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UBC Theses and Dissertations

Some effects of a unique hydroelectric development on the littoral \ benthic community and ecology of… Mylechreest, Peter 1978

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SOME EFFECTS OF A UNIQUE HYDROELECTRIC DEVELOPMENT ON THE LITTORAL BENTHIC COMMUNITY AND ECOLOGY OF TROUT IN A LARGE NEW  ZEALAND LAKE  BY  PETER MYLECHREEST B.A.  (1958);  CAMBRIDGE  M.B.,  B,. C h i r .  UNIVERSITY,  (1962)  England  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE  REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN  THE  FACULTY OF GRADUATE STUDIES (Department o f  We a c c e p t to  THE  this  thesis  the required  Zoology) as  conforming  standard  UNIVERSITY OF BRITISH April, (c}  COLUMBIA  1973  P e t e r M y l e c h r e e s t , 1978  In p r e s e n t i n g t h i s  thesis  an advanced degree at the L i b r a r y s h a l l I  f u r t h e r agree  for scholarly by h i s of  this  written  make i t  freely available  that permission  for  the requirements  Columbia,  I agree  r e f e r e n c e and  f o r e x t e n s i v e copying o f  this  It  for financial  is understood that copying or gain s h a l l  permission.  The U n i v e r s i t y o f B r i t i s h 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5  Columbia  for  that  study. thesis  purposes may be granted by the Head of my Department  Depa rtment  6  f u l f i l m e n t of  the U n i v e r s i t y of B r i t i s h  representatives. thesis  in p a r t i a l  or  publication  not be allowed without my  ABSTRACT A three year study hydroelectric and  (1974-1977) examined t h e e f f e c t s  development  on t h e l i t t o r a l  e c o l o g y o f brown t r o u t  (.Salmo g a i r d n e r i I s l a n d o f New  Richardson)  dam.  landslide,  which  I t s development  unique being  i n that  and  rainbow  i n L a k e Waikaremoana on  formed  created  over  2 000  a natural  for hydroelectric  the lake  l e v e l was  trout  the  y e a r s ago r o c k and  purposes  initially  most s i g n i f i c a n t m o r p h o m e t r i c  electric  development  littoral  a r e a , and  North  by  a  earth-fill  i n 1946  lowered  was  rather  than  level  has been r e v e r s e d .  The  lake  level  Hydroelectric  but t h e i r  invertebrate  i n summer and  drawdown i s now  i n t h e deep l i t t o r a l  with a f a l l i n g but instead  lake  level  of  fluctuations  level  and  fauna are adapted  a rising  lake  level  distrito a i n winter.  c o n c u r r e n t w i t h an upward The  i n summer no increasing  i s s u b j e c t e d to deeper  the  seasonal p e r i o d i c i t y  s e a s o n a l changes i n the depth  o f some a n i m a l s d u r i n g w i n t e r .  animals  of lake  g r e a t e r than the amplitude of  fluctuations,  b u t i o n o f the l i t t o r a l falling  great loss  lake.  r e c e n t years the amplitude  lake  hydro-  t h e c r e a t i o n o f deep w i n d i n g c h a n n e l s a t  has n o t been s i g n i f i c a n t l y natural  changes f o l l o w i n g  were a d i s p r o p o r t i o n a t e l y  s t r e a m mouths e n t e r i n g t h e In  tion  L.)  raised. The  the  trutta  fauna  Zealand.  L a k e Waikaremoana was massive  (Salmo  invertebrate  of  maximum d e n s i t y longer light  migraof  coincides  penetration,  submergence and  reduced  water t r a n s p a r e n c y The e n t on  small juvenile  the  utilization  t o summer s t o r a g e and  of water.  large, old trout  littoral  space,  o f the  littoral  food resources with i n c r e a s i n g  and  size.  and  unnatural  The  fluctuations  littoral  s p a c e and  capacity  o f the  the o v e r a l l  combined e f f e c t s  and  a r e most d e p e n d -  shallow  age  to  due  t h e r e i s an i n c r e a s i n g  of the morphometric  i n lake l e v e l ,  f o o d r e s o u r c e s , has  lake for trout r e d u c t i o n i n the  through  decreased  to a degree out  changes  reduction of the c a r r y i n g  of proportion  s u r f a c e area of the  lake.  - iv-  TABLE OF CONTENTS Page Abstract  i i  Table o f Contents L i s t o f Tables L i s t of Figures Acknowledgements  iv v i i viii x.  I.  INTRODUCTION  1...  II.  STUDY AREA  4  A.  LAKE WAIKAREMOANA AND CATCHMENT  4  Geographical l o c a t i o n and geology  4  Lake formation  6  The catchment  7  N a t i v e f i s h and i n t r o d u c e d s p e c i e s . . . . 9  III.  B.  HYDROELECTRIC DEVELOPMENT  10  C.  LAKE LEVEL FLUCTUATIONS  13  Amplitude  13  Seasonal p e r i o d i c i t y  15  Major c y c l e  18  Rate o f r i s e and f a l l  18  MATERIALS AND METHODS A.  20  PHYSICAL  20  Surveys o f the l a k e shore  20  Planimetry  . 21  Water transparency and temperature....  22  Lake l e v e l , power g e n e r a t i o n and rainfall  23  - v Page B.  LITTORAL BENTHOS  23  Ekman d r e d g e  sampling  23  procedure  27  Statistical  IV.  C.  ZOOPLANKTON AND LARVAL F I S H  27  D.  TROUT  29  N e t t i n g programme  29  Stomach a n a l y s i s  31  RESULTS  32  A.  32  PHYSICAL Morphometric  changes.  Thermal c o n d i t i o n s transparency  32  and w a t e r 34  D i s s o l v e d oxygen  36  B.  AQUATIC MACROPHYTES  36  C.  LITTORAL BENTHOS  39  Sampling v a r i a b i l i t y  39  Depth d i s t r i b u t i o n . .  43  Composition  45  S e a s o n a l changes distribution  48  Molluscs  52  Odonata  D.  i n depth  and L e p i d o p t e r a  52  Trichoptera  56  Chironomids  58  TROUT  58  Composition o f the t o t a l catch  58  Spatial  60  distribution  - v iPage Stomach a n a l y s i s  63  Limnetic  66  food  resources  Recruitment o f j u v e n i l e s t o lake  68  Condition  69  factor  V. ... DISCUSSION  73  A.  MORPHOMETRIC  CHANGES  73  B.  LAKE LEVEL FLUCTUATIONS  74  Seasonal p e r i o d i c i t y  74  E f f e c t s on l i g h t p e n e t r a t i o n primary producers  78  Major c y c l e  80  Rate o f r i s e C.  and  and f a l l  LITTORAL INVERTEBRATE Quantitative  81 FAUNA  losses  82 84  S e a s o n a l c h a n g e s i n d e p t h d i s t r i b u t i o n 85 Qualitative D.  losses  88  TROUT  89  Species composition  89  Spatial  90  segregation  Effects of hydroelectric on  a v a i l a b l e space  Food and c o n d i t i o n Effects on f o o d VI. VII. VIII.  development 93  factor  of hydroelectric resources  SUMMARY MANAGEMENT IMPLICATIONS LITERATURE CITED  94 development 95 97 99 100  - v i i -  L I S T OF TABLES  TABLE I. II.  III.  IV.  PAGE  The Morphometry o f L a k e Waikaremoana l e v e l 6 08 m e t r e s a . s . l . ) . . .  Cat  lake 8  The s e a s o n a l p e r i o d i c i t y o f l a k e l e v e l f l u c t u a t i o n s b e f o r e and a f t e r h y d r o e l e c t r i c development  17  M o r p h o m e t r i c c h a n g e s i n L a k e Waikaremoana f o l l o w i n g h y d r o e l e c t r i c development o f t h e lake  33  S a m p l i n g v a r i a b i l i t y w i t h i n t h e drawdown Cat 2-3m), m i x e d ( a t 5-6m), and N i t e l l a ( a t 1112m) z o n e s a t H a u t a r u k e Bay  40  - viii  L I S T OF  -  FIGURES  Figure  Page  .1. L a k e Waikaremoana and c a t c h m e n t streams . ..  showing  the  inflowing 5  2. The o u t l e t o f L a k e Waikaremoana b e f o r e and h y d r o e l e c t r i c development  after 12  3. L a k e l e v e l f l u c t u a t i o n s i n L a k e Waikaremoana f r o m 1931 - 1976. From d a t a p r o v i d e d by t h e New Z e a l a n d E l e c t r i c i t y Department  14  4. The p e r i o d i c i t y o f l a k e l e v e l f l u c t u a t i o n s i n L a k e Waikaremoana b e f o r e and a f t e r h y d r o e l e c t r i c d e v e l o p ment. Mean m o n t h l y r a i n f a l l (Onepoto) and mean m o n t h l y power g e n e r a t i o n ( K a i t a w a )  16  5. L a k e l e v e l f l u c t u a t i o n s i n L a k e Waikaremoana, and s i x m o n t h l y r a i n f a l l (.Onepoto) and power g e n e r a t i o n ( K a i t a w a ) 1961-1976  19  6. Lake. Waikaremoana s h o w i n g s h o r e l i n e g e o l o g y , l i t t o r a l , b a t h y m e t r y and s t a t i o n l o c a t i o n s  25  lost  7. D i a g r a m m a t i c t r a n s e c t s of., a) t h e l i t t o r a l zone a t H a u t a r u k e Bay - b e n t h o s s a m p l i n g s t a t i o n and b i the n e t t i n g s t a t i o n s showing the p o s i t i o n i n g o f t h e gillnets  26  8. The n e t u s e d f o r s a m p l i n g l a r v a l  28  fish  9. T h e r m a l c o n d i t i o n s , w a t e r t r a n s p a r e n c y , and l a k e i n L a k e Waikaremoana O c t o b e r 1974 - J u l y 1977  level 35  10. The t e m p e r a t u r e and d i s s o l v e d o x y g e n p r o f i l e s i n L a k e Waikaremoana t o w a r d s t h e end o f t h e p e r i o d o f t h e r m a l s t r a t i f i c a t i o n 1975  37  11. The d e p t h d i s t r i b u t i o n o f t o t a l a n i m a l s , m o l l u s c s , i n s e c t s and o l i g o c h a e t e s i n t h e l i t t o r a l zone a t H a u t a r u k e Bay  44  12. The c o m p o s i t i o n H a u t a r u k e Bay  46  of the l i t t o r a l  invertebrate  13. S e a s o n a l c h a n g e s i n t h e d e p t h d i s t r i b u t i o n o f a n i m a l s a t H a u t a r u k e Bay  fauna a t total 49  - ix -  Figure 14.  Page  S e a s o n a l changes i n the depth d i s t r i b u t i o n o f moll u s c s , i n s e c t s and o l i g o c h a e t e s a t H a u t a r u k e Bay  51  S e a s o n a l changes i n t h e d e p t h d i s t r i b u t i o n g a s t r o p o d s and b i v a l v e s a t H a u t a r u k e Bay  of 53  S e a s o n a l changes i n the depth d i s t r i b u t i o n and L e p i d o p t e r a a t H a u t a r u k e Bay  of  17. S e a s o n a l c h a n g e s i n t h e d e p t h d i s t r i b u t i o n T r i c h o p t e r a a t H a u t a r u k e Bay  of  15. 16.  18.  S e a s o n a l changes.'in t h e d e p t h d i s t r i b u t i o n omids a t H a u t a r u k e Bay  19. The c o m p o s i t i o n o f t h e t o t a l g i l l n e t s from b o t h s t a t i o n s , s i z e and m a t u r i t y  Odonata 55 57  of  chiron59  c a t c h of t r o u t i n the according to species, 61  20. The l e n g t h f r e q u e n c y d i s t r i b u t i o n s o f t r o u t c a u g h t i n g i l l n e t s i n t h e drawdown zone, i n t h e deep l i t t o r a l zone and i n t h e l i m n e t i c zone, f r o m b o t h s t a t i o n s  62  21. The c o m p o s i t i o n o f t h e d i e t s t r o u t i n L a k e Waikaremoana  65  22.  o f brown and  rainbow  S e a s o n a l c h a n g e s i n t h e s i z e and numbers o f l a r v a l s m e l t and l a r v a l b u l l i e s , and i n t h e numbers o f D a p h n i a i n L a k e Waikaremoana 67  23. The l e n g t h f r e q u e n c y d i s t r i b u t i o n s o f r a i n b o w t r o u t c a u g h t i n g i l l n e t s d u r i n g e a c h 2-monthly s a m p l i n g ( O c t o b e r 1975 - F e b r u a r y 1976) 24.  The mean c o n d i t i o n f a c t o r o f r a i n b o w t r o u t t o s i z e and m a t u r i t y  70  in relation 71  25. The s e a s o n a l p e r i o d i c i t y and a m p l i t u d e o f t h e n a t u r a l f l u c t u a t i o n s i n l a k e l e v e l i n a)_ L a k e B l a s j o n , n o r t h e r n Sweden b) L o c h Lomond, S c o t l a n d and c). L a k e Waikaremoana  75  26. The n a t u r a l and r e g u l a t e d l a k e l e v e l L a k e B l a s j o n and L a k e Waikaremoana  77  fluctuations in  27. The d e p t h d i s t r i b u t i o n o f t h e b o t t o m f a u n a i n L a k e s B l a s j o n and A n k a r v a t t n e t , and i n Lake Waikaremoana....  83  - x -  ACKNOWLEDGEMENT  I would l i k e Wildlife,  t o t h a n k Mr. P . J . B u r s t a l l ,  Rotorua,  who was t h e d r i v i n g  Waikaremoana s t u d y , Zealand W i l d l i f e  and t h e r e m a i n d e r  S e r v i c e , Rotorua  Conservator of  force behind the of the s t a f f  Conservancy,  o f t h e New  for their  support. I am i n d e b t e d t o D r . M.A. identification  Chapman f o r h e r h e l p  o f the benthic invertebrates;  Ms. L. T i e r n e y , and Mr. S. P u l l a n sampling;  Mr. R. G i l l  o u t scuba  f o r h i s assistance with the netting  D. P a t t e r s o n f o r m a k i n g p o s s i b l e  Squadron  the a e r i a l  survey  Leader of the  t h e a n g l e r s and a n g l i n g c l u b s o f t h e G i s b o r n e ,  W a i r o a , Hawkes Bay a n d Manawatu D i s t r i c t s tion;  D r . P. Coleman,  for carrying  programme; No. 3 S q u a d r o n , R.N.Z.A.F. and  shoreline;  with  Mr. J . I r w i n o f t h e New  Zealand  for their  coopera-  Oceanographic  Institute  f o r p r o v i d i n g me w i t h a c o p y o f h i s , a t t h e t i m e  unpublished,  bathymetry  o f the T o u r i s t  o f L a k e Waikaremoana; Mr. L . S . D e n n i s  H o t e l C o r p o r a t i o n , Mr. J o h n S c o t t , a r c h i t e c t , of  t h e Urewera N a t i o n a l Park  f o r h e l p w i t h accomodation  t h e many p r o b l e m s w h i c h a r i s e remote  from  living  and w o r k i n g  and  in a  area.  This financial and  and t h e s t a f f  s t u d y c o u l d n o t have b e e n c a r r i e d support  I would l i k e  at a l l times,  from  t h e New  out without the  Zealand E l e c t r i c i t y  t o t h a n k them f o r t h e i r  Department,  h e l p and c o o p e r a t i o n  and f o r p r o v i d i n g me with, e s s e n t i a l  d a t a on  - xi -  lake-level, of  rainfall,  power g e n e r a t i o n  t h e Waikaremoana Power I would p a r t i c u l a r l y  G. N o r t h c o t e , years, helpful thesis.  f o r h i s help  and D r . P.A.  and e n g i n e e r i n g  aspects  Scheme. like  t o t h a n k my  and p a t i e n c e  s u p e r v i s o r , D r . T.  during  L a r k i n and D r . J.D. M c P h a i l  c r i t i c i s m and a d v i c e  during  the past  five  for their  the p r e p a r a t i o n o f t h i s  -  1  -  INTRODUCTION  The tion of  development of a l a k e  usually involves  the  land.  lake  l e v e l with  But,  i n the  o f a dam ural  for  was  rock  slide,  the  not  and  c o n s t r u c t i o n o f a dam,  f l o o d i n g of  required.  which occurred  recognized  over  initially  1966).  stages  The  first  frequently  (Axelsson fish  as  a result  of a massive  merged t e r r e s t r i a l  feeding  f i s h of  1963,  Nilsson  transitory, 1958,  was  increased  the  raised. three  to the  1964).  lasting  planktonic  and  the  at best  1963).  of  This  has  r e l e a s e of n u t r i e n t s from and  soil  (Rawson, 1 9 5 8 ) ,  the  first  2-5  availability  to  invertebrates  by  (Campbell the  i n p r o d u c t i v i t y - during  the  bottom(.Campbell  1957,  second  sub-  population  stage i s u s u a l l y  years  I t i s followed  i n the  -  production  growth r a t e s  consequent r e d u c t i o n  But  (Rzoska  "damming-up e f f e c t "  Campbell  submerged t e r r e s t r i a l  depression  than being  increased  F r o s t 1956,  nat-  land-  unique i n t h a t  - the  a  I t s development  u s u a l l y pass through  and  ( E l d e r 1965)  Rzoska 1966).  general  lakes  vegetation  i n s p a c e and fish  ago.  lowered r a t h e r  of these stages  p a r t been a t t r i b u t e d  of  construction  b e e n f o r m e d by  2000 y e a r s  Rodhe 1964)  density  surrounding  f o l l o w i n g h y d r o e l e c t r i c development  (Runnstrom 1951,  increase  raising  L a k e had  associated with  1961,  low-lying  genera-  The  e a r t h - f i l l dam  l e v e l was  and  c a s e o f L a k e Waikaremoana, t h e  In temperate r e g i o n s  in  the  h y d r o e l e c t r i c p u r p o s e s i n 1946  lake  is  f o r h y d r o e l e c t r i c power  only Stube  stage -  which the  a  inorganic  -  2 -  sediments u n d e r l y i n g the s o i l s  o f the inundated  land are 0  eroded  and t h e new  littoral  T h i s p r o d u c e s an a v a l a n c h e the  deeper  littoral  As t h e new passes  into  ivity.  effect  littoral  zones  - a gradual  sediments s t a r t  extent lakes  rooted  seldom r e g a i n t h e i r  R z o s k a 1966, L i n d s t r o m In s o u t h e r n may  occur  after  latitudes years  zones.  level  t o some  However, t h e s e h y d r o e l e c t r i c CRawson  1958,  reservoirs  year  the onset  of this  recovery  period of depression, be d e l a y e d  and a t h i g h e r  f o r up t o 25-30  (Beckman 1 9 6 6 ) .  entered  later)  into  a depression  s h o u l d be w e l l i n t o  The i n i t i a l  f i s h e r i e s management  T h i s p r e s s u r e was  futility  the " t h i r d  stage"  i n the t r o u t  effect"  I t probably  s t a g e , b u t by now  deterioration  to i n c r e a s i n g pressure  liberation  a "damming-up  f o l l o w i n g h y d r o e l e c t r i c development.  directly  recovery.  the  recover  former p r o d u c t i v i t y  (>50°N) r e c o v e r y may  immediately  rise  i n product-  and r e g i m e o f l a k e  L a k e Waikaremoana d i d n o t e x p e r i e n c e  years  the lake  1973).  Russian a 6-10  into  up i n t h e p r o f u n d a l  a q u a t i c m a c r o p h y t e s may  i n the l i t t o r a l  1965).  1973) .  stabilize  recovery  to build  zone, and d e p e n d i n g upon t h e e x t e n t fluctuations,  (.Lindstrom  zones p h y s i c a l l y  stage  (Grimas  o f i n o r g a n i c sediments  and p r o f u n d a l  the t h i r d  Organic  zones a r e u n s t a b l e  (.some 3 0  of gradual fishery  gave  f r o m r e g i o n a l a n g l i n g c l u b s on  authorities  t o take  remedial  f r e q u e n t l y i n t h e f o r m o f demands  o f l a r g e numbers o f h a t c h e r y - r e a r e d  f o r the  trout.  o f s t o c k i n g thousands of f r y o r f i n g e r l i n g s  action.  The i n such  -  hydroelectric  lakes  Zealand W i l d l i f e  3 -  i s discussed  S e r v i c e , who  by  are  Elder  (1965).  responsible  The  f o r the  New manage-  ment o f L a k e Waikaremoana, w i s e l y  r e s i s t e d t h e s e demands  instead  (made p o s s i b l e by  i n s t i g a t e d a 3 year study  f r o m t h e New out  Zealand E l e c t r i c i t y  between A u g u s t  s t u d y was  to gain  1974  and  ment.  Some o f  the  Particular 1. of  the  The lake  2.  a t t e n t i o n was  level,  a l t e r e d seasonal  distribution  of the  and  little  limnology  hydroelectric  seasonal  of the  trout fishery  this  thesis.  lowering  on  development.  Lake B l a s j o n  This  the  although there  fauna,  depth  the  f o r the  trout  period  the  Sweden by  i s a smaller the  and  of  dis-  or  before  overcome t o  some  hydroelectric usxng a  (Lake A n k a r v a t t n e t ) as  (Lake W a i k a r e i t i )  level  CGeen 1 9 7 4 ) ,  ecology  from the  considered  lake  changes i n the  p r o b l e m was  i n northern  . T h i s a p p r o a c h was  the  studies  (1961) i n h i s s t u d i e s o f  nearby, undeveloped lake  of  trout.  most s u c h  o f L a k e Waikaremoana  regulated  catchment  this  to  periodicity  a v a i l a b l e data  Grimas  its  basis of  invertebrate  ecology  as w i t h  d e g r e e by  study, but  paid  to the  littoral  feeding  Unfortunately,  study.  