r a l f l i p p e r s g e n e r a t e s a dorsally o r i e n t e d f o r c e , w h i c h p o i n t s in t h e s a m e d i r e c t i o n as t h e a n t e r i o r part o f t h e b o d y . T h i s f o r c e is u s e d t o r e a c c e l e r a t e . I n a l i n e a r s i t u a t i o n , a d o r s a l f o r c e is w a s t e f u l h y d r o d y n a m i c a l l y b e c a u s e of t h e h e a v e (a d o r s o - v e n t r a l t r a n s l a t i o n m o v e m e n t ) t h u s c r e a t e d . In o r d e r to c o r r e c t t h e h e a v e a n d m a i n t a i n a rectilinear p a t h , t h e a n i m a l h a s t o s p e n d e n e r g y c o r r e c t i n g its t r a j e c t o r y by m o v i n g its h e a d a n d n e c k ( a s n o t e d a t t h e e n d o f a f e w t u r n s I r e c o r d e d — s e e F i g . 1 0 ) . A s p r e v i o u s l y m e n t i o n e d , C a l i f o r n i a s e a lions a s k e d to s w i m linearly a g a i n s t a c u r r e n t u s e d t h e p a d d l e p h a s e t o p r o d u c e m o s t o f t h e t h r u s t ( F e l d k a m p , 1 9 8 7 a ) . D u r i n g this p h a s e , t h e m a i n c o m p o n e n t o f t h e t h r u s t f o r c e is d i r e c t e d f o r w a r d , w h i c h limits v e r t i c a l m o v e m e n t s . In  the  limited s p a c e o f a s w i m mill, it m a k e s m o s t s e n s e for t h e a n i m a l to u s e t h e p a d d l e p h a s e a s m u c h a s p o s s i b l e . A g a i n , this s u g g e s t s t h a t otariids m o d i f y t h e i r s t r o k e c y c l e , i.e. e m p h a s i s i n g t h e t h r u s t production of o n e phase over the other, depending on their intended s w i m m i n g trajectory.  Finally, in a m a n o e u v r i n g s i t u a t i o n , t h e p o w e r p h a s e n o t o n l y p r o d u c e s t h r u s t , b u t a l s o p l a y s a n i m p o r t a n t role in c h o o s i n g t h e final s w i m m i n g d i r e c t i o n . For e x a m p l e , t h e s e a lion c a n p e r f o r m m o r e t h a n a 180 d e g r e e t u r n if it d e l a y s t h e o n s e t o f t h e p o w e r p h a s e a n d m a i n t a i n s t h e d o r s a l a r c h l o n g e r . C o n v e r s e l y , if t h e a n i m a l m a i n t a i n s a low b o d y c u r v a t u r e a n d p e r f o r m s a f l i p p e r s t r o k e e a r l y o n , it will t u r n less t h a n 180 d e g r e e s .  E a c h b o d y m a r k e r ( s h o u l d e r s , C G , hips) w a s s e e n to f o l l o w a slightly d i f f e r e n t t r a j e c t o r y , w h i c h w a s reflected in t h e different s p e e d profiles (Figs 8 , 12). T h e m i n i m u m s p e e d o f e a c h b o d y m a r k e r w a s r e a c h e d b e f o r e t h e m i d d l e o f their r e s p e c t i v e c u r v e d t r a j e c t o r y . F o r t h e s h o u l d e r s a n d t h e C G , t h e  50  m i n i m u m w a s r e a c h e d b e f o r e t h e start of t h e p o w e r p h a s e . T h e hips o n t h e o t h e r h a n d , r e a c h e d t h e i r m i n i m u m s p e e d later, a p p r o x i m a t e l y a t t h e s t a r t o f t h e p o w e r p h a s e .  T h e m i n i m u m s p e e d of t h e s h o u l d e r s a n d t h e c e n t r e of g r a v i t y w a s o f t e n f o l l o w e d by a b o u t o f c o n s t a n t o r e v e n slightly i n c r e a s i n g s p e e d (i.e. a ' f l a t ' m i n i m u m ) , d u r i n g w h i c h t h e p e c t o r a l flippers w e r e a b d u c t e d a n d m o t i o n l e s s . T h i s period s o m e t i m e s c a r r i e d t h r o u g h t o t h e e a r l y s t a g e o f t h e p o w e r p h a s e . T h i s implies t h a t t h e lift f o r c e g e n e r a t e d off t h e still, a b d u c t e d p e c t o r a l flippers c a n p r o d u c e t h r u s t b e f o r e t h e start o f t h e  power phase. As the animal arches dorsally, the  ( r e p r e s e n t a t i v e of t h e p o s t e r i o r e n d o f t h e b o d y ) m o v e o u t s i d e o f t h e t u r n a n d their  trajectory  d e p a r t s f r o m t h e t r a j e c t o r y o f t h e o t h e r t w o m a r k e r s . T h i s is a r e s u l t o f t h e r o t a t i o n a l created  by t h e  d i s p l a c e m e n t of  the  h e a d inside t h e  turn  (for  more  on  the  hips  effect  moment of  head  d i s p l a c e m e n t o n rotation m o m e n t , s e e T u c k e r , 2 0 0 0 ) . A s t h e b o d y r e g a i n s a s t r a i g h t position at t h e e n d o f t h e t u r n , t h e t r a j e c t o r y o f t h e hips c r o s s e d t h e t w o o t h e r t r a c k s ( F i g . 