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The effect of age and environmental factors on the vertical migration and distribution of Chaoborus flavicans… Teraguchi, Mitsuo 1964

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THE EFFECT OF AGE AND ENVIRONMENTAL FACTORS ON THE VERTICAL MIGRATION AND DISTRIBUTION OF CHAOBORUS FLAVICANS (MEIGEN) LARVAE by Mitsuo Teraguchi B i S c , U n i v e r s i t y of B r i t i s h Columbia, 1962  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA October, 1964  In the  r e q u i r e m e n t s f o r an  British  mission  for reference  for extensive  p u r p o s e s may  be  cation  of  written  the  study*  copying of the  for  in partial  degree at  the  Library  this thesis  Head of my  agree for  of  not  permission*.  Z n n l ngy  The U n i v e r s i t y of B r i t i s h Vancouver 8 Canada f  Date  August 28, 1964  , Columbia,  of •  per-  scholarly  Mitsuo Teraguchi  Department  that  or  c o p y i n g or  shall  of  make i t f r e e l y  Department  that  f i n a n c i a l gain  fulfilment  University  shall  I further  I t i s understood  this thesis  w i t h o u t my  that  and  g r a n t e d by  representatives.  this thesis  advanced  Columbia, I agree  available  his  presenting  be  by publi-  allowed  ABSTRACT The e f f e c t of age and some environmental  factors, especially  l i g h t , on the v e r t i c a l migration and d i s t r i b u t i o n of Chaoborus f l a v i c a n s larvae were studied both i n the f i e l d and i n the laboratory a t Corbett Lake, B r i t i s h Columbia during the summer of 1963. D i s t r i b u t i o n and migration of Chaoborus larvae were studied l a r g e l y by frequent h o r i z o n t a l Clarke-Bumpus plankton tows made at 1 metre i n t e r v a l s from the surface almost to the maximum depth of the l a k e .  Marked d i f f e r e n c e s were noted i n daytime  v e r t i c a l d i s t r i b u t i o n and d i e l migration of 5 s i z e (or age) classes of l a r v a e .  These size classes probably corresponded  approximately to l a r v a l i n s t a r s .  Class 0 and 1 larvae inhabited  the epilimnion i n the daytime throughout the summer, while c l a s s 4 larvae were l a r g e l y confined to the hypolimnion during the day. Class 2 and 3 larvae occupied the e p l - , meta-, and hypolimnion i n the daytime during June and J u l y , but were found c h i e f l y i n the hypolimnion during August and September.  Only the older  larvae ( c l a s s 2, 3 and 4) underwent marked d i e l v e r t i c a l migration which consisted of 4 phases: depth to the surface,  l ) daydepth,  2) ascent from day-  3) gradual descent from surface,  descent during dawn. The ascent occurred when subsurface  4) r a p i d light  was r a p i d l y diminishing a t dusk, while the descent took place during darkness and was most marked when l i g h t s t a r t e d to penetrate the subsurface l a y e r s during dawn. Seasonal changes i n timing of ascent and descent appeared to be c o r r e l a t e d to seasonal changes i n time of disappearance of subsurface l i g h t i n t e n s i t y  during dusk.  The rates of ascent and descent c a l c u l a t e d from  the a n a l y s i s of echo traces were 13.6 and 1.1 m/hr r e s p e c t i v e l y . Further a n a l y s i s of the echo traces revealed that the Chaoborus s c a t t e r i n g l a y e r was i n contact w i t h the lake basin during daytime and descent, but not during ascent. Results from observations of l a r v a l migration i n experimental tubes housed i n a dark room corroborated those of the f i e l d . Class 2 larvae having s i m i l a r daytime v e r t i c a l d i s t r i b u t i o n (surface and 5 m) as c l a s s 0 and 1 larvae underwent v i r t u a l l y no d i e l v e r t i c a l migration i n the tubes, while c l a s s 2 and 3 larvae taken from the deeper l a y e r s (10-14 m) of the lake d i d . The d i e l migration consisted of the same 4 phases observed i n the f i e l d , as w e l l as a "dawn r i s e " phase which was evident f o r c l a s s 3 l a r v a e .  particularly  Complete migration cycles were  induced by a r t i f i c i a l l y changing the n a t u r a l l i g h t i n t e n s i t y over an experimental tube during the period of r e l a t i v e l y l i g h t (0900-1900 hours);  constant  the larvae responded most markedly  to changes i n l i g h t i n t e n s i t y at the 0-1000 l u x range.  