purpose of  and  in relation  the  The  carried  impacts of h y d r o e l e c t r i c develop-  f i n d i n g s form the  fluctuations  t h e r e was  1977.  morphometric changes r e s u l t i n g from the  The  tribution  August  the  grant  D e p a r t m e n t ) , w h i c h was  a b e t t e r u n d e r s t a n d i n g o f the  o f L a k e Waikaremoana and  a  and  a  similar,  "before"  L a k e Waikaremoana  undeveloped  dissimilarities  lake were  within too  - 4 -  great to use t h i s lake f o r comparative Conclusions  ("before") s t u d i e s .  r e g a r d i n g the e c o l o g i c a l s i g n i f i c a n c e o f the im-  pacts o f h y d r o e l e c t r i c development on Lake Waikaremoana are t h e r e f o r e somewhat s p e c u l a t i v e i n nature.  STUDY AREA LAKE WAIKAREMOANA Geographical  AND CATCHMENT  l o c a t i o n & geology  Lake Waikaremoana, with a maximum depth o f 248 metres and  a s u r f a c e area o f 51 square k i l o m e t r e s , i s the deepest,  but not the l a r g e s t lake on the North I s l a n d - o f New The  Zealand.  lake l i e s a t an e l e v a t i o n o f 610 metres above sea l e v e l  i n the Urewera Mountains, a t L a t i t u t d e 38° 45'S and Longitude 177°  05'E (Figure 1).  Zealand  T h i s area o f the North I s l a n d o f New  l i e s d i r e c t l y over the p l a t e margins o f the P a c i f i c  and A u s t r a l i a n p l a t e s , a t e c t o n i c a l l y a c t i v e subduction  zone  w i t h moderately frequent earthquakes and an a c t i v e v o l c a n i c b e l t — 100 kms. to the west.  Convergence o f the p l a t e s i s  t a k i n g p l a c e a t a r a t e o f 3-7 cms. a year The  (Minster:  e t a l 1974).  s h o r e l i n e and b a s i n of the lake are composed o f T e r t -  i a r y sedimentary rocks, 10-22 m i l l i o n years o l d (N.Z. Geol. Survey).  They c o n s i s t o f a l t e r n a t i n g s t r a t a o f sandstone and  a s o f t , l i g h t grey-coloured ing  siltstone  s t r a t a vary from a few centimetres  thick.  They a r e t i l t e d ,  a southeasterly d i r e c t i o n  (papa).  These a l t e r n a t -  t h i c k to over 3 0 metres  d i p p i n g a t an angle o f about 18° i n (Carter 1951).  In the northwest  FIGURE 1. Lake Waikaremoana and catchment showing the i n f l o w i n g streams. Bars a c r o s s the l a r g e r streams i n d i c a t e the l o c a t i o n of w a t e r f a l l s i m p a s s a b l e t o upstream m i g r a t i n g t r o u t .  -  corner  of  the  catchment the  6 -  rocks  are  older, with  o f J u r a s s i c greywacke i n t h e  Hopuruahine catchment  logical  o f pumice  thick)  Survey) . blankets  An the  overlay  sedimentary rocks  outcroppings (N.Z.  Geo-  (.approximately 3 m e t r e s t h r o u g h o u t much o f  the  catchment.  Lake  formation L a k e Waikaremoana was  off  t h e Ngamoko Range  Panekiri bluffs  f o r m e d by  ( F i g u r e 1)  obliterating  the  o l d Waikare-Taheke R i v e r  ing  a massive n a t u r a l rock  This  damming b a c k o f  similar electric gradual The  had  and  previously  earth^fill  lake's Jolly The  natural level For  i n t o the  and  lake  many o f  day  age  as  was  the  standing  dam  the which creat-  (Anderson  1948).  created  lake  a  much more r e c e n t man-made h y d r o -  than the  dam  has  trees of  a much more  man-made v a r i e t y .  this  stumps i n t h e  now  form  the  drowned f o r e s t lake-bed.  It  perwas  t h i s drowned f o r e s t t h a t  determined - approximately  220 0 y e a r s  (.Dr.  pers.comm.).  outflow  rise  this  dam  f o r e s t e d v a l l e y s , w h i c h were f l o o d e d ,  to t h i s  V.H.  flowed, thus  the Waikare-Taheke R i v e r  through r a d i o a c t i v e carbon d a t i n g of the  slumped down a g a i n s t  r i v e r - r e s e r v o i r s , a l t h o u g h the slope  broke  a deep n a r r o w g o r g e , t h r o u g h  i n morphometry t o t h e  lake basin, sist  and  a l a n d s l i d e , which  was  (Figure  l a r g e l y through subsurface 2),  sufficiently  reason  the  lake  and  only  o c c a s i o n a l l y d i d the  to form a s u r f a c e level  leaks  overflow  remained e i t h e r  in  the  lake  (.Figure 3) .  relatively  7 -  s t a b l e , o r e l s e had been r i s i n g only very g r a d u a l l y s i n c e the lake was formed, a l l o w i n g wave e r o s i o n t o work p e r s i s t e n t l y on the shores  over a r e s t r i c t e d v e r t i c a l range.  t e r r a c e s , which were carved  The wave-cut  from the open papa shores,  and the  d e l t a s , which were b u i l t a t the numerous stream mouths e n t e r i n g the l a k e , remained submerged, and c o n s i d e r a b l y i n c r e a s e d the .. area o f shallow continuous and  littoral  i n t h i s deep, s t e e p - s i d e d  lake.  A  s u r f a c e overflow would have caused r a p i d e r o s i o n  c u t t i n g down o f the l i p o f the dam, with a consequent pro-  g r e s s i v e lowering o f the lake l e v e l and " l o s s " o f these littoral  areas  (as occurs  i n most l a k e s ) .  shallow  Some o f the present  morphometric c h a r a c t e r i s t i c s are given i n Table 1.  The  catchment The  catchment of Lake Waikaremoana, which i s about 7 times  the area o f the l a k e , c o n s i s t s almost e n t i r e l y o f undisturbed beech f o r e s t and forms a small p a r t o f the Urewera N a t i o n a l Park.  The mean annual r a i n f a l l i s about 200-250 cms. Highway 38 passes through the catchment from the o u t l e t  along the e a s t e r n shores of the catchment.  o f the lake t o the n o r t h e r n  corner  A t Home Bay (Figure 1) and nearby a t A n i -  waniwa there are s i t u a t e d a t o u r i s t complex and the Park Headquarters r e s p e c t i v e l y .  These are the only permanent human  settlements w i t h i n the catchment. and others v i s i t  Trampers, fishermen,  hunters  the lake throughout the year, and up t o 500-10.00  v i s i t o r s per day stay a t these two l o c a t i o n s d u r i n g peak h o l i d a y  -  Table 1.  8 -  The Morphometry o f Lake Waikaremoana  (at l a k e  l e v e l 6 08 metres a s . 1. ) .  AREA OF CATCHMENT:  371 square k i l o m e t r e s  AREA OF LAKE:  51.4 square k i l o m e t r e s  LENGTH OF SHORELINE:  9 3.2 k i l o m e t r e s  SHORELINE DEVELOPMENT:  3.67  9  VOLUME OF LAKE: MAXIMUM DEPTH: MEAN DEPTH: RESIDENCE TIME:  4.76 X 10 248 metres 9 3 metres — 8 years  c u b i c metres  -  times  ( C h r i s t m a s and  septic  New  9  -  Year h o l i d a y s ) .  Sewage e f f l u e n t  tanks a t t h e s e s e t t l e m e n t s passes i n t o the  stream or  seeps d i r e c t l y  i n t o the  lake  i n the  from  Aniwaniwa  vicinity  o f Home  Bay.  Native  fish  and  Prior occurring  to  introduced  the  species  introduction  long-finned  eel  Giinther) .  T h e r e may  no  longer gain  development), but p r e s e n t i n the in  w e i g h t and  lake in  also  and  lake 40  a galaxid  o l d and  (up  to  years of  at  the  very  i n 1896  rainbow t r o u t  ( B u r s t a l l 1975).  m i g r a t o r y and  species  present,  large  a  bully  brevipinnis of  is  (since  fish  galaxids doubtful.  hydroelectric  specimens are  metres long,  14  still kgs.  age).  (Salmo t r u t t a L.)  1907  (Galaxias  lake  l e a s t 1.5  Brown t r o u t and  native  still  t h e i r p r e s e n c e now  access to  a few  only  which are  have b e e n o t h e r  B u r s t a l l pers.comm.), b u t can  the  (Anguilla d i e f f e n b a c h i i Gray),  (Gobiomorphus c o t i d i a n u s ) ,  Eels  trout,  i n L a k e Waikaremoana, and  were t h e  (P.  of  (Salmo g a i r d n e r i  There are  stream r e s i d e n t  were i n t r o d u c e d  now  to  the  Richardson)  well-established  (above-falls)  lake-  populations of  both  species. Smelt the  (Retropinna  lacustris  R o t o r u a L a k e s i n 194 8 t o  adverse e f f e c t s of sources of The  the  Stokell)  were i n t r o d u c e d  compensate f o r t h e  hydroelectric  d e v e l o p m e n t on  from  anticipated the  food  re^  trout.  adventive aquatic  weed, E l o d e a c a n a d e n s i s ,  has  been  -  present  10  -  i n Lake Waikaremoana s i n c e b e f o r e  1946  and  d i s t r i b u t e d throughout the l i t t o r a l areas of the  i s widely-  lake.  HYDROELECTRIC DEVELOPMENT Before  1946  generation  the T u a i power s t a t i o n , which commenced power  i n 1929,  had  operated  of water from the l a k e .  In 1946  which allowed  o n l y on the n a t u r a l  discharge  o u t l e t m o d i f i c a t i o n s began,  some c o n t r o l over the outflow  and  l a k e l e v e l of  Lake Waikaremoana, and made f e a s i b l e the s i t i n g o f another power-station  (Kaitawa) between the Lake and T u a i .  the lake l e v e l was  first  lowered by means of temporary siphons  by an e x c e p t i o n a l l y dry summer).  earth-fill  to connect with the i n t a k e s t r u c t u r e , which was behind a s i l l  i n t a k e s t r u c t u r e was  (Figure 2 ) .  dam,  installed in  c l o s e to the lake shore.  completed, the s i l l was  the i n t a k e to the lake  (aided  Twin tunnels were d r i v e n from  the Kaitawa s i d e through the n a t u r a l rock and  an e x c a v a t i o n  At  When the  removed opening  During maximum power gen-  e r a t i o n at Kaitawa the penstocks d e l i v e r water at a r a t e of approximately 30 cu. metres/sec. of t r o u t through the i n t a k e and grill  (4.8 cms  intake i n  gap)  was  I n i t i a l l y there was  a loss  down the penstocks, u n t i l a  i n s t a l l e d across  the mouth of  the  1959.  Between 1948 the subsurface successful.  and  1955  repeated  leaks i n the dam,  attempts were made to s e a l  but t h i s was  As some of the shallower  i t i e s w i t h i n the dam  c o l l a p s e d and  only  partially  leaks were s e a l e d ,  an e x t e n s i o n  of the  cav-  leakage  -  area  to about  o f the o r i g i n a l The 1954  twin  The  (approximately  concrete  channel  siphons  channel.  was  ered  with  were i n s t a l l e d  T h e s e can  be  used  1946  level  (Figure 3).  the  flood  initial  "dewatering"  and  T h i s has  and  The  downwards o n t o a s t e e p e r  will toral  cms,  to bypass i n the  sur-  event  of  T h e y were u s e d i n  35.4  dam,  and  Kaitawa  cu.  metres/sec. at a  b e e n done t o e n s u r e and  lake l e v e l  extensive areas  mouth d e l t a s .  b e e n no  third  beneath the  p r o t e c t i o n t o downstream l o w e r i n g of the  60  been m a i n t a i n e d  earth-fill  o f t h e o l d " d r o p - o f f " and  has  was  low-  stability  also i t provides areas. resulted  in  the  o f p r e v i o u s l y submerged w a v e - c u t t e r r a c e s a l o n g  the papa s h o r e s stream  flow of  l a k e l e v e l has  o f the n a t u r a l rock  This  c l o s e d down.  a recorded  Since  a measure o f  one  lowered  d e l i v e r w a t e r t o t h e T u a i power s t a t i o n  December 1976  leakage  flow).  K a i t a w a power s t a t i o n b e i n g  at  (Figure 2).  5 cu. metres/sec.  o l d surface overflow  face overflow and  -  i n t o deeper water occurred  reduced  in  11  significant  have r e s u l t e d  the  of the o l d shallow  lake l e v e l  i s now  i n the  littoral  zone has  been  average  slope.  i n a net  vicinity shifted  Assuming t h a t  change i n w a t e r t r a n s p a r e n c y , r e d u c t i o n i n the  littoral  there this  area  of the  have b e e n  carved  lit-  zone. At  the  stream  mouths deep c h a n n e l s  through  the  exposed d e l t a s .  influence of lake  level  w a t e r a t low  levels,  lake  These " g a u n t l e t s " a r e under  fluctuations, and  having  swiftly  f l o o d i n g back w i t h  the  flowing  sluggish  flow  TKE-HYDRO  ELECTRIC  FIGURE 2. The o u t l e t  DEVELOPMENT  "POST- H Y D R O E L E C T R I C  of Lake Waikaremoana b e f o r e and a f t e r h y d r o e l e c t r i c  development.  DEVELOPMENT  -  at high falls ing  lake  levels.  -  Because o f the  proximity  c l o s e t o t h e mouths o f t h e m a j o r i t y  the  lake  available  ( F i g u r e 1), the  of  of high  the  icularly  are  potentially  important  stream nursery  areas  as  enter-  streams  restricted.  spawning areas  f o r r a i n b o w t r o u t , whose e a r l y m i g r a n t  d e p e n d e n t on  water-  streams  accessible length of  t o spawning runs o f t r o u t i s g r e a t l y  These g a u n t l e t s  as  13  are  the  f r y are  partnot  brown t r o u t  fry.  LAKE LEVEL FLUCTUATIONS The (Figure 1.  continuous 3)  19 31  - 1946  3.  - Before  f l u c t u a t i o n s i n lake  - the  tric  d e v e l o p m e n t - an  The  level  f r o m 1931  reasonably  following  e a r l y period of extensive  periods: the  hydroelecfluctua-  level.  e a r l y 1960's - 1975  fluctuations  distinct  1975  level.  e a r l y 1960's - I m m e d i a t e l y  i n lake  to  h y d r o e l e c t r i c development -  1946  tions  of lake  b r e a k s down i n t o t h r e e  natural 2.  record  i n lake  - A recent  p e r i o d o f more  stabilized  level.  Amplitude During  the  recent  p o s t - h y d r o e l e c t r i c development  t h e mean a n n u a l a m p l i t u d e o f 2.8  metres, which i s not  annual amplitude now  of  2.5  the  much g r e a t e r metres  level.  level  fluctuations  level  was  t h a n t h e n a t u r a l mean  (Figure 3), but  f l u c t u a t e s a b o u t a mean l a k e  n a t u r a l mean l a k e  lake  period  4.7  the  lake  metres below  level the  mi  I-  •az '33 '34 as -3t 37  '» ' i v> \i 3  3  tu.  uu  ^ v W v  'so ; 5 i 'n ;n  fl 2 0 2 . 0 -  K E  2 0 i o •  L  ZOOO.  'it w;» ;i7  ' i i ; , ;i,c s  ;n  /tx ;t3 ; t » ;ts >  > T  >t /«  'TO  71 ^  ^  -74. 7s- - 7 .  E V E L (FEETfl-S-L-)  ERRLY  PRE-HYDROELECTRIC DEVELOPMENT  A M P L I T U D E M E A N A M P L I  O F  A N N U A L T U D E  PERIOD  L A K E  L E V E L  Z-5  D E V E  POST-HYDROELECTRIC LOPM ENT PERIOD  F L U C T U A T I O N S  RECENT POST-HYDROELECTRIC DEVELOPMENT  ( M E T R E S )  5-Z  M A X 1M U M  5-1  A N N U A L A M P L I T U D E M E A N L A K E L E V E L A - S L -  Z- 8  6l/f--0  FIGURE 3. Lake l e v e l f l u c t u a t i o n s i n Lake Waikaremoana from 1931 t o 1976. From data provided by the New Zealand E l e c t r i c i t y Department.  PERIOD  -  During  15 -  the e a r l y p o s t - h y d r o e l e c t r i c development  t h e mean a n n u a l a m p l i t u d e o f l a k e m e t r e s , w h i c h i s more t h a n t w i c e amplitude. viding for  During  this  a much h i g h e r  level  operating  (amplitude  Seasonal  3.6  p e r i o d o f t i m e Waikaremoana was  very  and f a l l  much l e s s  i n summer  (Table  lake  increased  ulated outflow to  now a l l o w  t h e New  (113 cms -  evapotranspiration  contribute to  an u n r e g u l a t e d  Zealand  (Figure 4).  periodicity,  i n summer and f a l l  outflow.  i n t h e dam and t h e r e g Electricity  t h e summer months f o r maximum  i n the winter,  tends t o r i s e  Although the  rainfall  surface, w i l l  s e a l i n g o f the leaks  natural seasonal  tended t o  t h e summer months, and i n -  i n summer - w i t h  s t o r e water d u r i n g  eration the  from t h e lake  level  partial  II).  level  (89 cms - O c t o b e r t o M a r c h i n c l u s i v e ) i s  t h a n t h e mean w i n t e r  evaporation  falling The  a.s.l.  metres).  from t h e f o r e s t e d catchment d u r i n g  a  pro-  hydro-  r a n g e i s now 607.8 - 611.4 m e t r e s  t o September i n c l u s i v e ) ,  creased  The p l a n n e d  h y d r o e l e c t r i c development the l a k e  i n winter  April  annual  p r o p o r t i o n o f t h e h y d r o e l e c t r i c power  mean summer r a i n f a l l not  5.2  periodicity  Before rise  f l u c t u a t i o n s was  t h e n a t u r a l mean  t h e N o r t h I s l a n d t h a n i t does now.  electric  period  T h i s has tended  so t h a t t h e l a k e i n winter  Department power g e n to reverse  level  (Table I I ) .  now  LAKE L E V E L F E E T A.S.L-  lozo  \j  2.010  1152.  rTTTT Tl 201  I /*? 1  I /95/f. I C ? ? ? I /<?S6 I/ ??? 1  5"3  TTTT7T1  1  1 1"  ITT Tl  'I r IT I I I  1  1 I1IIII  1  \l1S8  ITT TTTI  1  \ 19 St r  1 T T If 1  1  I/^O ITT II  1 I  rTTTTTT  0  M E A N  M 0 N T H L Y  KflI N F f l L L ( O N E P O T O )  2 . 0 0 0 f-  I  ISO  zooof I ^90  M E A N  M O N T H L Y POWER. <$ENERf\TION  FIGURE 4. The p e r i o d i c i t y of l a k e l e v e l f l u c t u a t i o n s i n Lake Waikaremoana b e f o r e and a f t e r h y d r o e l e c t r i c development. Mean monthly r a i n f a l l a t Onepoto (near the l a k e o u t l e t ) 1925-1974, and mean monthly power g e n e r a t i o n at the Kaitawa power s t a t i o n 1966-1975 - from data p r o v i d e d by the New Z e a l a n d E l e c t r i c i t y Department.  - 17 -  Table I I .  The seasonal p e r i o d i c i t y o f lake l e v e l b e f o r e and a f t e r h y d r o e l e c t r i c  Before C1932 - 1941)  LAKE LEVEL  fluctuations  development.  After (1966  - 1975)  INCIDENCE - NUMBER OF YEARS  RISING IN SUMMER  0  6  FALLING IN WINTER  1  6  FALLING IN SUMMER  8  0  RISING IN WINTER  7  2  LATE SUMMER EARLY WINTER  7  0  MID WINTER  3  1  LATE WINTER EARLY SUMMER  0  9  SEASONAL TIMING OF EXTREME LOW LAKE LEVELS  -  The  18  -  major c y c l e Before 194 6 the  lake l e v e l tended to f l u c t u a t e on  an  annual c y c l e about a reasonably steady mean annual lake  level.  Immediately f o l l o w i n g h y d r o e l e c t r i c development, although an annual c y c l e i s s t i l l  present,  years i s superimposed, and  a "major c y c l e " spanning  this i s s t i l l  present,  but  2-4  less  marked, i n the r e c e n t p o s t - h y d r o e l e c t r i c development p e r i o d (Figure 4) . The  major c y c l e i s a consequence of h y d r o e l e c t r i c  i z a t i o n of the  lake.  The  more or l e s s constant  util-  (or i n c r e a s -  ing) annual demand f o r power accentuates the e f f e c t s of years between successions 1964,  1969  - Figure  a succession Figure  of wet  5) predispose  years.  Dry w i n t e r s  dry  (e.g.  to extreme drawdown, and  o f wetter than average years  (e.g. 1970,  5) produce a "long term" upward t r e n d i n the  1971  -  lake  level.  Rate of r i s e and  fall  With the i n t a k e c l o s e d , the r a t e of r i s e i n lake for  any  given  i n f l o w w i l l have i n c r e a s e d  development due  at  since h y d r o e l e c t r i c  to the p a r t i a l s e a l i n g of the l e a k s , and  t o t a l absence, s i n c e 1946, The  of a s u r f a c e  generation  Kaitawa i s , of course, p a r t l y dependent on the  but averages about 3 cms/day, and may lake l e v e l s and  low  the  overflow.  r a t e of drawdown d u r i n g maximum power  6 cms/day a t low  level  inflows,  i n c r e a s e to about inflows.•  FIGURE 5. Lake l e v e l f l u c t u a t i o n s i n Lake Waikaremoana and s i x monthly r a i n f a l l (Onepoto) and power g e n e r a t i o n (Kaitawa) 1961 - 1976. The s i x monthly p e r i o d s are October t o March i n c l u s i v e (summer) and A p r i l to September i n c l u s i v e ( w i n t e r ) .  - 20 -  During maximum power g e n e r a t i o n a t Kaitawa from the l a k e , 30 c u b i c m e t r e s / s e c ,  the outflow  i s more than twice the  n a t u r a l outflow, when there was no s u r f a c e overflow, — 14 c u b i c metres/sec.  (Andejrson 194 8) .  MATERIALS AND METHODS  PHYSICAL Surveys o f the lake shore A e r i a l photographs  o f the l a k e taken b e f o r e and a f t e r  h y d r o e l e c t r i c development to  determine  (N.Z. A e r i a l Mapping.) were used  the p o s i t i o n s o f the pre-1946 and the 1971  s h o r e l i n e s o f the l a k e , 615.7 metres a . s . l . and 610.5 metres a.s.l. respectively  (an e l e v a t i o n d i f f e r e n c e o f 5.2 metres)  - and thus d e f i n e the shallow areas o f the pre-1946 l a k e bed, which were "dewatered" as a r e s u l t o f lowering the lake l e v e l with h y d r o e l e c t r i c development i n 19 46.  Henceforth  t h i s dewatered area o f the o l d lake bed w i l l be r e f e r r e d to  as the " l o s t l i t t o r a l " .  I t s lower boundary i s d e l i n e a t e d  on s h e l t e r e d areas o f the l a k e shore by the lower l i m i t s o f t e r r e s t r i a l v e g e t a t i o n (which are not e n t i r e l y s t a b l e ) , but i t does not i n c l u d e the shallow areas o f the p r e s e n t  lit-  t o r a l zone, which are i n t e r m i t t e n t l y exposed by hydroelectric  drawdown.  Work sheets showing the l o s t l i t t o r a l were prepared from the a e r i a l photographs  ( s c a l e 1:12,667), and, along  -  21  -  w i t h the r e l e v a n t s e c t i o n s of the 1971 a e r i a l  photograph,  were used d u r i n g an a e r i a l survey of the e n t i r e s h o r e l i n e by RNZAF I r o q u o i s h e l i c o p t e r i n September 1976. areas of the l o s t l i t t o r a l  Doubtful  on the a e r i a l photograph  areas i n shadow or covered by scrub) were checked  for  accuracy on the work sheets, and the nature of the t i o n cover of the l o s t l i t t o r a l was Two  Ce.g.  vegeta-  recorded.  separate s h o r e l i n e surveys have been c a r r i e d  by boat.  The  f i r s t , d u r i n g October  t o December 1974,  a d e t a i l e d survey of the present l i t t o r a l s h o r e l i n e geology,  out was  zone to r e c o r d  development of wave cut p l a t f o r m s , sub-  s t r a t e i n the shallow l i t t o r a l a q u a t i c macrophytes.  The  zone, and d i s t r i b u t i o n of  second  survey i n October  1976  was  c a r r i e d out to r e c o r d the geology of the pre-1946 s h o r e l i n e (Figure 6 ) .  Planimetry The bathymetry of Lake Waikaremoana with i s o b a t h s a t 20 metre depth i n t e r v a l s was the New  completed  Zealand Oceanographic  (Irwin 1977).  by Mr.  J . Irwin of  I n s t i t u t e i n September  T h i s c h a r t (scale 1:15,840) was  used  1972 to  measure the areas e n c l o s e d by the s h o r e l i n e and i s o b a t h s w i t h a p o l a r p l a n i m e t e r , the mean of three r e a d i n g s b e i n g taken. A second  c h a r t was  prepared  photograph and work sheets  from the 19 71  (.scale 1:12,667).  aerial T h i s was  used  -  to  measure t h e a r e a o f t h e l o s t  line  before The  depth  The using  and a f t e r h y d r o e l e c t r i c  areas  o f the l o s t  i n relation  littoral  to shoreline  area o f the present  a correction  the p r e s e n t  the l o s t zone  factor  littoral littoral  geology.  littoral  zone was e s t i m a t e d by  X  17  zone was e s t i m a t e d  Water t r a n s p a r e n c y  The a r e a o f  by a d d i n g  the area  0-20 m e t r e  s h o r e l i n e d e v e l o p m e n t and t h e  zone b e f o r e  and  and a f t e r from  hydroelectric  t h e above m e a s u r e m e n t s .  temperature  Temperature p r o f i l e s were r e c o r d e d  zone.  - 5 2 — — ) •  d e v e l o p m e n t were a l s o c a l c u l a t e d  i n t h e l a k e and w a t e r  a t l e a s t m o n t h l y between O c t o b e r  transparency 1974 and  1977 a t two s t a t i o n s - one a t t h e c e n t r e o f t h e main and t h e o t h e r  i n t h e Wairaumoana arm ( F i g u r e 1 ) .  T e m p e r a t u r e p r o f i l e s were r e c o r d e d to  0-20 m e t r e  t o (the area o f the p r e s e n t  area of the l i m n e t i c  lake,  and p r e s e n t  o f 17/20 on t h e measurements o f  L a k e volume, mean d e p t h ,  July  and l e n g t h o f s h o r e -  development.  a r e a o f t h e 0-20 m e t r e d e p t h  the pre-1946  depth  littoral  zone, and t h e l e n g t h o f s h o r e l i n e were m e a s u r e d i n  sections  of  22 -  55 m e t r e s d e p t h  model 51A. diameter  with  a t metre i n t e r v a l s  a Y.S.I, temperature/oxygen  down  meter,  Water t r a n s p a r e n c y was m e a s u r e d w i t h a 20 cm.  Secchi  disc.  -  23 -  Lake l e v e l , power g e n e r a t i o n and r a i n f a l l The c h a r t s of lake l e v e l f l u c t u a t i o n s were prepared from d a i l y records of the lake l e v e l kept by the New E l e c t r i c i t y Department. the  Zealand  A s t a f f gauge was i n s t a l l e d near  l a b o r a t o r y a t Home Bay f o r r e c o r d i n g lake l e v e l on samp-  l i n g days.  Data on r a i n f a l l a t Onepoto  (close to the lake  o u t l e t ) and power g e n e r a t i o n a t the Kaitawa power s t a t i o n were p r o v i d e d by the New  Zealand E l e c t r i c i t y  Department.  LITTORAL BENTHOS Ekman dredge sampling T r i a l Ekman dredge sampling was c a r r i e d out a t s c a t t e r ed  l o c a l i t i e s around the lake shore i n c o n j u n c t i o n w i t h the  s h o r e l i n e survey.  The s u b s t r a t e below the drawdown zone was  found to be more or l e s s uniform throughout the l i t t o r a l of  the l a k e , c o n s i s t i n g of f i n e papa s i l t , which was  Ekman sampling.  (e.g. stones, b o u l d e r s  bedrock o f sandstone and papa) i t was i m p o s s i b l e to sample  with an Ekman dredge. the  ideal for  The s u b s t r a t e i n the drawdown zone was much  more v a r i a b l e , and i n many i n s t a n c e s or  areas  In some s h e l t e r e d bays the s u b s t r a t e i n  drawdown zone a l s o c o n s i s t e d of f i n e papa s i l t ,  and such  was the case a t Hautaruke Bay which was chosen as the main sampling s t a t i o n  (Figure 6).  The t r a n s e c t a t Hautaruke Bay was c l e a r of s t a n d i n g or f a l l e n t r e e stumps, and the shallow l i t t o r a l  area c o n t a i n e d a  r e l a t i v e l y low growth o f macrophytes, such t h a t the macrophytes  - 24 -  and t h e i r u n d e r l y i n g s u b s t r a t e and r o o t s were o b t a i n e d i n each Ekman sample.  Scuba surveys were c a r r i e d out along the samp-  l i n g t r a n s e c t on three o c c a s i o n s , and d u r i n g one o f these the s l o p e of the l i t t o r a l  and lower l i m i t s o f the "mixed"  N i t e l l a zones were p l o t t e d  and  (Figure 7).  A second s t a t i o n c l o s e t o Home Bay was  sampled  regularly  i n c o n j u n c t i o n w i t h the Hautaruke Bay sampling programme to examine the p o s s i b l e e f f e c t s of sewage enrichment, but the r e s u l t s from t h i s second s t a t i o n are not presented here. The l i t t o r a l  i n v e r t e b r a t e fauna was  sampled over a 12  month p e r i o d  ( A p r i l 1975 - A p r i l 1976)  Sampling was  c a r r i e d out on a monthly b a s i s when p o s s i b l e  (July, October and December 1975 to  other  a t Hautaruke  Bay.  samplings were missed due  commitments).  On each sampling o c c a s i o n s i n g l e Ekman dredge  (.15 cm  X  15 cm ) samples were taken a t metre depth i n t e r v a l s from 1 down to 9 metres, and a t a l t e r n a t e metres between 9 and 2 0 metres, along the t r a n s e c t through the l i t t o r a l 7).  zone  (Figure  The depth i n t e r v a l s sampled were i n r e l a t i o n to a theo-  retical  "zero" lake l e v e l  (609.6 metres a . s . l . ) , which was  the  lower l i m i t o f t e r r e s t r i a l v e g e t a t i o n d u r i n g the sampling period.  Samples were washed and s i e v e d through a 0.8 mm  bronze  wire mesh and s o r t e d l i v e the day they were o b t a i n e d . In  a d d i t i o n to the monthly sampling, 10 r e p l i c a t e s were  taken a t each o f the three depths  (2, 5 and 12 metres), on  separate o c c a s i o n s , to examine sampling v a r i a b i l i t y i n the  OFFSHORE W » ONSHORE MerriNtr STATIONS  FIGURE 6. Lake Waikaremoana showing s h o r e l i n e geology, l o s t l i t t o r a l ( b l a c k ) , Bathymetry (20,100 & 200 metre i s o b a t h s from the bathymetry o f Lake Waikaremoana, I r w i n 1972), and s t a t i o n l o c a t i o n s .  /HYDROELECTRIC INTAKE  v  D  E P r H •M E T R E S  Io  7o  o  DRAWDOWN ^IZONE  30 DISTANCE  40 FROM  SHORE  -  50 METRES  ~~2o  7  DEEP LITTORAL  0  LIMNETIC  40 60 80-J  • S"0 FIGURE 7  DISTANCE  FROM  SHORE  -  M E T R E S ~  /2.00  Diagrammatic t r a n s e c t s of a) the l i t t o r a l zone a t Hautaruke Bay - benthos sampling s t a t i o n and, b) the n e t t i n g s t a t i o n s showing the p o s i t i o n i n g of the g ' i l l n e t s .  (RED  REEF)  - 27 -  drawdown, mixed and N i t e l l a  Statistical  zones  respectively.  procedure  A one-way non-parametric a n a l y s i s of v a r i a n c e (The K r u s k a l W a l l i s Test) was  used to t e s t f o r s i g n i f i c a n t d i f f e r e n c e s a t  p<0.05 i n the depth d i s t r i b u t i o n o f animals between seasons. Each sample c o l l e c t e d d u r i n g the monthly season was  samplings w i t h i n  used as a r e p l i c a t e o f the r e s p e c t i v e depth  ZOOPLANKTON AND  each  zone.  LARVAL FISH  Zooplankton samples were taken monthly between October 1975 and.August 1977 a t two s t a t i o n s - the Te Puna and Red offshore netting sites metres  (Figure 6 ) .  Two  v e r t i c a l h a u l s from 55  depth to the s u r f a c e were taken a t each sampling  on each sampling o c c a s i o n u s i n g a 25 cm nylon net Two  Reef  site  diameter Wisconsin  (10 meshes/mm). r e p l i c a t e samples  of the l a r v a l f i s h were o b t a i n e d a t  the same s t a t i o n s on the same o c c a s i o n s between August and August  19 77.  meshes/mm) was  A heavy-rimmed 55 cm  used, which sampled  down to a depth of 75 metres.  1976  diameter net (5.3  vertically  from the s u r f a c e  A t t h i s p o i n t the h a n d l i n e was  allowed to t i g h t e n , s n a r i n g the net, and t i l t i n g  the heavy rim  through 9 0 ° , and then immediately commencing the r e t r i e v e o f the c l o s e d net to the s u r f a c e Echosounder  (.Figure 8) .  runs o f approximately 400 metres were made a t  the o f f s h o r e n e t t i n g s t a t i o n s i n c o n j u n c t i o n w i t h the sampling  -  28 -  DIAMETER  FIGURE 8.  55 c m s .  The net used f o r s a m p l i n g l a r v a l  fish.  - 29 -  of the l a r v a l f i s h u s i n g a Furuno FG 11 Mark 3 echosounder (.50 khz) a t a s e t t i n g of gain 4.  Larval bullies  (Gobiomorphus  c o t i d i a n u s ) are i n a s i m i l a r s i z e range to Chaoborus  larvae  and w i t h t h e i r g a s - f i l l e d swim-bladders produce deep  scattering  l a y e r s on the echosounder t r a c i n g s s i m i l a r to those d e s c r i b e d f o r Chaoborus l a r v a e  (Northcote 1964).  L a r v a l smelt  (Retropinna  l a c u s t r i s S t o k e l l ) do not have a g a s - f i l l e d swim-bladder, and were found to produce no s c a t t e r i n g l a y e r on the echosounder on those sampling occasions when they were p l e n t i f u l , but l a r v a l b u l l i e s were absent. Daphnia i n the August 1976 to June 1977 Wisconsin samples were counted i n e n t i r e t y and together w i t h the remaining Wisc o n s i n samples have been examined Chapman o f Waikato  and counted by Dr.  M.A.  University.  The l a r v a l f i s h samples were counted i n e n t i r e t y and  total  l e n g t h measurements were made on each l a r v a l f i s h u s i n g a p r e c i s i o n c a l i p e r f i t t e d w i t h n e e d l e - p o i n t extensions to the measuring arms.  TROUT N e t t i n g programme Samples  of t r o u t were obtained by g i l l n e t t i n g a t i n t e r v a l s  of two months from October 1975 to December 1976.  Two  stations  were, used - one i n the main l a k e , Red Reef, and the other i n Wairaumoana, Te Puna (Figure 6 ) .  At each s t a t i o n separate nets  were s e t i n the l i m n e t i c zone, i n the deep l i t t o r a l  zone, and  - 30 -  i n the drawdown zone  (Figure 7 1 .  The o f f s h o r e net ( i n the l i m n e t i c zone) was s u r f a c e i n water 80-100 metres deep.  s e t a t the  T h i s net was  60 metres  long and 10 metres deep. An onshore net was s e t a t the s u r f a c e over the deep t o r a l i n water 10-15 metres deep; and 5 metres deep.  t h i s net was  lit-  60 metres long  Both t h i s onshore net and the o f f s h o r e net  c o n t a i n e d s i x 10 metre long panels of d i f f e r e n t mesh s i z e s : 2.5, 3.8, 5.1, 7.0,  7.6 and 10.2 cms  - monofilament nylon  netting. In a d d i t i o n two small nets - 15 metres long and 2.5 metres deep were used i n the drawdown zone, one w i t h a mesh s i z e of 2.5 cms.  the other w i t h a mesh s i z e o f 5.1 cms.  These s m a l l  nets i n the drawdown zone were not used d u r i n g the f i r s t  two  n e t t i n g s - i . e . October 1975 and December 1975. The nets were s e t b e f o r e dusk and l i f t e d a f t e r dawn the next day.  The d i s t r i b u t i o n of t r o u t w i t h i n and between the  nets was recorded; s p e c i e s , sex, l e n g t h , weight, and s t a t e of the gonads were recorded.  The e n t i r e stomach was removed  and  preserved i n 10% f o r m a l i n f o r l a t e r examination, together w i t h a sample of s c a l e s . The d i s t i n c t i o n between immature  f i s h and "previous spawn-  e r s " c o u l d be made i n most i n s t a n c e s by macroscopic examination of the gonads, but where there was any doubt s c a l e s were examined l a t e r f o r spawning marks, which were w e l l developed i n both rainbow and brown t r o u t .  -  31 -  Stomach a n a l y s i s The stomach was d i v i d e d a t the p y l o r i c f l e x u r e , and only the a n t e r i o r p o r t i o n was used f o r d e t a i l e d a n a l y s i s of the contents.  The s m a l l e r  X 20 - 40 m a g n i f i c a t i o n  food  items were examined and s o r t e d a t  under a d i s s e c t i n g microscope.  The  volume of the d i f f e r e n t food items was measured to the nearest 0.1 ml by displacement o f water i n a graduated g l a s s c y l i n d e r . The volume o f the p y l o r i c contents was a l s o measured to g i v e the t o t a l volume of the stomach contents.  -  -  32  RESULTS  PHYSICAL Morphometric The  Changes  initial  lowering  development reduced 51.4  km  the  (Table I I I ) .  2  a r e a was  lost.  The  pre-1946  sublittoral,  zone and  has  of the  lake l e v e l with h y d r o e l e c t r i c  s u r f a c e area of the 3.4  km  o f the pre-1946  2  estimated  shallow  gain i n l i t t o r a l  w h i c h i s now  become t h e  l a k e f r o m 54.8  lower  extremity  littoral  a r e a due  i n c l u d e d i n the  to  to  the  euphotic  o f t h e new  littoral,  2 was  approximately  reduction  i n the  T h e r e has reduction pared  altered  the  to  6.7.  1  :  the  deltas, terraces  on  littoral  limnetic  ratio  o f the and  (^ 17%  (cL 4%  area  to a s l i g h t l y the  to limnetic  slight  lesser  extent  the  this  has  from 1  littoral  :  5.8  area  loss of  a r e a a l o n g mixed  o f i s l a n d s , w h i c h now  been l i t t l e  was  stream-mouth  (Figure 6).  sandstone  as conv-  wave-cut  T h e r e has shores,  been and  shores.  r e d u c t i o n i n s h o r e l i n e d e v e l o p m e n t i s due  loss  T h e r e has  the  percentage  and  areas  r e d u c t i o n i n the  reduction in l i t t o r a l the  of  net reduction)  reduction)  exposed papa shores  reduction along  to the  the extent  l o s s o f p r e v i o u s l y submerged  no  part  area  o f the net  net  The  t h i s was  area.  of l i t t o r a l  little net  - and  t h e r e f o r e been a d i s p r o p o r t i o n a t e  Almost h a l f a result  km  limnetic  i n the  with  2.1  form  peninsulas.  change i n t h e mean d e p t h o f  the  in  -  33 -  Table I I I . Morphometric changes i n Lake Waikaremoana  following  h y d r o e l e c t r i c development o f the l a k e .  PREHYDROELECTRIC DEVELOPMENT  POSTHYDROELECTRIC DEVELOPMENT  LOSS  SURFACE AREA km2  54.8  51.4  3.4  (6.2%)  LENGTH OF SHORELINE (INCLUDING ISLANDS) km 103.5  93.2  10.3  (10%)  SHORELINE DEVELOPMENT MEAN DEPTH metres ESTIMATED AREA OF LITTORAL ZONE (0-17 METRES DEPTH) km 2  3.95 91.7  3.67 92.7  8.1  6.7  1.4  (17%)  46.7  44. 6  2.1  (.4,4%)  1 : 5.8  1  ESTIMATED AREA OF LIMNETIC ZONE (> 17 METRES DEPTH) km  2  RATIO OF AREAS OF LITTORAL:LIMNETIC  : 6.7  - 34 -  lake  (.in f a c t a s l i g h t i n c r e a s e ) , and  change i n t h e ion.  The  5%  r a t i o of reduction  insignificant 8  the  the  l a k e volume w i l l  residence  time of  significant  to  hypolimn-..  have had  an  approximately  years.  Thermal c o n d i t i o n s  & water  transparency  Thermal s t r a t i f i c a t i o n year, the  December t o May  years  years  1974  i n the  - 1977  d e p t h and  maximum s u r f a c e depth of tions  the  9).  Climatic variation  produced a p p r e c i a b l e strength  temperatures  of  (Figure  9).  apart  from the  the  littoral  zone, and  entire  littoral  zone i s e x p o s e d t o more o r  a mean o f relation  11.5  and  lake  parency occurred New  so  lies  below the  lower  t h r o u g h o u t most o f t h e  varied  less  the  limit  year  the  same  sea-  metres  with  the  f r o m 5.5  to  17.5  The  (Secchi  greatest after  reduction an  i n water  exceptional  1975/76, when h e a v y s e d i m e n t  cor-  disc  (Spearman's r a n k c o r r e l a t i o n  immediately  Year p e r i o d  months o f  There i s a s i g n i f i c a n t negative  level,  r = -0.61).  condi-  temperature.  readings  metres.  and  considerable  1-2  (p<0.01) between w a t e r t r a n s p a r e n c y  readings) ficient,  disc  The  first  of  Secchi  stratification  climate.  