8 ) , a n d t h e posterior e n d of t h e b o d y t h e r e f o r e a c c e l e r a t e d f a s t e r t h a n t h e s h o u l d e r s a n d C G .  T h e d o r s a l f l e x i o n a n d t h e e x t e n d e d pelvic flippers limit t h e o u t w a r d m o t i o n o f t h e p o s t e r i o r e n d o f t h e b o d y a n d r e d u c e t h e overall d e c e l e r a t i o n . If t h e a n i m a l d o e s not t a k e t h e s e m e a s u r e s a n d r e m a i n s in a s t r a i g h t p o s i t i o n , t h e hips will rotate o u t w a r d s , t h u s e x p o s i n g t h e b o d y t o a n i m p o r t a n t c r o s s f l o w a n d p r e s s u r e d r a g m u c h like t h e b o t t l e n o s e d o l p h i n s d u r i n g a p i n w h e e l  manoeuvre  ( M a r e s h e t a l . , 2 0 0 4 ) . I n t h e c a s e o f a rigid o b j e c t , t h e p r e s s u r e d r a g c r e a t e d o v e r t h e b o d y ' s profile r e d u c e s both t h e t r a n s l a t i o n a l a n d t h e rotational v e l o c i t i e s b e c a u s e it a c t s o n t h e e n t i r e length o f t h e a n i m a l , o n b o t h s i d e s o f t h e c e n t r e o f m a s s . A s t h e t u r n s b e c o m e t i g h t e r a n d f a s t e r , t h e rotational a n d t r a n s l a t i o n a l v e l o c i t i e s i n c r e a s e a s d o e s t h e o u t w a r d slip o f t h e p o s t e r i o r e n d , t h u s i n d u c i n g a high p r e s s u r e d r a g , w h i c h s c a l e s w i t h t h e s q u a r e of s p e e d .  In t h e c a s e o f t h e flexible Steller s e a lion, t h e relationship b e t w e e n initial s p e e d , t u r n i n g r a d i u s , a n d p o s t e r i o r slip is not a s s t r a i g h t f o r w a r d a s w i t h a rigid b o d y . In fact, s u c h a c l e a r r e l a t i o n s h i p b e t w e e n these three variables would only be expected w h e n the animal s w i m s close to  its  maximum  s w i m m i n g c a p a b i l i t y , a n d c a n n o t a r c h its b a c k a n y f u r t h e r . I d i d not o b s e r v e this in m y  study  51  b e c a u s e t h e t e s t a n i m a l s d i d not m a k e u s e of their m a x i m u m d o r s a l f l e x i o n a n d d i d not s w i m at their m a x i m u m s w i m m i n g c a p a b i l i t y ( p e r s o n a l o b s e r v a t i o n ) . N e v e r t h e l e s s , it is c l e a r t h a t t h e d o r s a l f l e x i o n a l l o w s a n i m a l s to t a k e a d v a n t a g e o f t h e rotational m o m e n t g e n e r a t e d o v e r t h e a n t e r i o r part of t h e b o d y w i t h o u t suffering f r o m t h e a d d e d p r e s s u r e d r a g o v e r t h e p o s t e r i o r e n d .  Stelle et a l . ( 2 0 0 0 ) d e t e r m i n e d t h a t t h e a v e r a g e coefficient o f h y d r o d y n a m i c d r a g o f 6 Steller s e a lions p a s s i v e l y gliding w a s 0 . 0 0 4 6 ( r e f e r e n c e d to t o t a l w e t t e d s u r f a c e a r e a ) , 0 . 0 4 4 ( r e f e r e n c e d t o volume  2 7 3  ) , o r 0 . 0 8 0 ( r e f e r e n c e d to frontal s u r f a c e a r e a ) at a m e a n R e y n o l d s n u m b e r o f 5 . 5 2 X 1 0 . 6  R e c e n t l y , B l a k e a n d C h a n (in r e v i e w ) d e v e l o p e d a s i m p l e d y n a m i c m o d e l , w h i c h predicts t h e s p e e d of a s u b m e r g e d a q u a t i c a n i m a l p e r f o r m i n g a n u n p o w e r e d t u r n a s a f u n c t i o n o f t i m e . By c o m b i n i n g this m o d e l w i t h t h e d a t a o f S t e l l e e t a l . ( 2 0 0 0 ) , I p r e d i c t e d a t h e o r e t i c a l d e c e l e r a t i o n o f 0 . 