of thermal s t r a t i f i c a t i o n ,  changes i n water  between  g e n e r a l l y windy  period  sonal  the  d i f f e r e n c e s between  thermal  r e f l e c t s the  Waikaremoana  thermocline,  l a s t s f o r a b o u t 6 months o f  (Figure  thermocline  of the The  the  no  volumes o f e p i l i m n i o n  i n the  e f f e c t on  therefore  coeftrans-  flood loads  during and  much  |LOWER L I M I T OF THE L l T T O R f t L  OCT|NOV|DEC TAN|FEB |WflR|flPP, \n*Y | TUN |Tui |flufr|SE?T|OCT | NOV |D£C TflN |F EB /  WATER  TRANSPARENCY  1  7  5 THE  wew  I^Ar |TUN [TUL | US [5£PT| OCT | NOV \pjcTf\N I FEB JMflR | APR I MAY fruN |ruL |  11  7  6  /  7 7  ruR  FLOOD  SECCHI DISC READINGS  .DAMMINtr-UP  :,  THEORETICAL ~ZERO'LAKE L E V E L  ^DRAWDOWN  FIGURE 9. Thermal c o n d i t i o n s , water transparency  and lake l e v e l  October 1974 - J u l y 1977,  -  36 -  f l o a t i n g woody d e b r i s e n t e r e d t h e l a k e . The period  amplitude  of lake l e v e l  ( O c t o b e r 1974 - J u l y  fluctuations  1977) was  "damming up" above t h e t h e o r e t i c a l metres a . s . l . ) of  during the study  3.54 m e t r e s ;  1.60 m e t r e s  zero lake l e v e l  and 1.94 m e t r e s drawdown b e l o w .  (609.6  During  t h e 3 y e a r s 1975, 1976 and 1977, "damming up" w i t h  of t e r r e s t r i a l  v e g e t a t i o n and s o i l  or e a r l y w i n t e r , l a s t i n g  Dissolved Only  (August)  one r e l i a b l e  i n late April  d i s s o l v e d o x y g e n p r o f i l e was o b t a i n e d .  1975  (Figure  sounder  10).  o f thermal  observed  stratifica-  D i s s o l v e d oxygen i n t h e  down t o 55 m e t r e s d e p t h was c l o s e  f o r the temperatures  1957),  drawdown  oxygen  hypolimnion tion  Extreme  summer  1976.  T h i s was t o w a r d s t h e e n d o f t h e p e r i o d tion  flooding  occurred during late  f o r 2-5 months.  occurred during late winter  each  to f u l l  and t h e a l t i t u d e  (Hutchinson  b u t a m e t a l i m n i a l o x y g e n minimum was p r e s e n t . r u n s d u r i n g summer  concentrate  showed t h a t  the l a r v a l  a t the thermocline during the d a y l i g h t  satura-  Echo-  bullies hours.  AQUATIC MACROPHYTES Rooted 17.5 be  a q u a t i c macrophytes extended  metres a t Hautaruke  the lower  limit  the s u b l i t t o r a l and  scuba  Bay  (Figure  o f the l i t t o r a l  CMacan 1 9 5 1 ) .  7).  down t o a d e p t h o f T h i s was t a k e n t o  zone and commencement o f  During t r i a l  surveys a t several other l o c a t i o n s  Ekman  sampling  i n t h e main  lake,  -  TEMPERATURE <?  10  ll  37 -  VEQ-REES IX  CENTIGRADE 13  14-  '5"  FIGURE 10. The temperature and d i s s o l v e d oxygen p r o f i l e s i n Lake Waikaremoana 30th A p r i l 1975.  -  the at  lower about  toral  limit  o f r o o t e d m a c r o p h y t e s was a l s o  17-18 m e t r e s d e p t h ,  areas  38 -  found  t o occur  with the exception o f the l i t -  i n t h e p r o x i m i t y o f t h e m o t o r camp a t Home Bay,  where t h e l o w e r  limit  o c c u r r e d a t 15-16 m e t r e s  depth.  E x t r e m e drawdown d u r i n g t h e l a t e w i n t e r o f 19 7 3 ( F i g u r e 3) e x t e n d e d In  sheltered  continuous of  3 metres below t h e t h e o r e t i c a l  level  limit  littoral In  of this  areas  On s h o r e s  exposed t o  r o o t e d m a c r o p h y t e s were s p a r s e o r a b s e n t i n  less  t h e lower  demarcation  drawdown, w h i c h h a d b e e n t h e l o w e s t  s i n c e t h e w i n t e r o f 1969.  much wave a c t i o n  than ^  5 metres  depth.  "drawdown zone" s p a r s e clumps o f some n a t i v e  a q u a t i c m a c r o p h y t e s h a d s u r v i v e d i n most s h e l t e r e d the  i n t h e drawdown zone d u r i n g t h e s p r i n g  t h e h i g h e r l a k e l e v e l s o f 1975 a n d e a r l y lower  from  sp., M y r i o p h y l l u m  zone was t y p i c a l  examined, e x c e p t  invaded  limit  o f draw-  t h e r e was a  s p . and P o t a m o g e t o n  sp. with, a s p a r s e i n t e r m i n g l e d growth o f E l o d e a T h i s mixed  During  v e g e t a t i v e shoots.  t h e lower  (3 m e t r e s d e p t h ) down t o 8 m e t r e s d e p t h  "mixed zone" o f N i t e l l a  o f 1974.  1976 E l o d e a  drawdown zone b y means o f l a t e r a l  A t H a u t a r u k e Bay e x t e n d i n g down  areas o f  l a k e , b u t t h e a d v e n t i v e weed, E l o d e a c a n a d e n s i s , was n o t  found  the  level.  areas o f t h e l a k e t h e upper boundary o f  macrophyte beds p r o v i d e d a v e r y c l e a r  the lower  lake  littoral  zero lake  canadensis.  o f most o t h e r a r e a s o f t h e l a k e  i n the v i c i n i t y  o f Home Bay, where t h e m i x e d  zone was r e p l a c e d b y a d e n s e m o n o c u l t u r e  o f Elodea  canadensis.  -  From 8 m e t r e s d e p t h a monoculture During  of Nitella  the early  sion of N i t e l l a rise  into  deeper  t h e Ekman  from  1976, and r e d u c e d o f the deeper  examination  zone". exten-  t h e sudden water  Nitella  trans-  beds,  o f the macrophytes  obtained  t h e summer o f 1974/75 t h e e m e r g e n t s p e c i e s o f (Myriophyllum  the shallow l i t t o r a l  during  t h e r e was  samples.  a q u a t i c macrophytes  penetrated  the " N i t e l l a  water, b u t f o l l o w i n g  t h e r e was a d i e - o f f  During  in  sp. forming  i n January  w h i c h was a p p a r e n t in  down t o 17.5 m e t r e s d e p t h  summer o f 197 5/7 6 t h e r e was a g r a d u a l  i n lake l e v e l  parency,  39 -  s p . and P o t a m o g e t o n s p . ) ,  zone o f s h e l t e r e d  areas o f the lake,  t h e l a k e s u r f a c e and s u c c e s s f u l l y  flowered, but  t h e summers o f 1975/76 and 1976/77 t h e r i s i n g and  maintained  lake l e v e l s  d u r i n g summer p r e v e n t e d  successful  flowering o f these s p e c i e s .  LITTORAL  BENTHOS  Sampling  variability  The  v a r i a n c e t o mean r a t i o ,  w h i c h i s an i n d e x o f d i s p e r -  sion,  i s g r e a t e r t h a n one f o r t o t a l  total  insects  intervals  (Elliott val  and o l i g o c h a e t e s a t e a c h  sampled  tributions,  animals,  (Table I V ) .  total  of the three  T h i s suggests  molluscs, depth  contagious  dis-  w h i c h a r e usual- f o r most b e n t h i c i n v e r t e b r a t e s  1971).  f o r the t o t a l  However, o n l y a t t h e 11-12 m e t r e d e p t h molluscs i s this  a significant  inter-  departure  2 from  unity  ( a t p<0.05 X  Table)  indicating  that  the remainder  Table IV.  Sampling v a r i a b i l i t y w i t h i n the drawdown (at 5-6 m, 9th June  '76), and N i t e l l a  (at 2-3 m, 27th May  '76), mixed  (at 11-12 m, 29th March '76) zones  at Hautaruke Bay. n = 10 r e p l i c a t e s  a t each depth  interval.  Depth Interval (metres)  Mean Number  95% Confidence Limits  TOTAL ANIMALS  2-3 5-6 11 - 12  221 405 463  + 24 + 39 + 48  1532 3955 5886  6.9 9.8 12.7  TOTAL MOLLUSCS  2-3 5-6 11 - 12  71 126 266  + 12 + 9  ±  37 6 . 191 5660  5.3 1.5 21.3*  TOTAL INSECTS  2-3 5-6 11 - 12  75 244 130  + 16 + 32 + 17  663 2666 711  8.8 10. 9 5.5  OLIGOCHAETES  2-3 5-6 11 - 12  68 32 66  + 18 + 11 + 11  840 333 336  12. 4 10. 4 5.1  * = s i g n i f i c a n t departure from u n i t y  4 7  Variance •  (p<0.05 Table o f X )  Variance Mean  -  c o u l d be  randomly  41  -  distributed.  Some o f t h e p r o b l e m s a s s o c i a t e d w i t h s a m p l i n g invertebrates are  Northcote toral  and  v a r i a b i l i t y due  found  and  substrate within scale  cause  i t varies  invertebrates, be  this  the  and  depth  this  t o the wide  and  season.  sampler  lit-  variation  zone. in relation  to  i s an u n a v o i d a b l e p r o b l e m ,  so t h e c h o i c e o f q u a d r a t  Bay  Hautaruke  throughout  (Elliott  i n the upper  the  be-  taxa of benthic  size  1971).  is It  unlikely appears  N i t e l l a zone t h i s was  heterogeneity within  minimal.  The  the l i t t o r a l  the d i f f e r e n t and  Bay  inorganic  zone.  zones  s u b s t r a t e was  T h e r e was  little  t h e d e n s i t y o f m a c r o p h y t e g r o w t h was zones,  o c c u r r i n g w i t h depth  a  sampl-  uniform  gross  clumping drawdown  relatively  the g r e a t e s t v a r i a b i l i t y i n d e n s i t y  i n t h e N i t e l l a zone.  lake the shallow l i t t o r a l  geneity within  i n the  m a c r o p h y t e s p e c i e s i n t h e m i x e d and  homogeneous w i t h i n  the  quadrat  with t o t a l molluscs.  a r e a was  zones,  t o changes i n depth  c o n s i d e r a b l y between d i f f e r e n t  a t Hautaruke  At  to  to  equipment, h e t e r o g e n e i t y o f  attributed  appropriate f o r a l l taxa  problem  in relation  of contagious d i s t r i b u t i o n s  a r e a e n c l o s e d by  of  Among t h o s e r e l e v a n t  the g r e a t e s t v a r i a b i l i t y i n the shallow  (0 - 5 m . ) ,  The  ing  of sampling v a r i a b i l i t y  (1952).  o p e r a t i o n o f the sampling  substrate,  that  causes  study are contagious d i s t r i b u t i o n s  size,  to  and  d e s c r i b e d by N o r t h c o t e  this  in  i n lakes,  of benthic  the l i t t o r a l  areas  zone,  Although  throughout  showed t h e g r e a t e s t h e t e r o -  within  the sampling  area  this  -  42 -  was n o t s o . The p a p a free of  silt  s u b s t r a t e was i d e a l  from c o a r s e d e b r i s , which might  t h e jaws.  ideal  f o r Ekman s a m p l i n g a n d  interfere with  closing  The c h o i c e o f a 0.8 mm mesh was p e r h a p s n o t  f o r c h i r o n o m i d s and o l i g o c h a e t e s .  instars  and s m a l l  i n d i v i d u a l s would  washing  and s i e v i n g o f t h e s a m p l e s .  Many o f t h e i r  have been  lost  during  P o o l i n g o f t h e d a t a o v e r t h e t w e l v e month p e r i o d duces ing  s e a s o n a l changes  as a c a u s e o f v a r i a b i l i t y ,  the d a t a from d i f f e r e n t  d e p t h a s an a d d i t i o n a l fidence  limits  depths w i t h i n  zones  cause o f v a r i a b i l i t y .  on t h e means o f 10 r e p l i c a t e s  introduces  The 95% c o n t a k e n on t h e  t h a n c o u l d be e x p e c t e d i n t h e r e s u l t s  s a m p l i n g programme.  intro-  and p o o l -  same day and f r o m t h e same d e p t h g i v e an i n d i c a t i o n variability  early  of less  of the  - 43 -  Depth  distribution  The mean number of t o t a l animals f o r the twelve month 2 sampling p e r i o d i n the upperdrawdown zone i s l e s s than 1000/m (Figure 11) with an order of magnitude i n c r e a s e i n numbers 2 i n the lower drawdown zone  {cL 9 000/m ).  There i s l i t t l e  change i n mean numbers of t o t a l animals throughout the lower drawdown, mixed, and upper N i t e l l a zones  (1 - 10 metres), ...  but there i s a decrease i n numbers throughout the lower N i t e l l a zone to the s u b l i t t o r a l . o l i g o c h a e t e s account f o r i n v e r t e b r a t e fauna  Molluscs, insects,  > 9 5% o f the numbers of the macro-  (Figure 12).  I t i s the m o l l u s c s and  i n s e c t s which c o n t r i b u t e most t o produce the o v e r a l l of depth d i s t r i b u t i o n .  and  pattern  O l i g o c h a e t e s show a maximum d e n s i t y  at 1 - 3 metres depth, which,  i n the p r o f i l e o f t o t a l animals,  masks the s l i g h t l y reduced numbers of i n s e c t s and m o l l u s c s i n the lower drawdown zone  (JFigure 11) .  T O T A L  OLiq-OCHflETES  A N IM-ALS  o u  5000  NUMBER OF A N I M A L S pvt. S Q U A R E M E T R E  FIGURE 11. The depth d i s t r i b u t i o n of t o t a l animals, m o l l u s c s , i n s e c t s , and o l i g o c h a e t e s i n the l i t t o r a l zone at Hautaruke Bay. The mean number of i n d i v i d u a l s p e r Ekman sample from each metre depth i n t e r v a l d u r i n g the 12 month sampling p e r i o d , e x p r e s s e d as number of animals p e r square metre. (n.) = sample s i z e s .  -  45  -  Composition  Several  taxa,  which are prominent i n the  e r n Hemisphere temperate l a k e s a r e or r a r e in  New  (e.g.  Ephemeroptera, P l e c o p t e r a ,  Zealand  Lakes  (Marples  1962,  Lake d w e l l i n g P l e c o p t e r a as  are  truly  the w i n t e r flies  sp.)  proximity  emergence i n l a t e  in  the  In New  within  the  do  Zealand  i n L a k e Waikaremoana,  Chapman p e r s .  comm.) and  i n f l o w i n g s t r e a m s may O d o n a t a and  food.  However,  during  stream-dwelling stony  shores  may-  of  the  disappear  Amphipods,  after  although  c a t c h m e n t o f L a k e Waikaremoana, a r e were n o t  semi-terrestrial  i m p o r t a n c e i n New  the  s p r i n g / e a r l y summer.  damp l e a f  trout  of  Amphipoda)  1975).  o f s t r e a m mouths, b u t  common i n t h e  to  absent  North-  Chaoborinae)  Isopoda,  Forsyth  c o l o n i z e the  i n f l o w i n g s t r e a m s , and  The  (e.g.  l a k e - d w e l l i n g Ephemeroptera.  (Zephlebia  present  are  months nymphs o f one  l a k e i n the  absent  fauna of  litter the  found  species of  two  forest  i n the  o f Amphipoda floors  specimens found  have o r i g i n a t e d f r o m t h i s T r i c h o p t e r a are  Zealand  lake. are  (Dr. in  rare  M.A. the  source.  t h e r e f o r e o f much  lakes - p a r t i c u l a r l y with  greater  respect  -  46 -  SLm.lLmr\a.e.a.sp.  PhjjSa&thaSpFwu.sLa-SpG^tjK.<wiMS sp.  |  SPHAERIIDS  Hy'u.citjLipL. Sp-  M E T R E  s  Pycnocznihodes sp"T>upLui.uljLS sp  HYDROPTl LIT>S CERRTOPOqONlDS Pcui.ox<j£th.bia,3p. C H I R O N O M I D S  NEMERTERNS CYCLOPOID COPEPoDS  OSTRftCOBS HYDRACRRINA Oi CHYBpRIDS |  1  NEMATODES O L I C T O C H A E T E S  LEECHES  PLANARIANS  \  FIGURE 12. The c o m p o s i t i o n of the l i t t o r a l i n v e r t e b r a t e f a u n a a t Hautaruke Bay, Lake Waikaremoana, showing the mean number of i n d i v i d u a l s p e r square metre f o r each metre depth i n t e r v a l of the l i t t o r a l zone d u r i n g the 12 month s a m p l i n g p e r i o d .  -  Even those groups Zealand  lakes,  47 -  o f a n i m a l s , w h i c h a r e p r e s e n t i n New  show a r a t h e r  low s p e c i e s d i v e r s i t y .  the l i t t o r a l  species o f chironomids  are  6 s p e c i e s , b u t p r o b a b l y no more t h a n  at least  1975)  i n L a k e Waikaremoana t h e r e 10  (Forsyth  - compared w i t h some S c a n d i n a v i a n l a k e s e . g . L a k e A n k a r -  vattnet,  Sweden:  regulated age  Among  56 s p e c i e s o f l i t t o r a l  lake Blasjon:  reservoir  27 s p e c i e s  i n England:  chironomids,  (Grimas  1961),  and t h e  and a  57 s p e c i e s o f c h i r o n o m i d s  stor-  (Mundie  1957) . The of  greatest diversity  i n the l i t t o r a l  invertebrate  L a k e Waikaremoana o c c u r r e d i n t h e s h a l l o w l i t t o r a l .  ula  nitens,  and  at least  less  than The  rodes  ostracods, chydorids, planarians,  Nymph-  ceratopogonids  2 s p e c i e s o f c h i r o n o m i d s were o n l y f o u n d  7 metres  fauna  a t depths  (Figure 12).  s p h a e r i i d s and two s p e c i e s o f T r i c h o p t e r a ,  Pycnocent-  s p . and P a r o x y e t h i r a h e n d e r s o n i , o c c u r t h r o u g h o u t t h e  littoral,  b u t show maxima i n t h e drawdown a n d / o r  sublittoral  zones. The  other 2 species of Trichoptera,  chironomids  distribution  Physastra  s p . , a l l more o r l e s s  to the p r o f i l e of t o t a l  Two o f t h e l e s s Simlimnaea  total  and t h e two a b u n d a n t s p e c i e s o f g a s t r o p o d s ,  mopyrgus s p . and G y r a u l u s depth  t h e Odonata,  show a  Potasimilar  animals.  common g a s t r o p o d s , P h y s a s t r a s p . a n d  s p . , o c c u r w i t h i n more l o c a l i z e d  depth  zones.  s p . , w h i c h was more a b u n d a n t d u r i n g summer, o c c u r r e d  - 48  l a r g e l y i n the N i t e l l a  -  zone, and Simlimnaea sp. showed a max-  imum d e n s i t y i n the mixed and lower drawdown zones and  was  more abundant d u r i n g w i n t e r . Only a s i n g l e koura (.Paranephrops p l a n i f r o n s - the f r e s h water c r a y f i s h ) was  taken i n the Ekman samples; they are prob-  a b l y able to take e v a s i v e a c t i o n .  They were not i n f r e q u e n t l y  seen d u r i n g scuba surveys.  Seasonal Changes i n depth d i s t r i b u t i o n T o t a l animals The three s e r i e s o f samples taken d u r i n g May i n c l u s i v e were combined  t o August  to examine the p r o f i l e o f w i n t e r depth  d i s t r i b u t i o n , and the three s e r i e s o f samples taken d u r i n g November to February i n c l u s i v e were combined  to g i v e the summer  profile. For  s t a t i s t i c a l comparison between summer and w i n t e r depth  d i s t r i b u t i o n the l i t t o r a l  zone was d i v i d e d i n t o the upper and  lower drawdown zone, the mixed zone, and the upper and lower Nitella the  zone  (Figure 13).  Sample s i z e s were too s m a l l w i t h i n  upper drawdown and s u b l i t t o r a l zones to make v a l i d  istical  stat-  comparisons between w i n t e r and summer i n these depth  intervals. There i s l i t t l e d i f f e r e n c e i n the mean number of t o t a l animals w i t h i n the e n t i r e l i t t o r a l summer (6200/m  2  zone between w i n t e r and  2 i n w i n t e r , 6700/m t i n summer), but there are  t mean o f means from each 2 metre depth i n t e r v a l o f the a l zone.  littor-  -  49 -  T O T A L  (UPPER)  i •  D E 3 P T H 5  /315-  (5)  Z O N E (LOWER)  (0 M I X E D  M 7 E T R E II  (3)  ^RAwpqw_N_  Z O N E  S  A N I M A L S  (0  (0  (6)  (5)  (2-).  (3)  (3)  (3)  (4-)  (3)  (4-)  (3)  (UPPER)  " Z O N E (LOWER)  I7i SU6LITTOR.AU  (3)  (3)  11-  5 0 oo  NUMflER OF A N I M A L S /Oer SQUARE M E T R E W I N T E R  (MAY-Auq-USr  FIGURE 13.  LM.tLustve)  SUMMER (NOVEMBER-FEBRUARY  inclusive,)  S e a s o n a l changes i n the depth d i s t r i b u t i o n o f t o t a l a n i m a l s a t Hautaruke Bay.  (it) = sample s i z e s i n each 2 metre depth i n t e r v a l . % = s i g n i f i c a n t d i f f e r e n c e a t p < 0 . 0 5 K r u s k a l - W a l l i s Test between summer and w i n t e r i n the depth zones i n d i c a t e d by the v e r t i c a l b a r s .  -  significant  50 -  d i f f e r e n c e s between w i n t e r and summer i n the depth  distribution.  During w i n t e r the maximum d e n s i t y o f animals  occurs i n the lower drawdown and mixed zones w i t h  significantly  g r e a t e r numbers than o c c u r r e d i n the mixed zone d u r i n g summer (p<0.05 K r u s k a l W a l l i s T e s t ) . even d i s t r i b u t i o n  During summer t h e r e i s a more  o f animals throughout  a bulge i n numbers i n the N i t e l l a zone. of  animals  icantly  the l i t t o r a l  The i n c r e a s e d numbers  i n the N i t e l l a zone d u r i n g summer i s o n l y  g r e a t e r than w i n t e r  w i t h i n the lower N i t e l l a  zone, w i t h  signif-  (at p<0.05 K r u s k a l W a l l i s Test)  zone.  T o t a l m o l l u s c s , t o t a l i n s e c t s and o l i g o c h a e t e s There may be some o v e r a l l  i n c r e a s e i n the numbers o f t o t a l  m o l l u s c s w i t h i n the e n t i r e l i t t o r a l 2  mean o f 2850/m  zone d u r i n g summer from a 2  i n w i n t e r t o 3250/m  pears t o be l i t t l e  i n summer, but t h e r e ap-  d i f f e r e n c e between summer and w i n t e r i n the  numbers o f i n s e c t s and o l i g o c h a e t e s (Figure 14). these seasonal comparisons i n o v e r a l l  However,  numbers, where t h e r e are  seasonal changes i n depth d i s t r i b u t i o n ,  are not s t r i c t l y  valid,  because o f the uneven slope and c o n f i g u r a t i o n o f the l i t t o r a l (Figures 6 & 7). Both t o t a l m o l l u s c s and t o t a l i n s e c t s show maximum densities  i n the mixed zone d u r i n g w i n t e r , with a downward  d u r i n g summer.  