4 m / s a n initial s p e e d o f 3 m / s ( F i g . 11). H o w e v e r , m y e x p e r i m e n t a l indicates d e c e l e r a t i o n s of 1.6 m / s , l . l m / s , a n d 0 . 8 m / s 2  hips  respectively,  all  followed  by  2  an  important  2  2  at  d a t a for t h e s a m e initial s p e e d  for t h e s h o u l d e r s , c e n t r e o f gravity a n d  acceleration  (for  average  acceleration  and  deceleration values, see Table 4).  T h e r e are a n u m b e r of potential explanations for the substantial divergence b e t w e e n observations a n d m o d e l predictions o f d e c e l e r a t i o n rates. First, t h e o b s e r v e d s e a lion t u r n s w e r e o n l y u n p o w e r e d d u r i n g t h e first half o f their m a n o e u v r e s . D u r i n g t h e s e c o n d half o f t h e m a n o e u v r e s , t h e s e a lions made  u s e of t h e c e n t r i p e t a l  acceleration and performed  a flipper  stroke to create a  positive  a c c e l e r a t i o n t h a t t h e m o d e l d o e s not a c c o u n t for. S e c o n d , a s B l a k e a n d C h a n (in r e v i e w ) m e n t i o n , t h e coefficient of d r a g ( C ) u s e d in t h e m o d e l e q u a t i o n s d o e s not i n c l u d e t h e effect o f d r a g o n t h e d  c o n t r o l s u r f a c e s . G i v e n t h e size a n d position o f t h e c o n t r o l s u r f a c e s o f t h e S t e l l e r s e a lion d u r i n g a t u r n , t h e a m o u n t o f d r a g t h e y i n d u c e is potentially i m p o r t a n t . T h i r d , t h e C o b t a i n e d f r o m i n s t a n t a n e o u s rates of d e c e l e r a t i o n d u r i n g assumed that C  d  d  u s e d in t h e m o d e l w a s  linear g l i d e s . In  o t h e r w o r d s , it w a s  is t h e s a m e d u r i n g a m a n o e u v r e a n d a l o n g a rectilinear s w i m m i n g p a t h . D u r i n g a  p a s s i v e g l i d e , a s e a lion is m o t i o n l e s s , k e e p i n g its pectoral flippers a d d u c t e d a l o n g its v e n t r a l f l a n k s , a n d r e d u c i n g its pelvic flippers a r e a . T h i s c o n f i g u r a t i o n m i n i m i z e s h y d r o d y n a m i c d r a g (Stelle et a l . ,  52  2 0 0 0 ) b e c a u s e it e x p o s e s a m i n i m u m a m o u n t o f s u r f a c e a r e a to friction d r a g , a n d t h e s e a lion maintains a streamlined shape. During a manoeuvre however, a n animal generates a side force to d e v i a t e f r o m its linear t r a j e c t o r y a n d this c a n o n l y b e a c c o m p l i s h e d by a b o d y a n d / o r a m o v e m e n t . It is t h e r e f o r e likely t h a t C  d  fin  is g r e a t e r d u r i n g a m a n o e u v r e d u e t o t h e s e m o v e m e n t s  ( H u g h e s a n d Kelly, 1 9 9 6 ; Stelle et a l . , 2 0 0 0 ; W e b b , 1 9 9 1 ) . U n f o r t u n a t e l y , m o s t o f t h e literature a v a i l a b l e o n t h e coefficient of d r a g is related t o p a s s i v e d r a g (Bilo a n d N a c h t i g a l l , 1 9 8 0 ; F e l d k a m p , 1987b; Williams and K o o y m a n , 1985).  T h e d i f f e r e n c e of d r a g e x p e r i e n c e d by a s w i m m i n g s e a lion in a p a s s i v e g l i d e a n d in a m a n o e u v r e t h a t i n v o l v e s b o t h b o d y a n d f l i p p e r m o v e m e n t s is illustrated in t h e d i f f e r e n t d e c e l e r a t i o n rates o f Figs 11 a n d 1 2 . T h e b o d y a n d flipper m o v e m e n t s c h a n g e t h e s t r e a m l i n i n g o f t h e a n i m a l (its s h a p e in relation t o t h e i n c o m i n g f l o w ) , t h u s i n f l u e n c i n g t h e v a l u e o f C , a n d m a k i n g t h e a v e r a g e d e c e l e r a t i o n d  rate a t least 3 t i m e s g r e a t e r t h a n p r e d i c t e d by t h e m o d e l . T h e s p e e d v a r i a t i o n o f a s l o w t u r n a n d a fast turn both diverge f r o m the predictions of the theoretical m o d e l (Fig. 12) e v e n though  the  m o v e m e n t s o f t h e flippers a r e not a s p r o n o u n c e d d u r i n g t h e s l o w e r m a n o e u v r e . T h i s s u g g e s t s t h a t body movements are mostly responsible for the deceleration at the beginning of the turn. Blake and C h a n (in r e v i e w ) s h o w e d t h a t their d y n a m i c m o d e l predicts t h e d e c e l e r a t i o n o f accurately. movements,  T. albacares and  cannot  is a  perform  specialized thunniform cruiser, which very  tight t u r n s  (0.47L).  