T h i s downward  shift  s h i f t i s deeper i n m o l l u s c s ,  which show g r e a t e r numbers d u r i n g summer than w i n t e r  throughout  FIGURE 14. S e a s o n a l changes i n the d e p t h d i s t r i b u t i o n of m o l l u s c s , i n s e c t s and o l i g o c h a e t e s at Hautaruke Bay. A s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e ( a t p < 0,05, K r u s k a l - W a l l i s T e s t ) between summer and w i n t e r i n the depth zones i n d i c a t e d by the v e r t i c a l b a r s . (n.) = sample s i z e s .  -  the N i t e l l a in  zone, whereas  52 -  i n s e c t s show an i n c r e a s e  the upper, b u t n o t the lower, N i t e l l a T h e r e i s an i n c r e a s e  significant  summer, b u t t h e r e  d i f f e r e n c e between  summer  depth d i s t r i b u t i o n  ( a t p<0.05 K r u s k a l  S e a s o n a l changes -  Molluscs  The  gastropods,  Potamopyrgus  b o t h show t h e same s e a s o n a l the N i t e l l a  zone d u r i n g  mixed  zone d u r i n g w i n t e r  tween  summer  Kruskal mixed  and w i n t e r  W a l l i s Test)  zone d u r i n g  i n numbers o f o l i g o c h a e t e s  l o w e r drawdown zone d u r i n g ally  i n numbers  i n the  statistic-  and w i n t e r  i n the  Wallis Test).  a n t i p o d a r u m and G y r a u l u s s p . ,  patterns  summer,  i s no  summer.  of increased  numbers i n  and i n c r e a s e d numbers i n t h e  (Figure 15).  These d i f f e r e n c e s be-  are s t a t i s t i c a l l y  significant  i n the lower N i t e l l a  (p<0.05  zone and i n t h e  zone, and f o r G y r a u l u s s p . i n t h e l o w e r drawdown  zone  also. The  bivalves show a d i f f e r e n t  seasonal  pattern.  They  a more o r l e s s  even d i s t r i b u t i o n  throughout the l i t t o r a l  during winter,  but during  they  summer  ferences  are not s t a t i s t i c a l l y  S e a s o n a l changes - Odonata The grayi  Nitella  two s p e c i e s  and  o f Odonata  and t h e d a m s e l f l y  zone  show an i n c r e a s e i n  numbers i n t h e l o w e r drawdown and s u b l i t t o r a l d e c r e a s e i n t h e mixed•and  have  zones.  z o n e s , and a  These s e a s o n a l  dif-  significant.  Lepidoptera - the dragonfly  Xanthocnemis  Procordulia  z e a l a n d i c a - show  little  q  -  A  S  T  K  O  P  O  D  B / V A L V E S  S  LO  W I N T E R  o  i  S U M M E R  W I N T E R  S U M M E R  VJINTER  S U M M E R  3000  N U M B E R O F ANIMALS />e* S Q U A R E M E T R E  FIGURE 15. S e a s o n a l changes i n t h e d e p t h d i s t r i b u t i o n o f gastropods and b i v a l v e s a t Hautaruke Bay. A s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e ( a t p < 0.05, K r u s k a l - W a l l i s T e s t ) between summer and w i n t e r i n the d e p t h zones i n d i c a t e d by the v e r t i c a l b a r s .  -  difference size  i n total  54 -  numbers between summer and w i n t e r .  frequency d i s t r i b u t i o n s of the larvae  p e r i o d o f emergence o f t h e a d u l t s of  the f i n a l  decline This  instar,  i s not such a  i n numbers f o l l o w i n g emergence o f t h e a d u l t s  imum d e n s i t y  the winter  o f P. g r a y i d u r i n g  i n t h e maximum  months  (Figure 16).  winter  occurs  drawdown z o n e , w h e r e a s t h e maximum d e n s i t y winter  The close  occurs  females d e p o s i t  1-2 months t o h a t c h were f o u n d w i d e l y  The  during  t h e stems o r l e a v e s  Early instar  throughout the l i t t o r a l  summer  summer  larzone  (February). deposit  o f emergent macrophytes  The e a r l y i n s t a r  m e t r e s d e p t h by l a t e  of the  t o t h e b o t t o m and  (Armstrong 1958).  dispersed  female.  November t o J a n u a r y .  a d u l t d a m s e l f l i e s , X. z e a l a n d i c a ,  & Cowley 1966). 19  zone.  behaviour,  s i n g l e eggs a t t h e s u r f a c e  below 2 metres d e p t h by l a t e  on  zealandica  i n t r u d i n g m a l e s and s e i z i n g any p a s s i n g  w a t e r o v e r t h e l i t t o r a l zone, w h i c h s i n k  vae  o f X.  d e e p e r t h a n P. g r a y i - i n , t h e m i x e d  O v i p o s i t i n g b y P. g r a y i o c c u r s  take  The max-  i n t h e lower  t o t h e w a t e r ' s edge, and e x h i b i t t e r r i t o r i a l  adult  densit-  a d u l t male d r a g o n f l i e s , P. g r a y i , t a k e up s t a t i o n  clashing with  The  i n summer.  (Macan 1977, P e n d e r g a s t &  shown an upward s h i f t  o f larvae during  during  great  1966).  Both s p e c i e s ies  t a k e more t h a n one y e a r t o  and h e n c e t h e r e  i s n o t u n u s u a l i n Odonata  Cowley  f o l l o w i n g the,,  i n summer s u g g e s t s t h a t many  t h e l a r v a e o f t h e s e two s p e c i e s  reach  The  their  eggs  (Pendergast  l a r v a e were f o u n d down t o  (January),  but the greatest  O D O N A T A  LEPIDO  P T ER A  cn  W I N T E R  S U M M E R  W I N T E R  S U M M E R  W I N T E R  S U M M E R  O 5oo i i — i i—t i NUMBER OF A N I M A L S  piK S q f f l R E  METRE  FIGURE 16. S e a s o n a l changes i n t h e depth d i s t r i b u t i o n of Odonata and L e p i d o p t e r a a t Hautaruke Bay. A s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e ( a t p < 0 . 0 5 , K r u s k a l - W a l l i s T e s t ) between summer and w i n t e r i n t h e depth zones i n d i c a t e d by the v e r t i c a l b a r s .  - 56 -  numbers o c c u r r e d between 5 and 10 metres  depth.  The a q u a t i c l a r v a e of the s m a l l moth, Nymphula n i t e n s , take a s i n g l e year to complete  their l i f e  c o n f i n e d t o the shallow l i t t o r a l ,  cycle.  They are  and t h e i r numbers are temp-  o r a r i l y reduced f o l l o w i n g emergence o f the a d u l t s i n summer (Figure 16).  Seasonal changes - T r i c h o p t e r a The l a r g e c a d d i s , T r i p l e c t i d e s sp., which takes a s i n g l e year to complete  i t slife  c y c l e , shows a decrease i n numbers  i n a l l zones d u r i n g the summer months f o l l o w i n g emergence of the  adults  macrophytes  (Figure 17).  Pupae were found a t t a c h e d t o a q u a t i c  d u r i n g December, January and February a t depths  r a n g i n g from 1 t o 14 metres, w i t h a maximum a t 5 metres  depth.  The s m a l l sandgrain-cased c a d d i s , Pycnocentrodes sp., shows no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e i n numbers or depth d i s t r i b u t i o n between summer and w i n t e r , although the g r e a t e s t numbers were found i n the drawdown and lower N i t e l l a zones w i t h a p a u c i t y , p a r t i c u l a r l y d u r i n g summer, i n the midlittoral.  Pupae were not found d u r i n g Ekman sampling.  The f i n d i n g o f the pupae (attached t o a q u a t i c  macrophytes)  throughout the year suggests t h a t the s m a l l h y d r o p t i l i d s , P a r o x y e t h i r a t i l l y a r d i and P a r o x y e t h i r a hendersoni, pass through a t l e a s t 2 g e n e r a t i o n s i n a year.  The w i n t e r genera-  t i o n of P. t i l l y a r d i i s c o n c e n t r a t e d mainly i n the mixed and lower drawdown zones with a maximum number o f pupae found i n  T  R  PijcnjOpeM-btodzs  I  C  H  O  P  T  E  R  A  sp-  P.  kje.ndexsonL  Ul  W I N T E R  S U M M E R  WINTER SUMMER  WINTER  S U M M E R  WINTER SUMMER  500  N U M B E R OF A N I M A L S pen SQUARE M E T R E FIGURE  17. Seasonal changes i n the depth d i s t r i b u t i o n of T r i c h o p t e r a a t Hautaruke Bay. A s t e r i s k i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e ( a t p < 0.05, K r u s k a l - W a l l i s T e s t ) between summer and w i n t e r i n the depth zones i n d i c a t e d by the v e r t i c a l b a r s .  -  October  58 -  a t 4 - 6 metres depth.  centrated mainly pupae o c c u r r i n g There  i n the N i t e l l a i n January  zone w i t h maximum numbers o f  between 9 t o 15 m e t r e s  i s no s t a t i s t i c a l l y  numbers o r d e p t h  The summer g e n e r a t i o n i s c o n -  distribution  significant  depth.  difference  i nthe  o f P. h e n d e r s o n i between  and w i n t e r , a l t h o u g h t h e g r e a t e s t numbers were f o u n d  summer  i n the  drawdown zone i n w i n t e r , and i n t h e s u b l i t t o r a l i n summer, with  a p a u c i t y o f numbers i n t h e m i d - l i t t o r a l .  found a t depths  r a n g i n g from  S e a s o n a l changes There  i s a s l i g h t downward s h i f t  o f Chironominae  only  statistically  or  i n the depth  significant  Tanypodinae  difference  i s a g r e a t e r number  zone d u r i n g w i n t e r  (Figure 18).  show no s i g n i f i c a n t  difference  depth  distribution  between summer and w i n t e r .  The  unidentified  group  of chironomids  include  species with r e p r e s e n t a t i v e s of the Orthocladinae. an o v e r a l l  decrease  statistically  distribu-  i n summer compared w i t h w i n t e r , b u t t h e  the lower N i t e l l a The  metres.  chironomids  tion  in  1 to 20  Pupae were  i n numbers  at least  4  There i s  i n numbers d u r i n g summer, b u t t h i s  i s not  significant.  TROUT Composition The  o f the t o t a l  size,  catch of trout  catch  m a t u r i t y and s p e c i e s c o m p o s i t i o n o f t h e t o t a l i n t h e g i l l n e t s d u r i n g t h e p e r i o d F e b r u a r y 1976  C H I R O N O M I D S  W I N T E R O (a  SUMMER  WINTER.  SUMMER  zooo I  I  N U M B E R O F A N I M A L S pvi S Q U A R E M E T R E  FIGURE 18. S e a s o n a l changes i n t h e depth d i s t r i b u t i o n of chironomids a t Hautaruke Bay. A s t e r i s k indicates a s i g n i f i c a n t difference (at p < 0 . 0 5 , Kruskal-Wallis Test) between summer and w i n t e r i n t h e depth zones i n d i c a t e d by t h e v e r t i c a l b a r s .  WINTER SUMMER  - 60 -  to  December 1976  inclusive  (Figure 19)  shows t h a t 82% of  t o t a l c a t c h were rainbow t r o u t ; 18% were brown t r o u t .  the  80%  of  the rainbow t r o u t were immature whereas only 53% of the brown t r o u t were immature.  The mature brown t r o u t have a  c a n t l y g r e a t e r mean l e n g t h  (56.5  cms. , 95% C L .  the mature rainbow t r o u t (mean l e n g t h 51.8  cms  signifi-  + 1.4) , 95%  than  CL.  +  0.9) .  Spatial  distribution  The  l e n g t h frequency  drawdown, deep l i t t o r a l 20.  Considering  d i s t r i b u t i o n s of t r o u t caught i n the  and  l i m n e t i c nets are shown i n F i g u r e  f i r s t the rainbow t r o u t : - i n the drawdown  zone the c a t c h c o n s i s t e d of small j u v e n i l e s (< 26 cms.) l a r g e , mostly mature, f i s h , intermediate-sized f i s h .  with o n l y a s m a l l p r o p o r t i o n of  In the l i m n e t i c zone the c a t c h con-  s i s t e d l a r g e l y of i n t e r m e d i a t e - s i z e d j u v e n i l e s . deep l i t t o r a l  zone the c a t c h shows a bimodal  Over the  length-frequency  d i s t r i b u t i o n of i n t e r m e d i a t e - s i z e d j u v e n i l e s , very few juveniles fish.  (.< 26 cms  ), and  and  small  a group of l a r g e r , mostly mature  There i s no s i g n i f i c a n t d i f f e r e n c e i n s i z e between the  mature rainbow t r o u t caught i n the deep l i t t o r a l  and  i n the  drawdown zones. The littoral,  d i s t r i b u t i o n of brown t r o u t i n the l i m n e t i c , deep and drawdown nets shows a s i m i l a r , but l e s s  d e f i n e d , p a t t e r n a c c o r d i n g to s i z e and m a t u r i t y  (N.B.  clearly smaller  sample s i z e s ) , but i n a d d i t i o n there i s a s i g n i f i c a n t d i f f e r e n c e  -  61  LENGTH F I G U R E  -  CMS-  19. The c o m p o s i t i o n of the t o t a l c a t c h of t r o u t i n the g i l l n e t s (February 1976 - December 1976) from b o t h s t a t i o n s , a c c o r d i n g t o s p e c i e s , s i z e and maturity. (rv) = sample s i z e s .  RAINBOW  TROUT  BROWN  '5-1  TROUT  20  LIMNETI  C  (33) 10  30  DEEP  3£j_ 38  ( i 50  5Jf  58  t i  U  LITTORAL  (ZO) 10 to  llf.  \i  ZL  Zi  30  31*  38  42.  4t  50  5^.  S"S  30  34-  38  L2.  4i  50  54-  58  '5i DRAWDOWN ZONE  10-i  7 to  (78)  DRAWDOWN ZONE  (*0  5 H  FIGURE 20. The p e r c e n t a g e l e n g t h c o m p o s i t i o n i n 2 cm. groupings of t r o u t caught i n g i l l n e t s i n the drawdown zone, i n the deep l i t t o r a l zone and i n the l i m n e t i c zone, from both s t a t i o n s ( F e b r u a r y 1976 December 1976 i n c l u s i v e ) . Immature f i s h ( b l a c k ) ; mature f i s h ( c r o s s - h a t c h e d ) . (^) = sample s i z e s  -  in  63  s i z e between t h e m a t u r e brown t r o u t  toral  and  i n t h e drawdown z o n e s .  brown t r o u t nificantly  caught  Wallis  Test).  zone,  egorized 1.  food items  mean l e n g t h o f m a t u r e 57.5  cms. , i s s i g -  55.1  cms  trout  (p<0.01 K r u s k a l  r e c o r d e d d u r i n g s t o m a c h a n a l y s i s were  cat-  as: L i m n e t i c food, which c o n s i s t e d  smelt,  larval  bullies  Cand an  by volume o f c h i r o n o m i d p u p a e ) ,  o f Daphnia  insignificant  carinata, quantity  a l l of which are s m a l l  (<3  cms  length). 2.  Littoral  food, which c o n s i s t e d of l i t t o r a l  brates ranging i n size and k o u r a up  lit-  analysis  The  larval  i n t h e deep  g r e a t e r t h a n t h e mean l e n g t h o f m a t u r e brown  i n t h e deep l i t t o r a l  Stomach  The  caught  i n t h e drawdown zone,  caught  in  -  cms-  a l o n g w i t h an Subadult  w h i c h may  adult  smelt, t r e a t e d  a l t h o u g h t h e y were o b s e r v e d  littoral  areas  from October  in  Taupo and  behaviour  Rotorua  and f e e d i n g .  ,  up  t o <=: 10  shoots  of  incident-  item.  gory, because,  Lakes  the  o n l y have been t a k e n  i n v e r t e b r a t e prey and  trout,  cms  planifrons)  adult b u l l i e s  i n the case o f rainbow  a q u a t i c macrophytes,  3.  Paranephrops  l e n g t h , s u b a d u l t and  l e n g t h , and  ally  t o d r a g o n f l y l a r v a e o f =^2.5  (the f r e s h w a t e r c r a y f i s h ,  t o c± 12  cms  up  inverte-  to A p r i l , they remain  Jolly  as a s e p a r a t e c a t e i n s c h o o l s i n the (19671 f o u n d  partially  pelagic  that in  -  64 -  4.  T e r r e s t r i a l i n s e c t s - l a r g e l y C o l e o p t e r a and  5.  Frogs - Hyla aurea.  6.  Debris - other than a q u a t i c macrophytes.  cicadas.  The s m a l l e r j u v e n i l e rainbow t r o u t c o n t a i n e d l a r g e l y limnetic  food i n t h e i r stomachs  (Figure  2 1 ) , and Daphnia were  an important food item p a r t i c u l a r l y d u r i n g s p r i n g summer.  Daphnia were found i n the stomachs of immature rainbow  t r o u t of up to 54 cms, length, the  and e a r l y  but Daphnia were not found i n  stomachs of any brown t r o u t . T e r r e s t r i a l insects  formed a s i g n i f i c a n t component o f the  d i e t o f rainbow t r o u t d u r i n g summer (November t o February i n c l u s i v e ) , and, o v e r a l l , formed 10 - 20% of t h e i r d i e t , but they c o n t r i b u t e d  i n s i g n i f i c a n t l y t o the d i e t of brown t r o u t .  Rainbow t r o u t contained an i n c r e a s i n g i n t h e i r stomachs w i t h i n c r e a s i n g formed a n e g l i g i b l e p r o p o r t i o n  amount o f d e b r i s  age and s i z e , but d e b r i s  o f the stomach contents o f  brown t r o u t . Subadult and a d u l t  smelt were an important food item f o r  both rainbow and brown t r o u t .  They formed an i n c r e a s i n g  p o r t i o n o f the d i e t of rainbow t r o u t w i t h i n c r e a s i n g s i z e , but they formed an even g r e a t e r p r o p o r t i o n  pro-  age and  of the d i e t  of brown t r o u t ; 50--. 70% i n the immature brown t r o u t , and 30 4 0% i n the p r e v i o u s spawner brown t r o u t , i n which b u l l i e s became the most important food item. piscivorous  than rainbow t r o u t .  Brown t r o u t were more  R A I N B O W I  I M  M A T U R  E  I+- !  T R O U T F  1+  ;s  3  H | PREVIOUS  2+  R 0 WN  TR O U T  I I M M A T U R E FISH I F ' " S T V £ « R SecONJ) Y E A R  SPAWNERS  //V  L A K E  //V  LIMNETIC  FOOD  LITTORAL  FOOP  PREV/OUS SPA WAVERS  L A K E  u  L I TTOR.AL FOOD  i • I SMELT (POSTLARVAL)  (poSTLARVAu)  23  1 TERRESTRIAL. INSECTS  I  DEBRIS  FIGURE 21. The c o m p o s i t i o n  TERRESTRIAL  INSECTS  L  of the d i e t s of brown and rainbow t r o u t i n Lake Waikaremoana. (February 1976 - December 1976).  -  F r o g s were o n l y f o u n d (..> 55 cms The  66  i n the  only l i t t o r a l  invertebrate,  by volume o r o c c u r r e n c e  was  late  instar  Rainbow t r o u t brates;  were an  early  instar  inclusive.  which c o n t r i b u t e d s i g n i f -  to the d i e t  late  o f brown  trout,  i n any  larvae,  Xanthocnemis  t i o n by  occurrence, but  of l i t t o r a l  instar  l a r v a e as w e l l .  item i n the d i e t  found  trout  l a r v a e of the d r a g o n f l y , P r o c o r d u l i a g r a y i .  f e d upon t h e  important  b u t were n o t  January  contained a greater variety  they a l s o  but took  s t o m a c h s o f l a r g e brown  l e n g t h ) between November and  icantly the  -  l a r v a e o f P.  Triplectides  of larger  brown t r o u t  inverte-  larvae  rainbow  stomachs.  trout,  Damselfly  z e a l a n d i c a , formed a s i g n i f i c a n t n o t volume, i n t h e d i e t  grayi,  of  propor-  rainbow  trout. There  was  an  i n c r e a s i n g percentage  a decreasing percentage c r e a s i n g age  and  The  food  limnetic Seasonal  larval size  size  size  i n b o t h brown t r o u t  larval bullies,  o f the l a r v a l  fish  and  up  o f 25 During  and  rainbow  to d  trout.  o r more o f t h e s e p r e y  19 mms  - 30 mms  l e n g t h , and by  carinata,  s e a s o n a l changes i n the  a r e shown i n F i g u r e 22.  t h e y a r e a l l s m a l l ; D a p h n i a up  bullies  and  food, i n the d i e t with i n -  c h a n g e s i n t h e abundance o f D a p h n i a  s m e l t and  food,  resources  much o f t h e y e a r one but  of limnetic  of l i t t o r a l  t o 4 mms larval  Throughout  items  i s abundant,  length, smelt  larval  reaching a  late winter/early spring.  