In  other  Thunnus albacares  has limited w o r d s , their  body and  fin  unpowered  manoeuvres a r e closer to a linear glide than the m a n o e u v r e s of the flexible s e a lions. This explains w h y t h e d y n a m i c m o d e l y i e l d e d a better fit o f t h e t h u n n i f o r m s t h a n it d i d f o r S t e l l e r s e a lions.  T h e n o r m a l a c c e l e r a t i o n ( a ) o f t h e s h o u l d e r s a n d t h e c e n t r e o f g r a v i t y o f t h e Steller s e a lions n  s t a r t e d i n c r e a s i n g d u r i n g P h a s e 1 of t h e m a n o e u v r i n g s e q u e n c e (i.e. h e a d d i s p l a c e m e n t , roll, a n d f l i p p e r a b d u c t i o n ) . It c o n t i n u e d to i n c r e a s e until r e a c h i n g a m a x i m u m at t h e o n s e t o f t h e p o w e r p h a s e of t h e p e c t o r a l f l i p p e r s , a n d c a m e b a c k c l o s e t o z e r o d u r i n g P h a s e 5 o f t h e s e q u e n c e , at t h e e n d of t h e p o w e r p h a s e . T h e m a x i m u m v a l u e of n o r m a l a c c e l e r a t i o n n e v e r e x c e e d e d 2 0 m / s  2  53  ( a p p r o x i m a t e l y 2 g ) , a v a l u e m u c h l o w e r t h a n p r e v i o u s l y e v a l u a t e d f o r o t a r i i d s ( n o t a b l y 5 . 1 3 g for t h e C a l i f o r n i a s e a lion - Fish e t a l . , 2 0 0 3 ) .  T h e d i f f e r e n c e b e t w e e n t h e s e m a x i m u m a c c e l e r a t i o n v a l u e s in different s p e c i e s o f otariids m i g h t be e x p l a i n e d in t w o w a y s . First, m y e x p e r i m e n t a l d e s i g n m a y not h a v e f o r c e d t h e Steller s e a lions to r e a c h their  highest  performance  level — a n d e v e n t h e  upper 2 0 % of m y  d a t a m a y not  be  representative of the extreme manoeuvring and s w i m m i n g capabilities of the animals (personal observations).  Up  to  some  extreme  values, swimming  speed and  turning  radius  are  under  b e h a v i o u r a l c o n t r o l a n d t h u s a r e principally i n f l u e n c e d by m o t i v a t i o n l e v e l s . T h i s m a y e x p l a i n w h y Fish et a l . ( 2 0 0 3 ) o b t a i n e d h i g h e r relative velocities a n d t u r n i n g radii f o r C a l i f o r n i a s e a lions ( F i g . 13) e v e n t h o u g h t h e i r e x p e r i m e n t a l s e t u p w a s similar to o u r s .  U  2  A s e c o n d p o s s i b l e e x p l a n a t i o n is t h a t Fish et al. ( 2 0 0 3 ) u s e d t h e e q u a t i o n a  = a  c  average turning  speed to  calculate centripetal acceleration (equal to the  n  = —  and the  normal acceleration,  a s s u m i n g t h e t u r n f o l l o w s a circular t r a j e c t o r y ) . G i v e n t h a t t h e m a x i m u m v a l u e s o f a  n  are reached  d u r i n g t h e t i m e o f m i n i m u m s p e e d , t h e e q u a t i o n will t e n d to o v e r e s t i m a t e t h e m a x i m u m c e n t r i p e t a l acceleration for average values of speed. Based on the difference between the average speed and t h e m i n i m u m s p e e d o f t h e 195 t u r n s I o b s e r v e d , I a s s e s s t h a t t h e o v e r e s t i m a t i o n o f m a x i m u m a  c  was about 3 0 % .  T h e m a x i m u m tangential acceleration (a ) closely followed the m a x i m u m of a , thereby t  n  illustrating  t h e d u a l role o f t h e p o w e r p h a s e — to reposition t h e b o d y at t h e e n d o f t h e t u r n a n d a c c e l e r a t e . T h e hips a l s o f o l l o w e d t h e s a m e p r o g r e s s i o n after a s h o r t d e l a y (as s e e n by t h e p e a k in a f o l l o w i n g t h e n  p e a k in a ) . In all o f t h e t u r n s t h a t I r e c o r d e d , t h e m a x i m u m n o r m a l a c c e l e r a t i o n w a s s y s t e m a t i c a l l y t  g r e a t e r t h a n t h e m a x i m u m t a n g e n t i a l a c c e l e r a t i o n . In o t h e r w o r d s , it t o o k a g r e a t e r f o r c e  to  m a i n t a i n a c u r v e d t r a j e c t o r y a n d resist slip t h a n t o r e a c c e l e r a t e . In t h e a b s e n c e o f d o r s a l k e e l s o r s t r u c t u r e s t h a t help to c r e a t e this i m p o r t a n t c e n t r i p e t a l f o r c e , s e a lions (as w e l l a s p e n g u i n s - H u i ,  54  1 9 8 5 ) d e p e n d o n t h e i r large pectoral f l i p p e r s , w h i c h e x p l a i n s w h y t h e y h a v e t o roll t o a p p r o p r i a t e l y position t h e s e c o n t r o l s u r f a c e s .  CONCLUSIONS Steller s e a lions u s e t h e s a m e t e c h n i q u e t o t u r n a s h a s b e e n r e p o r t e d f o r a n o t h e r o t a r i i d , t h e California s e a lion (Fish et a l . , 2 0 0 3 ) . H o w e v e r , significant n e w i n f o r m a t i o n w a s o b t a i n e d a b o u t t h e t e c h n i q u e s e m p l o y e d b y o t a r i i d s b y j o i n t l y a n a l y s i n g b o t h k i n e m a t i c a n d kinetic p a r a m e t e r s o f t h e t u r n s p e r f o r m e d by Steller s e a lions.  First, t h e d a t a s h o w t h a t o t a r i i d s a r e o n e o f t h e m o s t m a n o e u v r a b l e m a r i n e m a m m a l s e v e n t h o u g h t h e y d e p l o y a c o n s i s t e n t t u r n i n g t e c h n i q u e . C h a n g e s in initial s p e e d o r t u r n i n g a n g l e d o not affect t h e t u r n i n g s e q u e n c e . R a t h e r , S t e l l e r s e a lions v a r y t h e d u r a t i o n a n d i n t e n s i t y o f m o v e m e n t s w i t h i n the  turning  sequence, and  thus  have  an  almost  infinite  number  of  options  to  determine  directionality.  S e c o n d , t h e majority o f o b s e r v e d s e a lion t u r n s h a d a V - s h a p e s p e e d p a t t e r n , w h i c h reflects t h e partially p o w e r e d m a n o e u v r i n g s t y l e o f otariids. D o r s a l f l e x i o n a n d a b d u c t i o n m o v e m e n t s o f t h e large pectoral flippers inflict m o r e d r a g c o m p a r e d t o a linear g l i d e d u r i n g t h e first s t a g e s of a m a n o e u v r e . T h i s t r a n s l a t e s into i n c r e a s e d d e c e l e r a t i o n , w h i c h b e c o m e s less p r o n o u n c e d o n c e t h e p e c t o r a l flippers a r e fully a b d u c t e d . T h e m a x i m u m c e n t r i p e t a l a c c e l e r a t i o n is r e a c h e d slightly after t h e m i n i m u m s p e e d a t t h e b e g i n n i n g o f t h e p o w e r p h a s e of t h e p e c t o r a l f l i p p e r s t r o k e .  Finally, t h e  p o w e r p h a s e of t h e p e c t o r a l flipper s t r o k e c a u s e s t h e a n i m a l to a c c e l e r a t e at t h e e n d o f t h e t u r n .  A third notable finding w a s that m y a s s e s s m e n t of flipper m o v e m e n t of otariids during a turn ( p e c t o r a l p r o p u l s i o n ) d i f f e r e d significantly f r o m t h e results o b t a i n e d by F e l d k a m p ( 1 9 8 7 a ) f o r linearly s w i m m i n g a n i m a l s . I f o u n d t h a t t h e a b d u c t i o n o f t h e p e c t o r a l flippers ( a l s o k n o w n a s t h e r e c o v e r y p h a s e ) by a n i m a l s p r e p a r i n g for a t u r n did not p r o d u c e t h r u s t a s i n d i c a t e d by t h e c o n s i d e r a b l e  55  deceleration I observed. However, Feldkamp (1987a) found that thrust w a s generated during  the  recovery phase.  