the p e r i o d October  t o December 1976  inclusive,  - 67 -  30 L  Z5  E  10  <T T H  IS  ::  i  I  N  I  10  vnmS.  50-  L A R V A L FISH |Aufr  |SEPT  | Q C T  I  N O V  | D E C  T « N  IFEB  /<?77  (W-l-r)  IM U M  5  5  |MAR  (Sttx)  [HPR I MAY |TUN |TUL |  LARVAL  SMELT  4q 30  B  E A  O F | Auq- [SEPT  I OCT  |N O V  I DEC  |TA N |F E B  ) M A R | fl P R  |MAY  | J U N |J u L  I N D  ("Ix)  I V  LARVAL BULLIES  /  D 1/ A L S  P £ R  40  20  l — |l DEC  3  A up |s£>r | oc*r~| NOV  Q Ll fl  | J~AN | FE B | MAR |BPR  |MA» | JUN | J U C  R E M E T ft £  LAPHNIA  10,000  cL)  /O/JOO  i AUG|SEPT|ocr | NO v [DEC I TAN | FE 8 | M AR | APPT| MAY*TUNT  FIGURE 22. Seasonal changes i n a) the s i z e of l a r v a l smelt (•) and l a r v a l b u l l i e s ( ° ) , and i n the numbers of b) l a r v a l smelt c) l a r v a l b u l l i e s & d) Daphnia c a r i n a t a (August 1976 - J u l y 1977). Circles are the mean of 4 samples per month (2 from each s t a t i o n ) and the v e r t i c a l bars r e p r e s e n t 957. c o n f i d e n c e l i m i t s .  -  when e i t h e r numbers o r s i z e partially  filled  Terrestrial festiva,  68 -  of larval  t h e gap i n t h i s  insects,  f i s h were low, D a p h n i a  supply  particularly  of limnetic  t h e Manuka b e e t l e ,  were a l s o b e c o m i n g i n c r e a s i n g l y  lake surface a t t h i s  available  F e b r u a r y / M a r c h 19 77 and the- o t h e r  Recruitment  rainbow t r o u t  streams mostly  fish,  entered  the l a k e from the n u r s e r y  a s autumn i m m i g r a n t s o r s p r i n g i m m i g r a n t s .  zone.in A p r i l  marks up t o t h e t i m e recent entry  of capture  i n t h e drawdown  devastating flood  had  a significant  ile  trout  t r o u t caught  effect  i n the g i l l n e t s ,  streams.  Few  Year  on t h e l e v e l  suggesting  1975/76  or August. undoubtedly  of recruitment  to the l a k e d u r i n g the subsequent year.  o f juven-r  The  s t r e a m s i n t h e n o r t h e a s t c o r n e r o f t h e c a t c h m e n t were of f i s h  recovered  their  trout entered The  f o l l o w i n g the f l o o d , i n v e r t e b r a t e fauna,  streams r e v e a l e d the presence CO + f r y ) .  but the streams  spawning completely  rapidly  and t h e s p a w n i n g r u n s o f  t h e s t r e a m s as u s u a l d u r i n g t h e w i n t e r  following spring electrofishing  parr  small juveniles  zone i n F e b r u a r y  o f New  A  i n t h e ......  and O c t o b e r h a d r e t a i n e d t h e i r  from the n u r s e r y  were c a p t u r e d  devoid  one  i n June 197 7.  high p r o p o r t i o n o f the small j u v e n i l e  The  a t the  o f j u v e n i l e s to the lake  Juvenile  drawdown  Pyronota  time.  T h e r e were two p e a k s i n t h e numbers o f l a r v a l in  food.  o f one o f t h e s e  of a s i n g l e year  T h e i r g r o w t h and s e a s o n a l  o f 1976. spawning  class of trout  timing of emigration  -  69 -  from the stream was f o l l o w e d by e l e c t r o f i s h i n g a t 1-2 monthly i n t e r v a l s , and i t was e s t a b l i s h e d t h a t the bulk o f the autumn immigrants  t o the lake were the f a s t e r - g r o w i n g 0 + j u v e n i l e s .  The slower growing  0 + j u v e n i l e s overwinter i n the stream and  form the bulk o f the s p r i n g immigrants  as 1 + j u v e n i l e s ,  (Fig-  ure 23) . T h i s produces  a bimodal l e n g t h frequency d i s t r i b u t i o n i n  the 1 + j u v e n i l e s d u r i n g t h e i r f i r s t  year i n the lake (see  February 1976, and October and December 1976, F i g u r e 2 3 ) , but by the end o f t h e i r second year they merge t o form a s i n g l e size-class.  Condition  factor  The s m a l l j u v e n i l e rainbow  t r o u t have a h i g h mean c o n d i -  t i o n f a c t o r when l e a v i n g the nursery streams, but d u r i n g t h e i r first  2-4 months i n the l a k e , when they were i n h a b i t i n g the  drawdown zone, there was a s i g n i f i c a n t drop i n t h e i r mean condition factor  (Figure 2 4 ) .  When they moved out i n t o the  l i m n e t i c zone (at a s i z e o f approximately 26 cms, length) the mean c o n d i t i o n f a c t o r i n c r e a s e d and remained  high u n t i l  they  reached a s i z e o f approximately 3 8 cms. and then t h e r e was a gradual f a l l i n the mean c o n d i t i o n f a c t o r with i n c r e a s i n g In  "previous spawner" rainbow  t r o u t the mean c o n d i t i o n  was s i g n i f i c a n t l y lower than i n immature rainbow comparable  size.  size.  factor  t r o u t of a  -  70  P R E V I O U S S P A W N E R.S  N U  M  6 E A  O F  F I S H  FIGURE 23. Length f r e q u e n c y d i s t r i b u t i o n s of rainbow t r o u t caught i n nets d u r i n g each 2 monthly s a m p l i n g . ^ = no n e t s s e t i n drawdown zone. T r o u t which e n t e r e d the l a k e as j u v e n i l e immigrants i n autumn = A, i n s p r i n g = S • = immature f i s h w i t h r i p e n i n g gonads.  52 50  C O N D I T I O N F  A  4s J  >(37)  >(37)  4^  • (to)  f(Zl)  44  T  42-  C T  4.0-  R  38-  (4)  O i  36 -|  5(zo)  % 3230-  /g-02(- ? c  22.-0Z5<?  26-03o-o34.0_<\.<\ 33-? 37-? L£Nq-T"H cms  38-0^'-f  4i-o45-<?  4.6.0\<?.<?  5b-o53-7  FIGURE 24. The mean c o n d i t i o n f a c t o r of rainbow trout i n r e l a t i o n t o s i z e and maturity (February 1976 - December 1976). (n.) = sample s i z e s . V e r t i c a l bars represent 95% confidence l i m i t s © =immature f i s h X =previous spawners  54.-057?  - 72  -  A f t e r the small j u v e n i l e rainbow t r o u t moved out i n t o the l i m n e t i c zone t h e i r growth r a t e was approximately  44 cms.  There was  r a p i d up t o a s i z e of  an i n c r e a s e i n modal l e n g t h  of ^ 3 cms /month i n the 1 + s p r i n g immigrant j u v e n i l e s between February 1976 and June 1976, (Figure 23).  Above a 44 eras, the  growth r a t e slowed down. Approximately h a l f o f the rainbow t r o u t matured a t 2 . • years o l d ; the remainder c o n t i n u i n g as immature f i s h i n t o t h e i r t h i r d year are subjecte d to i n t e n s e a n g l i n g pressure i n October and November, which d e p l e t e s the numbers of rainbow t r o u t maturing a t 3 years o l d . A f t e r reaching maturity  there i s l i t t l e  l e n g t h i n rainbow t r o u t , and with the f a l l very l i t t l e  i n c r e a s e i n weight.  increase i n  i n condition factor,  -  73  -  DISCUSSION  Before virtually t h a n any  h y d r o e l e c t r i c d e v e l o p m e n t L a k e Waikaremoana  a stabilized of  the  reservoirs. with  now  " r e s e r v o i r " o f much g r e a t e r  T h e r e were n a t u r a l f l u c t u a t i o n s i n l a k e  due  were i n e f f e c t  to the  the  similar  metres.  196 3 ) .  lowering  of those  lakes of  (McMynn and  (Campbell  initial  reverse  impoundment o f t h e B.C.  2.5  level  morphometric changes f o l l o w i n g h y d r o e l e c t r i c  ment i n 1946,  the  lake  periodicity,  level  i f not  the  develop-  lake  before  level, and  Campbell R i v e r drainage  L a r k i n 1 9 5 3 ) , and  However, t h e  of  described  Loch Garry,  continuing  i n that hydroelectric u t i l i z a t i o n  a regime o f  age  more f a m i l i a r man-made h y d r o e l e c t r i c r i v e r  a mean a n n u a l a m p l i t u d e o f The  in  river  was  be  lakes  f l u c t u a t i o n s , which i s u n n a t u r a l  i n amplitude  as  area  Scotland  i m p a c t s may o f the  after  more  imposes in  well.  MORPHOMETRIC CHANGES The  most s i g n i f i c a n t m o r p h o m e t r i c c h a n g e s i n L a k e Waik-  aremoana a r e reaches of  those  portionately  toral  the  streams e n t e r i n g the  The c± 17%  will  affecting  reduction  great  l o s s of  have r e d u c e d t h e zone o f  the  i n the  littoral  and  the  lower  lake. littoral  shallow  a similar,  magnitude thus d i m i n i s h i n g b o t h the  area,  littoral  potential total  l a k e by  area  with  a dispro-  (.< 5 m e t r e s deep) ,  production  of the  i f not  greater,  littoral  living  lit-  degree space  of  and  -  the  littoral  extent The on  food  than the  reduction  dependence o f the  are  i n the  makes t h e  resources  o f the  year,  small  area  of  total  the  being and  under the  influence of  L a r k i n 195 3 ) .  reaches during  these  The  to inundation  o f the  eggs i n e a r l y s p r i n g . and  g r a v e l s o f the  rising  reduce the  lake The  and  re-  zone a  limiting  for trout. streams a c c e s s i b l e been i n c r e a s e d  of questionable  when l a k e  liable  siltation  lake  level  life  zone,  by  value  -  f l u c t u a t i o n s (McMynn  r e d d s o f t r o u t spawning i n the  late winter, by  of t h e i r  littoral  l a k e has  are  lake  loss) .  transient periods),  length of t r i b u t a r y  creation of gauntlets,  ( d 4%  littoral  short,  the  spawning runs o f t r o u t from the  greater  when l i m n e t i c f o o d  c a r r y i n g c a p a c i t y of the  A l t h o u g h the  to  l i m n e t i c area  (fortunately only  relatively  i n the  t r o u t to a f a r  t r o u t at c e r t a i n stages  food  scarce  -  f o r the  c e r t a i n seasons o f the  sources  factor  the  space and/or  during  to  resources  74  levels  levels  are  during  low,  lower are  incubation  s l u g g i s h flow w i l l  predispose  p e r c o l a t i o n of water through  the  redds.  LAKE LEVEL FLUCTUATIONS Seasonal  periodicity  E v e n t h o u g h t h e r e may seasonal  periodicity  t e m p e r a t e and electric tern  be  considerable  of natural  (unregulated)  subarctic climates  development they  are  r e l a t e d t o summer s t o r a g e  differences in  (Figure 25),  likely  lakes  between  f o l l o w i n g hydro-  to f o l l o w a s i m i l a r  o f w a t e r and  the  maximum power  patgen-  -  75  a  LAKE  -)  BLASTON  M £ T R £ LOCH  S  L O M O N L  c  LflKE.WfllKflREMOflNfl ° Va^lio'ii'/a.'  / 'a ' 3 U ' s  1  1  1 8 1 110' 11 '/a] 1 z ' 3 I -V5'fe' 1  1  1  M O N T H S  FIGURE 25. Seasonal p e r i o d i c i t y of n a t u r a l f l u c t u a t i o n s i n lake l e v e l a) Lake B l a s j o n , s u b a r c t i c Sweden (Grimas 1961) b) Loch Lomond, S c o t l a n d ( a f t e r S l a c k 1957) c ) Lake Waikaremoana (a & b from E l d e r 1975)  - 76 -  e r a t i o n d u r i n g winter or accentuate, and  (Figure 26).  T h i s w i l l tend t o produce  a r i s i n g and maintained lake l e v e l i n summer,  a f a l l i n g lake l e v e l i n winter. T h i s r e g u l a t e d p a t t e r n i s c l o s e r to the n a t u r a l p e r i o d -  i c i t y o f lake l e v e l f l u c t u a t i o n s i n a r c t i c or c o n t i n e n t a l c l i m a t e s , where winter fall,  p r e c i p i t a t i o n i s i n the form o f snow-  and f r e e z i n g temperatures delay the r u n o f f to the l a k e s  u n t i l the s p r i n g thaw.  The delayed  r u n o f f may be prolonged  i n t o summer i n high a l p i n e and g l a c i a l melt catchments (e.g. L i l l o o e t Lake, B.C.). The  n a t u r a l f l u c t u a t i o n s i n lake l e v e l i n Lake B i a s j o n  f o l l o w i n g the s p r i n g r u n o f f show a s i m i l a r summer p a t t e r n t o the n a t u r a l f l u c t u a t i o n s i n Lake Waikaremoana - i . e . a high lake l e v e l i n e a r l y summer and f a l l i n g through l a t e summer. The  major d i f f e r e n c e between the n a t u r a l f l u c t u a t i o n s i n  these two lakes i s i n t h e i r winter  l e v e l s - f a l l i n g i n Lake  B l a s j o n ; r i s i n g i n Lake Waikaremoana. The major change i n the seasonal  p e r i o d i c i t y i n Lake  B l a s j o n f o l l o w i n g h y d r o e l e c t r i c development i s due t o summer storage m a i n t a i n i n g  a high l e v e l throughout the summer, a l -  though t h i s i s perhaps overshadowed by the e x t e n s i v e i n amplitude  increase  (Figure 26). In Lake Waikaremoana the seasonal  p e r i o d i c i t y has been t o t a l l y r e v e r s e d development, with l i t t l e  following hydroelectric  change i n amplitude.  43fci 435M  434'  E T R  433-  E  s  432431 43o-  (,14 -  (,13 M E  &I2. -  T  R E  til -  S Cio Gof 6og -  IT32.  I  1933  | / ? 3 4  FIGURE 26. The n a t u r a l and r e g u l a t e d l a k e l e v e l f l u c t u a t i o n s i n Lake B l a s j o n ( a f t e r Grimas 1961) and i n Lake Waikaremoana. The shaded areas r e p r e s e n t the e x t e n t of submergence of the weed beds d u r i n g summer. S = summer; W = w i n t e r .  -  Effects  on l i g h t  penetration  Quennerstedt fluctuations discusses  78 -  and p r i m a r y  C1958) d e s c r i b e s  on l a k e v e g e t a t i o n  producers  the effects  o f water  i n Scandinavian  t h e e f f e c t s o f summer s t o r a g e .  l a k e s , and  The p r o l o n g e d  submergence o f t h e a q u a t i c m a c r o p h y t e b e d s d u r i n g e t a t i o n a l p e r i o d p r o d u c e s an upward d i s p l a c e m e n t boundary o f r o o t e d a rising  lake  transparency Grimas due  (1962) d e s c r i b e s  effect will  a reduction  t o shore e r o s i o n i n Lake B l a s j o n  level  fluctuations.  o f t h e papa s h o r e s  the  accompanies a r i s i n g  level  during  and wave a c t i o n work upon t h i s  summer s t o r m s t h e r e transparency  level  transparency water  i n the l i t t o r a l more p r o l o n g e d  due  to wind-induced e p i l i m n i a l  out i n t o the lake i n Following  s p r i n g and on w a t e r  exposed papa  shores,  throughout t h e whole  currents.  t h e exposed papa has t h e t e x t u r e  wave a c t i o n p r o d u c e s r e l a t i v e l y  lake  sunbaked papa t o produce  zones a l o n g  effects  i n summer.  A rising  are profound t r a n s i e n t e f f e c t s  lesser,  unless  increased.  and c r u m b l e s when  summer.  offshore currents.  and  level  i n water  i n water  lake  l o a d s , which a r e c a r r i e d  deeper, r e v e r s e ,  If  I n L a k e Waikaremoana i n t e n s e wave e r o s i o n  e x p o s e d above t h e w a t e r  heavy papa s i l t  be  algae.  following increased  Papa b e d r o c k i n t h e drawdown zone c r a c k s  level  o f the lower  i n summer c a u s e s a r e d u c t i o n  as w e l l , t h e n t h i s  deep  t h e i r veg-  macrophytes and a l s o o f a t t a c h e d  level  level  little  With a f a l l i n g  lake lake  o f smooth c o n c r e t e and suspended papa  e x t r e m e drawdown r e a c h e s down t o t h e f i n e r  silt  sediments  -  of the  l o w e r drawdown zone.  responsible lake  level  f o r the and  cause there  are,  sufficient  are  temperature,  associated with  vegetation  A rising  lake  and  level  flowering.  summers d u r i n g  associated with  and  a rising  the  study  only  period, species  comm.) and  i t s g r o w t h and  Grimas 1 9 6 1 ) , b u t severe  survive.  the  prevent  out  emergent  the  of  lake  the  weaken any  i n New  spread.is  entirely  competicanadensis. (Fish,  vegetative.  zone n o t  T h i s commonly  drawdown zone  sur-  three  Zealand  upper l i t t o r a l  only  eliminates  (.Quennerstedt 1958, freezing i s  Scandinavia,  of n a t i v e a q u a t i c macrophytes tolerance  lake,  19 7 5 ) .  have o v e r E l o d e a  than i n n o r t h e r n  Their higher  seasonal  i f i t is  a t L a k e Waikaremoana, where t h e  or prolonged  species  may  also to.freezing.  a q u a t i c macrophytes from the  sp.)  of  lake  through f l o o d i n g of  i n two  and  reduce  a rising  level,  summer may  female p l a n t s of Elodea  d e s s i c a t i o n , but  hardy  lake  (Mitchell  in late  W i n t e r drawdown e x p o s e s t h e  less  circulation  be-  suspended  primarily related to  soil  partly  between  a l g a l blooms, which  This occurred  advantage t h a t these  There are  to  f a c t o r s , s u c h as  of a q u a t i c macrophytes from p e n e t r a t i n g  f a c e and  only  i n L a k e Waikaremoana,  f l o o d s and  Floods  be  correlation  t o p r o d u c e a damming-up e f f e c t  terrestrial  species  negative  other  A l g a l blooms, a l t h o u g h  a l s o be  pers.  significant  during  changes i n l i g h t ,  tive  S h o r e e r o s i o n may  of course,  water transparency.  may  -  water transparency  sediment i n p u t s  level.  79  Ce.g.  some  Myriophyllum  to d e s s i c a t i o n and/or  '  - 80 -  f r e e z i n g gives  these n a t i v e  species  some c o m p e t i t i v e advantage  over the adventive Elodea canadensis i n the drawdown zone. High winter lake l e v e l s p r o v i d e a measure o f p r o t e c t i o n to the weedbeds o f the shallower l i t t o r a l wave a c t i o n o f w i n t e r storms. protection  from the d i s r u p t i v e  The seasonal t i m i n g  i s a l t e r e d by h y d r o e l e c t r i c  of t h i s  development.  The major c y c l e The major c y c l e i n lake l e v e l f l u c t u a t i o n s , w i t h i t s p e r i o d i c i t y i n the order o f 2 - 5 years duce a s h i f t i n g l i t t o r a l trend  zone.  (Figure  3), w i l l  pro-  When t h i s i s showing an upward  i n the order o f 1 - 2 metres depth/year te.g. recent  post-hydroelectric  development p e r i o d  - 1970 - 1971 - F i g u r e  5) there w i l l tend t o be an upward displacement o f the lower boundary o f a q u a t i c lower drawdown zone.  macrophytes and a r e c o l o n i z a t i o n o f the P e r i o d s o f extreme drawdown (e.g. w i n t e r s  of 1969 and 1973, F i g u r e  4) w i l l f u n c t i o n as a " r e s e t " by  e l i m i n a t i n g macrophytes i n the lower drawdown zone, and i f the  lake l e v e l remains lower than u s u a l during  allowing  summer, by  some e x t e n s i o n o f macrophytes i n t o deeper water.  complex o f f a c t o r s r e l a t e d t o lake l e v e l f l u c t u a t i o n s  A  will  a f f e c t the composition o f the macrophyte beds i n the drawdown zone - e.g. e f f e c t s on s u b s t r a t e , species  resistance  o f macrophyte  to exposure, d e s s i c a t i o n and f r e e z i n g , wave a c t i o n ,  and t h e i r a b i l i t y and r a t e o f r e c o l o n i z a t i o n . The major c y c l e combined w i t h the a l t e r e d seasonal per^,  - 81 -  i o d i c i t y has  s i g n i f i c a n t impacts on the t r o u t spawning areas  i n the g a u n t l e t s .  During a low  phase of the major c y c l e  t e n s i v e areas of s u i t a b l e g r a v e l s become a v a i l a b l e to spawning t r o u t . age  length  From records  the  of the  and weight of rainbow t r o u t caught by anglers  Lake Waikaremoana data) there  d a t i n g back to 1931  (New  of the rainbow t r o u t , which seem to be c o r r e l a t e d w i t h major c y c l e of lake l e v e l f l u c t u a t i o n s .  in  have i n c r e a s e d  numbers the  I t appears t h a t  p e r i o d of a " c y c l e " i n p o p u l a t i o n  rainbow t r o u t may  aver-  Zealand W i l d l i f e S e r v i c e - unpublished  i s evidence of f l u c t u a t i o n s i n p o p u l a t i o n  amplitude and  ex-  the  numbers of  f o l l o w i n g h y d r o e l e c t r i c dev-  elopment.  