D u r i n g t h e s e c o n d part o f t h e t u r n , I f o u n d t h a t m o s t o f t h e t h r u s t w a s p r o d u c e d d u r i n g t h e p o w e r p h a s e of t h e flipper s t r o k e . Little t h r u s t w a s c r e a t e d d u r i n g t h e p a d d l e p h a s e , t o t h e point t h a t it w o u l d be s k i p p e d a l t o g e t h e r d u r i n g a d o u b l e s t r o k e . In c o n t r a s t , F e l d k a m p ( 1 9 8 7 a ) f o u n d t h a t t h e paddle phase produced  m o s t of t h e t h r u s t g e n e r a t e d  over the entire  s t r o k e c y c l e in  linearly  s w i m m i n g a n i m a l s . T h i s c o u l d s u g g e s t t h a t Steller s e a lions a n d C a l i f o r n i a s e a lions h a v e a different s t r o k e t e c h n i q u e . H o w e v e r , g i v e n t h e o r i e n t a t i o n of t h e f o r c e s d u r i n g t h e s t r o k e c y c l e a n d t h e g r e a t mobility o f t h e t h r u s t - p r o d u c i n g a p p e n d a g e s , it is m o r e likely t h a t both s p e c i e s m o d i f y their s t r o k e t e c h n i q u e a c c o r d i n g to t h e situation (i.e. linear v e r s u s c u r v e d s w i m m i n g  trajectory).  A final n o t e w o r t h y f i n d i n g s t e m m i n g f r o m m y d a t a is t h a t Steller s e a lions a r e not a s m a n o e u v r a b l e a s California s e a lions in t e r m s of pure t u r n i n g  p e r f o r m a n c e (Fish e t a l . , 2 0 0 3 ) . H o w e v e r  this  c o n c l u s i o n m a y n e e d f u r t h e r scrutiny g i v e n t h a t t h e t u r n i n g p e r f o r m a n c e o f t h e s e a lions in b o t h e x p e r i m e n t a l s e t u p s m a y h a v e d e p e n d e d heavily o n t h e m o t i v a t i o n level o f t h e s t u d y a n i m a l s .  56  REFERENCES Alexander, D. E. ( 1 9 9 0 ) . D r a g coefficients o f s w i m m i n g a n i m a l s : e f f e c t s o f u s i n g d i f f e r e n t r e f e r e n c e a r e a s . Biological Bulletin 179, 1 8 6 - 1 9 0 . Bilo, D. and Nachtigall, W. ( 1 9 8 0 ) . A s i m p l e m e t h o d t o d e t e r m i n e d r a g c o e f f i c i e n t s in a q u a t i c a n i m a l s . Journal of Experimental Biology 87, 3 5 7 - 3 5 9 . Blake, R. W. ( 1 9 7 7 ) . O n o s t r a c i i f o r m l o c o m o t i o n . Journal of the Marine Biological Association of the United Kingdom 57, 1 0 4 7 - 1 0 5 5 . Blake, R. W. ( 2 0 0 4 ) . Fish f u n c t i o n a l d e s i g n a n d s w i m m i n g p e r f o r m a n c e . Journal of Fish Biology65, 1193-1222.  Blake, R. W. and Chan, K. H. S. (in r e v i e w ) . A s i m p l e m o d e l o f t h e d y n a m i c s o f t u r n i n g in a q u a t i c a n i m a l s . Journal of Fish Biology. Blake, R. W., Chatters, L. M. and Domenici, P. ( 1 9 9 5 ) . T u r n i n g r a d i u s o f y e l l o w f i n t u n a (Thunnusalbacares) in u n s t e a d y s w i m m i n g m a n o e u v r e s . Journalof Fish Biology46, 5 3 6 - 5 3 8 . Domenici, P. ( 2 0 0 3 ) . H a b i t a t , b o d y d e s i g n a n d t h e s w i m m i n g p e r f o r m a n c e o f f i s h . In Experimental Biology Reviews. Vertebrate biomechanics and evolution, e d s V . L. Bels A . C a s i n o s a n d J . - P . G a s c ) , p p . 1 3 7 - 1 6 0 . O x f o r d : B I O S Scientific P u b l i s h e r s L t d .  Domenici, P. and Blake, R. W. ( 1 9 9 7 ) . T h e k i n e m a t i c s a n d p e r f o r m a n c e o f fish f a s t - s t a r t s w i m m i n g . Journal of Experimental Biology 100, 1 1 6 5 - 1 1 7 8 . Domenici, P. and Blake, R. W. ( 2 0 0 0 ) . B i o m e c h a n i c s in b e h a v i o u r . In Biomechanics in Animal Behaviour, e d s P. D o m e n i c i a n d R. W . B l a k e ) , p p . 1-17. O x f o r d : B I O S S c i e n t i f i c P u b l i s h e r s L t d . Domning, D. P. and De Buffrenil, V. ( 1 9 9 1 ) . H y d r o s t a s i s in t h e s i r e n i a : q u a n t i t a t i v e d a t a a n d f u n c t i o n a l i n t e r p r e t a t i o n s . Marine mammalscience!, 3 3 1 - 3 6 8 . Dudley, R. ( 2 0 0 2 ) . M e c h a n i s m s a n d implications of a n i m a l flight m a n e u v e r a b i l i t y . Integrative and Comparative Biology 42, 1 3 5 - 1 4 0 . English, A. W. ( 1 9 7 6 ) . L i m b m o v e m e n t s a n d l o c o m o t o r f u n c t i o n in t h e C a l i f o r n i a s e a lion (Zalophus californianus). Journal of Zoology, London 178, 3 4 1 - 3 6 4 . Feldkamp, S. D. ( 1 9 8 7 a ) . F o r e f l i p p e r p r o p u l s i o n in t h e C a l i f o r n i a s e a lion, Z a l o p h u s c a l i f o r n i a n u s . Journal of Zoology, London 212, 4 3 - 5 7 . Feldkamp, S. D. ( 1 9 8 7 b ) . S w i m m i n g in t h e C a l i f o r n i a s e a lion: m o r p h o m e t r i e s , d r a g a n d e n e r g e t i c s . Journal of Experimental Biology 131, 1 1 7 - 1 3 5 . Firth, H. R. and Blake, R. W. ( 1 9 9 1 ) . M e c h a n i c s of t h e startle r e s p o n s e in n o r t h e r n p i k e , Esox lucius. Canadian Journal of Zoology 69, 2 8 3 1 - 2 8 3 9 . Fish, F. E. ( 1 9 9 3 ) . I n f l u e n c e o f h y d r o d y n a m i c d e s i g n a n d p r o p u l s i v e m o d e o n m a m m a l i a n s w i m m i n g e n e r g e t i c s . Australian Journal of Zoology 42, 7 9 - 1 0 1 .  57  F i s h , F. E. ( 1 9 9 7 ) . B i o l o g i c a l d e s i g n s for e n h a n c e d m a n e u v e r a b i l i t y : a n a l y s i s o f m a r i n e m a m m a l  Tenth International Symposium on Unmanned Untethered Submersible Technology: Special Session on Bio-engineering Research Related to Autonomous Underwater  p e r f o r m a n c e . In  Vehicles, (ed. A . a . O N R ) . D u r h a m . F i s h , F. E. ( 2 0 0 2 ) . B a l a n c i n g r e q u i r e m e n t s for stability a n d m a n e u v e r a b i l i t y in c e t a c e a n s .  Integrative and Comparative Biology 4 2 , 8 5 - 9 3 .  F i s h , F. E., H u r l e y , J . a n d C o s t a , D. P. ( 2 0 0 3 ) . M a n e u v e r a b i l i t y by t h e s e a lion Zalophus  californ/anus. t u r n i n g p e r f o r m a n c e of a n u n s t a b l e b o d y d e s i g n . Journal of Experimental Biology 206,  667-674.  F i s h , F. E., I n n e s , S . a n d R o n a l d , K. ( 1 9 8 8 ) . K i n e m a t i c s a n d e s t i m a t e d t h r u s t p r o d u c t i o n o f swimming harp and ringed seals.  Journal of ExperimentalBiology137, 1 5 7 - 1 7 3 .  G e r s t n e r , C . L. ( 1 9 9 9 ) . M a n e u v e r a b i l i t y o f f o u r s p e c i e s o f c o r a l - r e e f fish t h a t d i f f e r in b o d y a n d pectoral-fin m o r p h o l o g y .  Canadian Journal of Zoology 77', 1 1 0 2 - 1 1 1 0 .  H a r p e r , D. G . a n d B l a k e , R. W . ( 1 9 9 0 ) . P r e y c a p t u r e a n d t h e f a s t - s t a r t p e r f o r m a n c e o f t h e rainbow trout 150,  Salmo gairdneriand t h e n o r t h e r n p i k e Esoxlucius. Journal of Experimental Biology  321-342.  H o e r n e r , S . F. a n d B o r s t , H . V . ( 1 9 7 5 ) . Fluid d y n a m i c lift. Brick T o w n , N . J . : M r s . Liselotte A . Hoerner. H o w l a n d , H . C. ( 1 9 7 4 ) . O p t i m a l s t r a t e g i e s for p r e d a t o r a v o i d a n c e : t h e relative i m p o r t a n c e o f s p e e d and  maneuverability.  Journal of Theoretical Biology47, 3 3 3 - 3 5 0 .  H u g h e s , N . F. a n d K e l l y , L. H . ( 1 9 9 6 ) . A h y d r o d y n a m i c m o d e l f o r e s t i m a t i n g t h e e n e r g e t i c c o s t o f s w i m m i n g maneuvers from a description of their geometry and d y n a m i c s .  Canadian Journal of  Fisheries and Aquatic Sciences 5 3 , 2 4 8 4 - 2 4 9 3 . H u i , C. A. ( 1 9 8 5 ) . M a n e u v e r a b i l i t y o f t h e H u m b o l d t p e n g u i n (Spheniscus humboldti) d u r i n g swimming.  Canadian Journal of Zoology 63, 2 1 6 5 - 2 1 6 7 .  L o u g h l i n , T. R., P e r e z , M . A . a n d M e r r i c k , R. L. ( 1 9 8 7 ) . Eumetopias jubatus. In Mammalian Species Account no.283, p p . 1-7: T h e A m e r i c a n Society of M a m m a l o g i s t s . M a r e s h , J . L., F i s h , F. E., N o w a c e k , D. P., N o w a c e k , S . M . a n d W e l l s , R. S . ( 2 0 0 4 ) . H i g h p e r f o r m a n c e t u r n i n g c a p a b i l i t i e s d u r i n g f o r a g i n g by b o t t l e n o s e d o l p h i n s  (Tursiops truncatus).  Marine mammal science 2 0 , 4 9 8 - 5 0 9 . M e r r i c k , R. L , C h u m b l e y , M . K. a n d B y r d , G . V . ( 1 9 9 7 ) . Diet d i v e r s i t y o f S t e l l e r s e a lions ( E u m e t o p i a s j u b a t u s ) a n d t h e i r p o p u l a t i o n d e c l i n e in A l a s k a : a potential r e l a t i o n s h i p .  