The  r a t e of r i s e and The  fall  i n lake  a b i l i t y of aquatic  lake l e v e l and  level  invertebrates  to f o l l o w changes i n  avoid the danger of s t r a n d i n g  species. (Moon 1935,  Hynes 1961)  - and  varies with  the  probably v a r i e s a l s o w i t h  the time of year and water temperature. In Lake Waikaremoana e f f e c t s of lake l e v e l f l u c t u a t i o n s on the h a b i t a t and macrophytes, and  attached  than the dangers of The  food of l i t t o r a l  invertebrates  (substrate,  algae) are probably more important  stranding.  maximum r a t e of drawdown i n Lake Waikaremoana  (^6  cms/day) i s w e l l w i t h i n  the l i m i t s of the r a t e of drawdown  (15 cms/day), which was  set to p r o v i d e some p r o t e c t i o n  littoral  fauna of L l y n Tegid  f o r the  - a h y d r o e l e c t r i c lake i n North  -  Wales  (Hunt and  Jones  82  -  19 7 2 ) .  LITTORAL INVERTEBRATE FAUNA The  mean number o f a n i m a l s p e r s q u a r e m e t r e  b e l o w t h e drawdown l i m i t  i n L a k e Waikaremoana  i d u a l s p e r square metre) i s comparable animals  i n the upper  Swedish,  2 metres  Lake A n k a r v a t t n e t  m e t r e ) - see F i g u r e 27. (and to  October mm  inclusive)  mesh  (Grimas  indiv-  to the d e n s i t y  of  of the unregulated, n o r t h e r n  samples  w i t h an Ekman d r e d g e 1961).  The  per  square  i n Lake A n k a r v a t t n e t  Lake B l a s j o n ) were t a k e n d u r i n g summer and  a 0.6 in  (c± 9000  ( d 10,000 i n d i v i d u a l s  The  immediately  0.8  mm  and  autumn sieved  through  mesh, w h i c h was  L a k e Waikaremoana, w o u l d n o t have r e t a i n e d many o f  smaller  individuals  counted  (June  i n t h e A n k a r v a t t n e t and  used  the  Blasjon  samples. Water t r a n s p a r e n c y i n t h e S w e d i s h readings The  metres)  was  similar  (.< 4 months) i n t h e S w e d i s h  approximately 3 metres,  thermocline for  - 13.5  may  of thermal  (JFigure 2 7 ) .  The  and  depth the  account  littoral  depth of thermal  of the l i t t o r a l  a g i v e n a m p l i t u d e o f drawdown.  t h i s may  i n the deeper  t h e r e f o r e have a s i g n i f i c a n t  quantitative vulnerability  stratifi-  w h e r e a s i n L a k e Waikaremoana  the g r e a t e r d e n s i t y o f animals  fication  disc  lakes occurred at a  l a y a t o r b e l o w 15 m e t r e s ,  Lake Waikaremoana  (Secchi  t o L a k e Waikaremoana.  t h e r m o c l i n e , d u r i n g the s h o r t p e r i o d  cation of  9.5  lakes  influence  of  stration  the  invertebrates  to  L A K E fl N KftR VATTN E T  LAKE  BLBSTON  LAKE  Wfl I K f l R E M O f l N R  0 SOOO i i i • -i i NUMBER OF ANIMALS pvt. SQCflRe M E T R E  FIGURE 27. The d e p t h d i s t r i b u t i o n o f the bottom fauna i n Lake B l a s j o n and A n k a r v a t t n e t ( a f t e r Grimas 1961) and i n Lake Waikaremoana.  -  Quantitative  84 -  losses  Grimas a t t r i b u t e s t h e " i n v e r t e d of  animals"  to  t h e e f f e c t s o f w i n t e r drawdown.  Blasjon  i n t h e drawdown zone o f L a k e B l a s j o n  and A n k a r v a t t n e t p r o f i l e s  distribution losses  bathymetric d i s t r i b u t i o n  By s u p e r i m p o s i n g t h e of the q u a n t i t a t i v e  o f t h e b o t t o m f a u n a , he e s t i m a t e d  due t o h y d r o e l e c t r i c  a b o u t 70% i n t h e drawdown  (.Figure 27)  utilization  depth  the q u a n t i t a t i v e  o f Lake B l a s j o n a t  zone, and 2 5% b e l o w t h e drawdown  limit. Grimas a t t r i b u t e s t h e s e destruction  o f food  losses  and h a b i t a t  i n t h e drawdown  ( p a r t i c u l a r l y the e l i m i n a t i o n  o f m a c r o p h y t e s ) , more t h a n t o d i r e c t m o r t a l i t y vertebrates attributes  due t o s t r a n d i n g . the losses  as  is  deep a s t h e u p p e r p r o f u n d a l  destruction  of habitat  o f the l i t t o r a l  Blasjon.  Filter  feeders  Waikaremoana l i t t o r a l  are not numerically  fauna.  zone, w h i c h sphaeriids. of draw-  sediments  siltation  zone may be more i n t e n s e  limit  inorganic  amplitude o f winter  u n l i k e l y t o be a s e x t r e m e , b u t i n o r g a n i c i n t h e drawdown  to  i n the shallow l i t t o r a l  cooling  winter  b e l o w t h e drawdown  t o f i l t e r - f e e d e r s such as  down was n o t as e x t e n s i v e ,  erosion  extreme  i n t h e drawdown  L a k e Waikaremoana due t o t h e s m a l l e r  is  during  zone) and a l s o  o r i g i n a t i n g from e r o s i o n  especially detrimental The  he  t o an a l t e r e d t e m p e r a t u r e r e g i m e i n t h e  (an e f f e c t w h i c h e x t e n d s w e l l  siltation  of l i t t o r a l i n -  Below t h e drawdown l i m i t  s e d i m e n t s r e s u l t i n g from a b n o r m a l c o o l i n g drawdown  zone t o  from  than i n Lake  prominent i n the  -  S e a s o n a l changes i n depth  85  distribution  S e a s o n a l changes i n the i n v e r t e b r a t e s are differential seasonal  migrations  r e t a i n e d by During  a 0.8  mm  s p r i n g and  in  deep l i t t o r a l .  The  tillyardi  and  reproductive  probably The  r a t e s t o an the  winter  the not  late  instar  during  lake  the  (e.g.  live  size  and  rising  cause a bloom of a t t a c h e d  deep summer g e n e r a t i o n  i n numbers o f  respond with  i n food  supply  o f a downward increased  gastrothis.  increased  and  rising  be  samples i n l a t e  Potamopyrgus  l a r g e l y due  summer  so a p p a r e n t i n G y r a u l u s  c o u l d be  explained  larvae during winter f o l l o w i n g s p r i n g and  zone i n  migration.  numbers o f  zone may  algae  Paroxye-  associated with  zone may  increase  of  d e c r e a s e i n numbers i n t h e m i x e d  the  to  penetration  level),  by  an  upward  during  (March/April),  sp. upper  littoral  upward m i g r a t i o n  i n preparation early  t o an  phototaxis  i n c r e a s e d numbers o f O d o n a t a i n t h e  during winter  zones,  f o r some t a x a  They showed a s t r o n g p o s i t i v e  s o r t i n g of  The  r a t e s between  summer i n c r e a s e  antipodarum i n the mixed  w h i c h was  a falling  zone a r e p r o b a b l y  summer i s s u g g e s t i v e  migration.  factors;  reproductive  i n the N i t e l l a  temperature, but  During  to a combination of  summer i n c r e a s i n g l i g h t  the  Nitella  gastropods  littoral  mesh.  e n h a n c e d by  temperatures,  pods i n t h e  the  between z o n e s , and  water  thira  due  of  o l i g o c h a e t e s ) , growth to a s u f f i c i e n t  (which w o u l d be  the  depth d i s t r i b u t i o n  t o be  m o r t a l i t y and  c h i r o n o m i d s and be  likely  -  summer.  of  f o r emergence Macan  (.1977)  - 86 -  describes  an  increase  o f Odonata l a r v a e The  in their  dragonfly,  o b e r t o December. crawling  the  P r o c o r d u l i a g r a y i , emerges f r o m l a t e The  l a r v a e are  powerful their  zone) o c c u r s  The  swimmers and  final  can  of  their  but  anism i n t o the from the  (19 77)  zygopteran  depth of  zealandica  littoral  describes  the  widely summer.  show q u i t e a d i f f e r e n t  P.  l a r v a e ,'. deposited.  newly-hatched  i n f l u e n c e d by  territorial  d i s p e r s a l of o v i p o s i t i n g i n the  16).  some d i s p e r s a l mech-  g r a y i probably  Being  the  late  eggs a r e  such a d i s p e r s a l of  changes i n depth d i s t r i b u t i o n .  by  the  mixed  (Figure  early instar  l a r v a e , w h i c h a p p e a r e d t o be  bivalves  of  o f o v i p o s i t i n g by  must be  The  the  (.in t h e  grayi  littoral  a r e a s where t h e  n o t e d p r e v i o u s l y o f a d u l t male P.  The  instar  During winter  zealandica  f o r the  of wind-induced currents.  lateral  final  rapidly traverse  pattern  there  deeper l i t t o r a l  shallow  Xanthocnemis  maximum c o n c e n t r a t i o n  r e s u l t s from the  f o r X.  substrate,  l a r v a e o f O d o n a t a a p p e a r t o be  throughout the  probably  travel  a weed-free damselfly,  l a r v a e o f X.  Oct-  s l o w - m o v i n g when  emergence m i g r a t i o n .  deeper than the  early instar  dispersed  ection  are  e m e r g i n g , s l o w e r - m o v i n g l a r v a e o f P.  The  Macan  larvae  " j e t - p r o p u l s i o n " across  maximum c o n c e n t r a t i o n  grayi,  instar  emerges a b o u t a month l a t e r ;  weedbeds on  This  late  winter  year.  u p p e r drawdown zone.  zealandica,  earlier  second  water during  t h r o u g h d e n s e weed b e d s , a l t h o u g h t h e y c a n  much f a s t e r by s u c h as  i n numbers i n s h a l l o w  littoral pattern  the  dir-  behaviour ensures  some  areas. of  filter-feeders  seasonal they  might  -  be  expected  strate  i n summer d u r i n g  p e r i o d o f t h e weedbeds, b u t greater  and  the  Paroxyethira  pattern of  during winter  larvae of  the  hendersoni,  cycle  t h e weed beds  account  Pycnocentrodes  for their  similar  (e.g. T r i p l e c t i d e s  a s i n g l e year sp.  and  to complete  Nymphula n i t e n s )  i n summer, and  before  the  next generation  of  their  show  a t e m p o r a r y d e c l i n e i n numbers f o l l o w i n g emergence o f adults  may  Similar ecological  Trichopterans, may  sub-  distribution.  Those i n s e c t s , which take life  weed-free  the maximal v e g e t a t i o n a l  p r o t e c t i o n from p r e d a t i o n .  requirements of sp.  -  to f l o u r i s h b e t t e r i n a r e l a t i v e l y  - particularly  provide  87  the  larvae  appear. Following in the in  summer and  h y d r o e l e c t r i c development the reduced water transparency  primary production the  deeper l i t t o r a l ,  treme, a d i e - o f f duce an icant  of the  unseasonally  increase  Nitella may  of both attached  zone  i n the  and  i f the  p o s i t i n g by  rising  w h i c h had  level  reduce  macrophytes  level  chain.  Species  shallow  so i n t o an  level  i s ex-  The  .  pro-  signiflower  winter  1976,  event.  i n summer may  aquatic vegetation. do  lake  d e v e l o p e d by  z e a l a n d i c a , w h i c h may  w a t e r may  and  l a r v a e o f Chironominae i n the  i n t e r f e r e with  adult insects, particularly  as X a n t h o c n e m i s  probably  algae  e a r l y d e t r i t u s food  have been r e l a t e d t o s u c h an lake  will  lake  d e e p e r weed b e d s i n summer w i l l  ( F i g u r e 18),  A rising  rising  be  those  species,  d e p e n d e n t on  which d e p o s i t  their  unfavourable  ovisuch emergent  eggs i n t o  habitat.  Adult  -  88 -  f e m a l e s o f P r o c o r d u l i a g r a y i a r e a t t r a c t e d by t h e d a r k o f u n d e r l y i n g weed b e d s d u r i n g deeper water  o v i p o s i t i n g a t the surface of  (Armstrong 1958); t h e l a k e  period  (December t o M a r c h i n c l u s i v e ) may  bution  of their  During  the f i n a l  the  (late October  shallower  zone t o c r a w l in  instar  t h e drawdown  zone.  On b r i g h t  t o December i n c l u s i v e ) t h e y  o u t onto the lake  shore.  the distance  they  A rising  leave  drawdown  lake  have t o t r a v e l availability  level across  to the  T r e e stumps s p a n n i n g t h e drawdown zone p r o v i d e  escape routes An  of final  are extremely vulnerable t o  t h i s weed f r e e zone, i n c r e a s i n g t h e i r  able  this  the d i s t r i -  weed b e d s and t r a v e r s e t h e w e e d - f r e e  summer i n c r e a s e s  trout.  during  affect  emergence m i g r a t i o n  by l a r g e t r o u t c r u i s i n g  sunny d a y s  level  eggs i n t h e l i t t o r a l .  l a r v a e o f P r o c o r d u l i a g r a y i they predation  green  from  valu-  predation.  upward m i g r a t i o n  o f g a s t r o p o d s and t h e l a t e  instar  l a r v a e o f P r o c o r d u l i a g r a y i and X a n t h o c n e m i s  zealandica  winter  would n o r m a l l y  a rising  lake  level.  lowing  h y d r o e l e c t r i c development the f a l l i n g  lake  level i n  winter, with  poses a g r e a t e r  a falling  lake  t o be p a r t i c u l a r l y  Qualitative  shallow  threat of stranding,  level  i n summer.  vulnerable  i n this  than would  P. g r a y i w o u l d respect  Fol-  occur  appear  (Figure 16).  losses  Maximum s p e c i e s the  coincide with  during  diversity  water with  i n the l i t t o r a l  i t s greater variation  zone o c c u r s i n  i n s u b s t r a t e and  - 89 -  macrophyte s p e c i e s . most v u l n e r a b l e (Aass 1958).. uniformity  I t i s the shallow water fauna, which i s  to d e s t r u c t i o n by h y d r o e l e c t r i c drawdown  F l u c t u a t i n g lake l e v e l s tend to produce more  of s u b s t r a t e  i n the drawdown zone, as w e l l as  e l i m i n a t i o n of some or a l l s p e c i e s of a q u a t i c thus reducing  the likelihood  of any  high s p e c i e s d i v e r s i t y i n t h i s  the  macrophytes,  s h o r t term recovery  of a  zone.  Grimas demonstrated the e f f e c t s of h y d r o e l e c t r i c development of Lake B l a s j o n on the s p e c i e s d i v e r s i t y of the fauna by comparison w i t h Lake A n k a r v a t t n e t . s p e c i e s of chironomids i n the l i t t o r a l t n e t and  He d e s c r i b e s  i n t e r m i t t e n t p a t t e r n of emergence of the  s p e c i e s of chironomids i n Lake B l a s j o n .  The  56  a  fewer  T h i s reduces t h e i r  a v a i l a b i l i t y to t r o u t as a p r e d i c t a b l e and of food  records  zone of Lake Ankarvat-  only.27 species, i n Lake B l a s j o n .  peaked and  He  littoral  utilizable  source  ( N i l s s o n 1961). s p e c i e s d i v e r s i t y i n Lake Waikaremoana may  reduced by h y d r o e l e c t r i c development - perhaps not the amplitude of lake l e v e l f l u c t u a t i o n s , as by  have been so much by  some of  the  consequences of the a l t e r e d seasonal p e r i o d i c i t y . New  Zealand l a k e s , w i t h a low  can i l l a f f o r d to l o s e even one  s p e c i e s d i v e r s i t y anyway,  or two  species.  TROUT Species The  composition percent  composition of rainbow t r o u t and  brown t r o u t  -  caught i n the  g i l l n e t s may  in  Trapping of  the  lake.  Waiotukapuna stream system) d u r i n g species and  the  G i b b s 1973)  the  of  the  spawning runs of  the  winters of  the  r a t i o of  trout  1971,  1972  f r o m 62 18%  to  & 1973 7 6%  brown t r o u t  brown t r o u t  spawning runs c o n s i s t  4 between t h e for.  But  species,  i n s p i t e of  only  i n the  this,  t h a n brown t r o u t .  gillnets  foraging  increase  i s probably of  i n the  D u r i n g the  littoral  to  fish,  differs can  figures  be  would  capture  in  suggest trout.  through the  encountering a  importance zone o f  interactions  the  night,  net.  beat along  lake.  Both i n t r a rainbow t r o u t  i n the. s h a l l o w w a t e r o f  drawdown zone. 50  -  100  o v e r mature r a i n -  in interspecific inter-  i n brown and  daytime i n s p r i n g  dominate the  regular  t h a n brown t r o u t  t h e i r chances of  c l e a r l y observed  trout  lake  t h a n brown  s i z e dominance o f m a t u r e brown t r o u t  inter-specific be  netting  segregation  trout  actions  a  of mature  Daytime o b s e r v a t i o n s  v e l o c i t i e s i n rainbow t r o u t  t h e y r e m a i n more a c t i v e  The bow  i n the  the  the  Spatial  the  (Ewing  this discrepancy  r a i n b o w t r o u t were more v u l n e r a b l e  t h i s may  the  revealed  suggest that  If  in  major spawning streams i n  immature t o m a t u r e f i s h  accounted  higher  composition  (1976).  a f a c t o r of  partly  the  -  t r u l y represent  - compared w i t h  However, as  by  not  composition varying  programme  and  (one  90  and  early  the  ,  can  drawdown  zone.  summer l a r g e  brown  Individual  metres of  and  fish  shoreline  and  cruise  a  particu-  -  larly  during  -  September and O c t o b e r a g g r e s s i v e e n c o u n t e r s  tween brown t r o u t  c a n be o b s e r v e d , and  between brown t r o u t into  91  and  t h e drawdown zone  the o c c a s i o n a l from the deeper  h a s t e n s p o s t spawning The caught al  significant  dispersal  around  difference  i s probably related  actions,  and  to daytime  results the  be a f f e c t e d by  no  significant  size-related  difference  deep l i t t o r a l zone Later  19°C,  fish.  move t o c o o l e r emerge f r o m  At night  trout  inter-  territorial  A t n i g h t t i m e , as d a r k , and  the  t r o u t move o n t o they are and  unlikely  t h e y showed i n the  zone.  temperatures  rise  tend to leave the g e n t l y  t r o u t move i n d u r i n g  to t o l e r a t e  shore.  intraspecific  i n t h e drawdown  freq-  undoubtedly  i n s i z e between t h o s e c a u g h t  brown t r o u t  rainbow  appear  down zone  and  (a more  i n t h e deep l i t t o r -  interactions,  i n summer, i f s u r f a c e  s h o r e s and  15  and  o f t h e n e t t i n g programme, t h e r a i n b o w  to  trout  This  from the shore a f t e r  s h a l l o w s o f t h e drawdown z o n e .  imately  straying  trout  observations of  b e h a v i o u r and dominance o f t h e l a r g e r fly-fishing  rainbow  i n s i z e between brown  supports the d i r e c t  e v i d e n c e d by  encounters  the lake  i n t h e n e t s i n t h e drawdown zone  zone  interspecific  littoral  u e n t o c c u r r e n c e on t h e s t e e p e r s h o r e s ) .  be-  t h e day  higher temperatures.  to  sloping  time. The  approx-  Rainbow  brown  trout  s t r e a m mouths o r s t e e p e r s h o r e s , where t h e y  the depths  and  cruise  a s h o r t e r b e a t i n t h e draw-  before descending to the depths again - to reappear  to 2 0 minutes  later.  -  A paradoxical  the  -  s i t u a t i o n has  e r e d b a y s where brown t r o u t cruise  92  been o b s e r v e d  have b e e n s e e n t o  oxygen s u p e r s a t u r a t i o n  ance o f  brown t r o u t ,  waters of leave  sheltered  cribed  at  regation the  (where t h e  At  night)  - and  yet  i n the  calm  brown t r o u t  may  oxygen  has  r e s u l t s of  the  been  dawn,  significant spatial  rainbow t r o u t  i n the  and seg-  littoral  d i r e c t observation during  the  zone  daytime  show a v e r y c l e a r  picture  early  drawdown zone and  the  rainbow t r o u t  deeper  des-  netting  and  summer;  the over  littoral.  between l a r g e  brown t r o u t  and  small  juvenile  drawdown zone have b e e n o b s e r v e d , w h i c h gave  impression of  p r e d a t i o n by  trout  toler-  i n the  spring  the  Interactions  lets.  the  brown t r o u t  show any  daytime a n g l i n g  i n the  weedbeds o f  This  temperature  f i s h were c a u g h t a t d u s k , and  d i d not  r e s u l t s of  brown t r o u t  strong  Elodea,  Photosyn-  f o r deeper water i f the  s p a t i a l segregation during  trout  22°C.  developed  nighttime  because the  between brown and  lake  the  the  r a i s e the  these l a r g e r  some l e n g t h ,  t h r o u g h the  of  bays.  behaviour of  programme  and  constantly  fall.  The  of  may  h i g h as  i f i t becomes w e l l  t h e s e warmer s h a l l o w s  levels  shelt-  l o w e r drawdown zone j u s t above d e n s e b e d s o f  when w a t e r t e m p e r a t u r e s have been as thetic  i n some  large  predatory  trout  on  i s p e r h a p s more l i k e l y  intent,  small  juvenile  to occur  T i l s e y d e s c r i b e s p r e d a t i o n by juveniles  but  no  evidence  t r o u t was  i n the  i n L a k e Eucumbene, A u s t r a l i a  of  obtained.  s t r e a m mouth  brown t r o u t  on  (.Tilsey  a  gaunt-  rainbow 1970)  .  -  93  -  E f f e c t s of h y d r o e l e c t r i c development on a v a i l a b l e space The  lowering o f the  lake l e v e l i n 1946  the area of shallow l i t t o r a l , and i c i t y of lake  g r e a t l y reduced  the a l t e r e d seasonal  l e v e l f l u c t u a t i o n s has  period-  a profound e f f e c t on  a v a i l a b i l i t y of the reduced area of weed-free shallows. l e n g t h of s h o r e l i n e was For  the  a l s o reduced  10%  l a r g e r brown t r o u t l e n g t h  a more r e l e v a n t  s p a t i a l consideration,  the weed-free shallow l i t t o r a l has a v a i l a b i l i t y of food  of s h o r e l i n e  i s probably  although the width of  an important e f f e c t on  ( p a r t i c u l a r l y emerging d r a g o n f l y  during  spawning streams.  elopment may timing  For  t h e i r f i r s t few months i n the  a v a i l a b l e space may  o f the  the  small  larvae).  juvenile  trout,  dev-  s e l e c t i v e p r e s s u r e s f o r seasonal  immigration of j u v e n i l e t r o u t to the  and  food resources were probably not  The  increase  of the  are  hydroelectric  Even before h y d r o e l e c t r i c development the  to 6.7:1  the  l a k e , changes i n t h i s  be more important, and  have a l t e r e d the  The  l o s s - Table I I I ) .  During the p e r i o d of extreme drawdown the mature t r o u t mostly i n the  the  i n r a t i o of l i m n e t i c  lake.  limnetic  f u l l y u t i l i z e d by  : l i t t o r a l areas from  space trout. 5.8:1  w i l l have accentuated the r e l a t i v e u n d e r u t i l i z a t i o n limnetic  area.  E p i l i m n i a l temperatures i n the from year to year w i t h i n the c r i t i c a l  lake during  summer vary  approximately 2°C. above or below  tempeature f o r brown t r o u t  (ci 1 9 ° C ) .  The  of the thermocline i s such, t h a t a c o l d water refuge may  depth lie  -  some d i s t a n c e f r o m to year  but  Climatic  h a s a more i m p o r t a n t  d e v e l o p m e n t on t h e t h e r m a l  a s l i g h t warming e f f e c t  leaks on  the shore.  undoubtedly  electric  94 -  variation effect  from  than  year  hydro-  conditions i n the lake,  due t o s e a l i n g  of the shallower  i n t h e dam and summer s t o r a g e may have a c r i t i c a l  effect  t h e brown t r o u t d u r i n g some y e a r s .  Food  & condition  factor  Competition  f o r f o o d between t h e s m a l l j u v e n i l e  t r o u t appears eniles  t o be u n i m p o r t a n t ;  not only are the small juv-  t a k i n g smaller food items, but i t i s mostly  origin,  and t h e i r  falling  t h e drawdown zone s u g g e s t s  condition that  onshore  factor while  this  abundant o r e l s e n o t c o n s i s t e n t l y "limnetic  and l a r g e  of limnetic  living in  supply food i s e i t h e r not  available.  Availability of  f o o d " i n t h e drawdown zone p r o b a b l y d e p e n d s upon  w i n d a t n i g h t , when l a r v a l  t o t h e s u r f a c e and l i a b l e currents.  There  fish  to l a t e r a l  o r Daphnia a r e c l o s e  displacement  i s p r o b a b l y an e r r a t i c  by s u r f a c e  replenishment  of this  s o u r c e o f f o o d t o t h e drawdown zone, and a c o n s i d e r a b l e v a r i a tion  between e x p o s e d and s h e l t e r e d ,  sloping,  littoral  After space  and  areas.  the j u v e n i l e  of the l i m n e t i c  continuous rapid  and s t e e p and g e n t l y  t r o u t have moved o u t i n t o  zone w i t h  i t s a b u n d a n t and more o r l e s s  supply of food the r i s e growth r a t e  reflects  t h e ample  i n their  condition  factor  the ease w i t h which they can  -  fill the  t h e i r stomachs, but rainbow t r o u t  factor  s t a r t s to  clines. ship  the  fish  and  reach a s i z e of fall,  s i z e to  the  larger  l i m i t e d area of  stresses  recovery of  thereafter at  s p a c e and w i t h the  Effects  of  It  littoral  factor  littoral  area of level  of  to  brown  the  food  items.  when t h e  peak, and  be  trout  are  confounded  w i t h m a t u r i t y , ..the the  s l o w and  littoral  d e v e l o p m e n t on to quantify  ripening  incomplete  rainbow t r o u t  zone, and  zone, and Littoral  biomass of  during early  invertebrates  food  the  is  limited  interactions  the  resources  l o s s of  r e s u l t i n g from the the  to  the  insect  in  impacts of  and  the  trout  However, t h e  not  been  during  available  importance  i n f,ood cha,ins t h r o u g h b u l l y and has  lake  pupae i s a t i t s  summer, when t h e y become most  more s i g n i f i c a n t , and  the  make t h e i r most  d i e t of  larvae  production  reduction  continuing  invertebrates  d u r i n g t h e i r , emergence p e r i o d s . littoral  larger  trout.  important d i r e c t c o n t r i b u t i o n spring,  crit-  zone f o r l a r g e r  t h e i r g r e a t e r d e p e n d e n c e on  invertebrates  fluctuations.  becomes  towards  spawning i n the  the  relation-  more  spawning, but  difficult  littoral  to  de-  turn  i n the  after  when  condition  about t h i s s t a g e the  compelled  are  and  t h e i r growth r a t e  trout  hydroelectric  w o u l d be  their  (.LindstrSm 1955)  food resources of larger  cms.  small,  food s i z e  condition  p r o b a b l y p a r t l y due  may  38  c h a n g e s i n body f o r m a s s o c i a t e d  gonads and  of  and  the  Changes i n c o n d i t i o n by  -  these food items are  I t i s probable that  of  ical,  95  studied.  of smelt  - 96 -  The limnetic year  i n t r o d u c t i o n of smelt food  than  resource,  either  larval  has n o t o n l y p r o v i d e d  a v a i l a b l e f o r a longer p e r i o d of the bullies  or Daphnia, but i t a l s o c y c l e s  more o f t h e " s u r p l u s " l i m n e t i c p r o d u c t i o n areas  a valuable  into  the  t h r o u g h t h e o n s h o r e movement o f p o s t - l a r v a l  littoral smelt.  Smelt  form a g r e a t e r p r o p o r t i o n o f the d i e t  o f brown t r o u t t h a n  bow  t h e r e f o r e have b e n e f i t e d  t r o u t , and t h e i r  i n t r o d u c t i o n may  rain-  t h e brown t r o u t more. The g a t h e r i n g is  capacity of a lake  a f f e c t e d by t h e s t e e p n e s s  lowering  of the lake  ity  of t e r r e s t r i a l  o f i t s shores  l e v e l with  topography o f the l o s t  for terrestrial  littoral  food  items  (JSIorlin 1964) .  may  have r e d u c e d  the  The  lost  have  littoral  o f f r o g h a b i t a t , and f r o g s a r e  ing  t o t h e l a r g e r brown t r o u t .  on t h e s p a w n i n g o f b u l l i e s  lake  Jolly  levels  and t h e e f f e c t s o f  on t h e s p a w n i n g o f s m e l t  (.1967) d e s c r i b e s a c o n t i n u o u s  f r o m November t o l a t e A p r i l  limnetic  zone i n t h e l a t e  summer s t o r a g e  may  and f r o m m i d - S e p t In Lake  of l a r v a l  summer/early w i n t e r  lowed a p e r i o d o f h i g h l a k e l e v e l s , be d e t r i m e n t a l  fluctuat-  were n o t s t u d i e d .  i n L a k e Taupo,  a p p a r e n t gap i n t h e r e c r u i t m e n t  lake  spawning p e r i o d f o r smelt  ember t o t h e end o f J u n e i n L a k e R o t o r u a . the  pro-  important  The e f f e c t s o f m o r p h o m e t r i c c h a n g e s and f l u c t u a t i n g levels  and  availabil-  i n s e c t s t o t h e t r o u t , and t h i s w o u l d  areas  The  h y d r o e l e c t r i c development  a g r e a t e r i m p a c t on t h e r a i n b o w t r o u t . vides extensive  insects  suggesting  fish  Waikaremoana to the  o f 19 76/77 that  fol-  excessive  t o spawning o f smelt  and  -  perhaps a l s o b u l l i e s . b u l l i e s was research  97  Studies  s u g g e s t e d as  -  of  the  ecology  of  t h e most u s e f u l a r e a  smelt  for  and  continuing  a t L a k e Waikaremoana.  SUMMARY  1.  The  : m o r p h o m e t r i c c h a n g e s were v i r t u a l l y  those u s u a l l y o c c u r r i n g with l a k e , because the than being of  raised.  littoral  2.  lake  l e v e l was  periodicity  levels  than t h e i r  been r e v e r s e d  years  has  been s u p e r i m p o s e d on  T h e r e was  no  4. be  lowered  a  now  unnatural  amplitude.  due  The  rather loss  more t o  seasonal  "major c y c l e " s p a n n i n g the  annual  now  occurs  the  o l d , now  due  period-  several  but to  a recurring,  summer  storage  grass-covered,  s t r e a m - m o u t h d e l t a s , and  their  periodicity.  i n i t i a l damming-up e f f e c t ,  topography of  t e r r a c e s and  lake  and  damming-up e f f e c t  o f water, the cut  initially  a  a disproportionately great  are  has  transient  of  area.  icity  3.  reverse  h y d r o l e c t r i c development of  T h e r e was  F l u c t u a t i n g lake  altered  the  wave-  the major c y c l e  of  level fluctuations. Quantitative  assumed due  toral.  Further  sult  lake  of  l o s s e s i n the  t o the  reduction  i n the  losses i n l i t t o r a l  level  submergence o f  littoral  invertebrate total  area  production  fluctuations, particularly  t h e weed-beds and  reduced water  of the  occur due  fauna  to  as  a  can  litre-  summer  transparency.  - 98 -  5.  The  littoral  i n v e r t e b r a t e fauna i s adapted to a  lake l e v e l i n summer, and  a r i s i n g lake l e v e l i n w i n t e r .  r e d u c t i o n i n the s p e c i e s d i v e r s i t y of the l i t t o r a l which may  have occurred  falling  fauna,  f o l l o w i n g h y d r o e l e c t r i c development,  i s l i k e l y to be r e l a t e d more to the a l t e r e d p e r i o d i c i t y than the amplitude of lake l e v e l f l u c t u a t i o n s . lakes with t h e i r low even a few 6.  The  New  Zealand  species.  small j u v e n i l e t r o u t and o l d l a r g e t r o u t are most of the  de-  littoral  Because of t h e i r requirements, the c a r r y i n g c a p a c i t y  of the lake f o r t r o u t has been reduced out of p r o p o r t i o n the r e d u c t i o n i n the t o t a l area of the 7.  rather  s p e c i e s d i v e r s i t y can i l l a f f o r d to l o s e  pendent on the space and/or food resources zone.  Any  Rainbow t r o u t dominate n u m e r i c a l l y ,  inate i n s i z e .  to  lake. but brown t r o u t dom-  Rainbow t r o u t have probably  been more  adversely  a f f e c t e d by the changes f o l l o w i n g h y d r o e l e c t r i c development than brown t r o u t .  Brown t r o u t appear to have b e n e f i t e d more  from the i n t r o d u c t i o n of smelt. 8.  The morphometric changes i n the l a k e are now  " h i s t o r i c a l " and  l a r g e l y of  academic i n t e r e s t , but f l u c t u a t i n g lake  levels,  being a c o n t i n u i n g impact, are of more concern to Management. A more d e t a i l e d understanding of the ecology  of the  i n v e r t e b r a t e s and n a t i v e f i s h i s needed before  littoral  the s i g n i f i c a n c e  of the a l t e r e d p e r i o d i c i t y of the lake l e v e l f l u c t u a t i o n s can be f u l l y a p p r e c i a t e d .  However, i t i s probably  t h a t any measures to r e s t o r e the seasonal  safe to assume  p e r i o d i c i t y back  -  towards the n a t u r a l  99 -  s i t u a t i o n w o u l d be  MANAGEMENT  desirable.  IMPLICATIONS  A c o u n t r y w h i c h d e p e n d s l a r g e l y on h y d r o e l e c t r i c committed  t o maximum h y d r o e l e c t r i c  power i s  power g e n e r a t i o n d u r i n g  w i n t e r months.  The e c o l o g i c a l i m p a c t s o f a summer  winter  seasonal p e r i o d i c i t y i n the l e v e l s of t h e i r  drawdown  hydroelectric If  lakes  t h e r e was  power and t h e r m a l could the  an o p t i m a l b a l a n c e between  down f o r m a i n t e n a n c e  summer. o p e r a t e most e f f i c i e n t l y  t i n u o u s h i g h o u t p u t , and c o u l d  fluctuations  t o a more n a t u r a l  Alternatives  hydroelectric  lakes  lakes  power w o u l d n o t o n l y  and r i v e r  i m p a c t s on a l r e a d y reservoirs.  to  amplitude.  from development, b u t c o u l d  harmful  pro-  would a l l o w the  s e a s o n a l p e r i o d i c i t y and  to hydroelectric  reduce the c o n t i n u i n g  This  i n existing hydroelectric  r e m a i n i n g r i v e r s and l a k e s  a t con-  be u s e d t o meet a g r e a t e r  o f t h e w i n t e r power demands.  level  revert  power  t h e summer months, e s p e c i a l l y i f  T h e r m a l power s t a t i o n s  lake  hydroelectric  (.or n u c l e a r ) power, t h e h y d r o e l e c t r i c  t h e r m a l power s t a t i o n s were c l o s e d  portion  storage/  are unavoidable.  be u s e d more d u r i n g  during  the  save also  developed  - 100 -  LITERATURE  Aass,  CITED  P. 1958. The e f f e c t s o f impoundment on i n l a n d f i s h e r i e s . I n t e r n a t . Union f o r C o n s e r v a t i o n o f Nature and N a t u r a l Resources. Seventh T e c h n i c a l Meeting, Athens, Greece. 9 pp.  A n d e r s o n , G.P. 1948. Waikaremoana - The p r o b l e m t r o l P r o c e e d i n g s N.Z.I.E.  of lake  con-  A r m s t r o n g , J . S . 1958. The b r e e d i n g h a b i t s o f t h e C o r d u l i i d a e (Odonata) i n t h e Taupo d i s t r i c t o f New Z e a l a n d . Trans. Roy. S o c . N.Z. 85: 275-282. A x e l s s o n , J . 1961. Z o o p l a n k t o n a n d impoundment o f two l a k e s i n n o r t h e r n Sweden ( R a n s a r e n and K u l t s j o n ) . Rep. I n s t . Freshw. Res., D r o t t n i n g h o l m . 42: 84-168. Beckman, W.C. 1966. I n d i s c u s s i o n - The b i o l o g y o f r e s e r v o i r s i n t h e U.S.S.R. P r o c . Symp. I n s t . B i o l . 15: 154. B u r s t a l l , P . J . 1975. I n "New Z e a l a n d L a k e s " . Auckland University Press. E d i t o r s , V.H. J o l l y and J.M.A. Brown. Sport f i s h e r i e s . Ch. 22: 308 - 318. C a m p b e l l , R.N. 1957. The e f f e c t o f f l o o d i n g on t h e g r o w t h r a t e o f brown t r o u t i n L o c h Tummel. S c i . I n v e s t . F r e s h w a t . Fish. Scot. 14: 7 p p . . 1963. Some e f f e c t s o f impoundment on t h e e n v i r onment a n d g r o w t h o f brown t r o u t (Salmo t r u t t a L . l i n Loch Garry ( I n v e r n e s s - s h i r e ) . S c i . I n v e s t . Freshwat. Fish. Scot. 30: 2 7pp. C a r t e r , N.R. 1951. L a k e Waikaremoana, New Z e a l a n d . Union Geodesique e t Geophysique I n t e r n a t i o n a l e , B r u x e l l e s . E x t r a i t du Tome I I I : 385-399. E l l i o t t , J.M. 1971. Some methods f o r t h e s t a t i s t i c a l a n a l y s i s o f samples o f b e n t h i c i n v e r t e b r a t e s . F.B.A. Scientific Publ. 25. 14 8 pp. E l d e r , H.Y. 1965. 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E f f e c t s o f h y d r o e l e c t r i c development i n w e s t e r n Canada on a q u a t i c ecosystems. J., F i s h . R e s . Board Can. 31(5): 913-927. G r i m a s , U. 1961. The b o t t o m f a u n a o f n a t u r a l and impounded l a k e s i n n o r t h e r n Sweden ( A n k a r v a t t n e t and B l a s j o n ) . Rep. I n s t . Freshw. Res., D r o t t n i n g h o l m . 42: 183-237. . 1962. The e f f e c t o f i n c r e a s e d w a t e r l e v e l f l u c t u a t i o n upon t h e b o t t o m f a u n a i n Lake B l a s j o n , n o r t h e r n Sweden. Rep. I n s t . F r e s h w . R e s . , D r o t t n i n g h o l m . 44: 14-41. . 1965. E f f e c t s o f impoundment on t h e b o t t o m f a u n a of h i g h mountain l a k e s . A c t a U n i v e r s i t a t i s U p s a l i e n s i s . 51: 5-24. Hunt, P.C. a n d J.W. J o n e s . 1972. The e f f e c t o f w a t e r f l u c t u a t i o n s on a l i t t o r a l f a u n a . J. Fish. Biol. 385-394. H u t c h i n s o n , G.E. 1957. A T r e a t i s e on L i m n o l o g y , W i l e y . N.Y.: 580-582.  level 4:  V o l . I.  Hynes, H.B.N. 1961. The e f f e c t o f w a t e r l e v e l f l u c t u a t i o n s on the l i t t o r a l fauna. Verh. I n t e r n a t . V e r e i n . Limnol. 14: 652-656. I r w i n , J . 1977. L a k e Waikaremoana, B a t h y m e t r y , N.Z. O c e a n o g r . I n s t . C h a r t . L a k e S e r i e s .  1: 16,000.  J o l l y , V.H. 1967. O b s e r v a t i o n s on t h e s m e l t R e t r o p i n n a lacustris Stokell. N.Z. J o u r n . S c i . 1 0 ( 1 ) : 330-355. L i n d s t r o m , T. 1955. On t h e r e l a t i o n f i s h s i z e - f o o d s i z e . Rep. I n s t . F r e s h w . R e s . , D r o t t n i n g h o l m . 36: 133-147. . 1973. 145-153.  Life  i n a lake reservoir.  Ambio.  2(5):  - 102 -  Macan, T.T. 1977. The f a u n a i n t h e v e g e t a t i o n o f a m o o r l a n d f i s h p o n d a s r e v e a l e d b y d i f f e r e n t methods o f c o l l e c t i n g . Hydrobiol. 55 C D : 3-15. and E.B. W o r t h i n g t o n . 1951. L i f e i n L a k e s a n d Rivers. C o l l i n s Press. London, p. 102. M a r p l e s , B . J . 1962. An i n t r o d u c t i o n t o f r e s h w a t e r l i f e i n New Z e a l a n d . C h r i s t c h u r c h , Whitcombe a n d Tombs. 160pp. McMynn, R.G. a n d P.A. L a r k i n . 1953. The e f f e c t s o n f i s h e r i e s o f p r e s e n t and f u t u r e water u t i l i z a t i o n i n t h e Campbell River drainage area. B.C. Game Comm. Mgmt. P u b l . 2: 1-61. M i n s t e r , J . B . , T.H. J o r d a n , P. M o l n a r and E . H a i n e s . 1974. Numerical modelling o f instantaneous Plate Tectonics. Geophys. J.R. a s t r . S o c . 36: 541-576. M i t c h e l l , S.F. 1975. Some e f f e c t s o f a g r i c u l t u r a l d e v e l o p m e n t and f l u c t u a t i o n s i n w a t e r l e v e l on t h e p h y t o p l a n k t o n p r o d u c t i v i t y a n d z o o p l a n k t o n o f a New Z e a l a n d r e s e r v o i r . Freshwat. B i o l . 5: 547-576. Moon, H.P. 1935. F l o o d movements o f t h e l i t t o r a l Windermere. J . Anim. E c o l . 4: 216-228.  fauna o f  Mundie, J.H. 1957. The e c o l o g y o f C h i r o n o m i d a e i n s t o r a g e reservoirs. T r a n s . Roy. e n t . S o c . L o n d . 109: 149-232. N i l s s o n , N-A. 1961. The e f f e c t o f w a t e r l e v e l f l u c t u a t i o n s on t h e f e e d i n g h a b i t s o f t r o u t and c h a r i n t h e l a k e s B l a s j o n and J o r m a s j o n , N o r t h Sweden. Rep.. I n s t . F r e s h w . Res., D r o t t n i n g h o l m . 42: 238-261. . 1964. 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