Canadian  Journal of Fisheries and Aquatic Sciences 54, 1 3 4 2 - 1 3 4 8 . N a t i o n a l M a r i n e F i s h e r i e s S e r v i c e . ( 1 9 9 2 ) . R e c o v e r y P l a n f o r t h e S t e l l e r S e a L i o n (Eumetopias  jubatus). ( e d . Steller S e a Lion R e c o v e r y T e a m for t h e N a t i o n a l M a r i n e F i s h e r i e s S e r v i c e ) , p p . 9 2 . Silver S p r i n g , M a r y l a n d . N o r b e r g , U . a n d R a y n e r , J . M . V . ( 1 9 8 7 ) . E c o l o g i c a l m o r p h o l o g y a n d f l i g h t in b a t s ( M a m m a l i a : C h i r o p t e r a ) : W i n g a d a p t a t i o n s , flight p e r f o r m a n c e , f o r a g i n g s t r a t e g y a n d e c h o l o c a t i o n .  Philosophical Transactions of the Royal Society B 316, 3 3 5 - 4 2 7 .  58  Nowacek, D. P. (2002). Sequential foraging behaviour of bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, Fl. Behaviour 139, 1125-1145.  Ponganis, P. J., Ponganis, E. P., Ponganis, K. V., Kooyman, G. L., Gentry, R. L. and Trillmich, F. (1990). Swimming velocities in otariids. Canadian Journal of Zoology 6S, 21052112. Riedman, M. (1990). The Pinnipeds: Seals, Sea Lions, and Walruses. Berkeley, CA: University of California Press. Rosen, D. A. S. and Trites, A. W. (2004). Satiation and compensation for short-term changes in food quality and availability in young Steller sea lions (Eumetopias jubatus). Canadian Journal of Zoology %1, 1061-1069. Schrank, A. J., Webb, P. W. and Mayberry, S. (1999). How do body and paired-fin positions affect the ability of three teleost fishes to maneuver around bends? Canadian Journal of Zoology 77, 203-210. Sinclair, E. H. and Zeppelin, T. K. (2002). Seasonal and spatial differences in diet in the western stock of Steller sea lions {Eumetopias jubatus). Journal of Mammalogy S3, 973-990. Stelle, L. L. (1997). Drag and energetics of swimming in Steller sea lions (Eumetopias jubatus). In Department of Zoology, pp. 84. Vancouver: University of British Columbia. Stelle, L. L , Blake, R. W. and Trites, A. W. (2000). Hydrodynamic drag in Steller sea lions (Eumetopias jubatus). The Journal of Experimental Biology 203, 1915-1923. Tucker, V. A. (2000). Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient. Journal of Experimental Biology 203, 3733-3744. Walker, J. A. (2000). Does a rigid body limit maneuverability? Journal of Experimental 3391-3396. Wardle, C. S. (1975). Limit of fish swimming speed. Nature255,  Biology 203,  725-727.  Webb, P. W. (1977). Effects of median-fin amputation on fast-start performance of rainbow trout (Salmo gairdneri). Journal of Experimental Biology 6&, 123-135. Webb, P. W. (1978). Fast-start performance and body form in seven species of teleost fish. Journal of Experimental Biology 74, 211-226. Webb, P. W. (1983). Speed acceleration and maneuverability of 2 teleost fishes. Journal of Experimental Biology 102, 115-122. Webb, P. W. (1984). Body form, locomotion and foraging in aquatic vertebrates. American Zoologist24, 107-120. Webb, P. W. (1991). Composition and mechanics of routine swimming of rainbow trout, Oncorhynchus mykiss. Canadian Journal of Fisheries and Aquatic Sciences 48, 583-590. Weihs, D. (1973). The mechanism of rapid starting of slender fish. Biorheology 10, 343-350.  59  Weihs, D. ( 2 0 0 2 ) . Stability v e r s u s m a n e u v e r a b i l i t y Comparative Biology 42, 1 2 7 - 1 3 4 .  in a q u a t i c l o c o m o t i o n .  Integrative and  Williams, T. M. and Kooyman, G. L. ( 1 9 8 5 ) . S w i m m i n g p e r f o r m a n c e a n d h y d r o d y n a m i c c h a r a c t e r i s t i c s of h a r b o r s e a l s Phoca vitulina. Physiological Zoology58, 5 7 6 - 5 8 9 . Winship, A. J., Trites, A. W. and Calkins, D. G. lion. Journal of Mammalogy S2, 5 0 0 - 5 1 9 .  ( 2 0 0 1 ) . G r o w t h in b o d y size o f t h e Steller s e a  

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