Experiments  i n d i c a t e d that the d i e l v e r t i c a l migration of Chaoborus larvae i s an exogenous rhythm c o n t r o l l e d by l i g h t .  ACKNOWLEDGEMENTS This study has been supported by the B r i t i s h Columbia F i s h and Game Branch and the I n s t i t u t e of F i s h e r i e s , Univers i t y of B r i t i s h Columbia.  The advice and s t i m u l a t i n g c r i t i c i s m  given by Dr. T. G. Northcote during the study and i n preparation of the manuscript have been g r e a t l y appreciated.  The invaluable  assistance of T. G. Halsey, R. D. Humphreys and E. R. Zyblut deserves s p e c i a l thanks.  The occasional assistance of P.  Gallagher, G. Hazelwood and D. L. McKay i n s o r t i n g plankton samples has been appreciated.  The use of property and accommoda-  t i o n of the l a t e Mr. Gibson Shaler and Mrs. Eve Shaler has been most h e l p f u l .  The c r i t i c a l reading of the t h e s i s by  Dr. I . E. E f f o r d , Dr. K. Graham and Dr. C. C. Lindsey i s g r a t e f u l l y acknowledged.  iii TABLE OP CONTENTS  Page  Abstract  i  Table of Contents  i i i  L i s t of Figures  v  L i s t of Tables  • . .... . • •  L i s t of Appendices  x  Acknowledgements . . . . . . . . . . Introduction . . . . .  x i i  . . . . . . . . . . . . .  1  Description of the Study Area P h y s i c a l and Chemical Features  3 . . . . . . . . . . .  B i o l o g i c a l Features . . . . . . . M a t e r i a l s and Methods  ix  3  .....  3  . .  4  Part 1. F i e l d Studies  4  Part 2. Laboratory Studies  9  Results  .......  12  Part 1. F i e l d Studies  12  L a r v a l Size (or Age) Classes  12  The V a l i d i t y of the L a r v a l Size (or Age) Classes as Instars  13  Abundance of L a r v a l Groups and t h e i r Daytime Vertical Distribution . . . . . . . . . . . . .  16  Seasonal V a r i a t i o n i n Horizontal D i s t r i b u t i o n  .  17  D i f f e r e n t i a l Migratory Behavior of the L a r v a l Classes . . . . . . . .  19  Migration Pattern of the Older Larvae  24  .....  Other Aspects of the D i e l V e r t i c a l Migration . .  29  i  v  Page Part 2. Laboratory Studies  32  D i e l V e r t i c a l M i g r a t i o n Under Experimental Conditions . . . . . . . . . . . . . . . . . .  32  Role of Light on D i e l V e r t i c a l Migration . . .  39  Discussion . . . . . . . • • • . . • • • . • • • . . . .  43  Seasonal V a r i a t i o n i n Horizontal  Distribution... . .  43  The E f f e c t of Age and Environmental Factors on Vertical Distribution . . . . . . . . . . . . . . .  44  The E f f e c t of Age and Environmental Factors on D i e l V e r t i c a l Migration  46  Theoretical I n t e r p r e t a t i o n Migration . . . . . .  52  B i o l o g i c a l Significance Migration  of the D i e l V e r t i c a l . . . . . . . . . .  of the D i e l V e r t i c a l . . . . . . . . . . . . . . .  L i t e r a t u r e Cited Appendices . . . . . . . . .  53 55  .  59  V  LIST OP FIGURES Figure 1.  Page Map of Corbett Lake showing contour l i n e s i n metres, l o c a t i o n of sampling Station 1, Cross Section A, i n l e t and o u t l e t streams  5  2* A* The darkroom used to study experimentally the d i e l v e r t i c a l migration of Chaoborus f l a v i c a n s larvae. B. Cross s e c t i o n a l view of the darkroom showing the arrangement of the p l a s t i c tubes used to hold the Chaoborus f l a v i c a n s larvae 3.  11  The length frequency d i s t r i b u t i o n of the Chaoborus f l a v i c a n s larvae c o l l e c t e d during the 1100 hour sampling periods of the 24 hour f i e l d s e r i e s of June 16-17, J u l y 20-21, August 17-18 and September 21-22, 1963. The v e r t i c a l arrows i n d i c a t e means, while the v e r t i c a l bars mark the points of overlap of the calculated t h e o r e t i c a l normal curves  4.  . . . . . . . . .  14  The daytime v e r t i c a l d i s t r i b u t i o n and r e l a t i v e abundance of the l a r v a l classes of C. f l a v i c a n s i n Corbett Lake based on samples c o l l e c t e d during the 1100 hour sampling periods of the 24 hour f i e l d series of June 16-17, J u l y 20-21, August 17-18 and September 21-22, 1963; oxygen and temperature conditions are also shown f o r each period  18  VI  Figure 5.  Page The v e r t i c a l d i s t r i b u t i o n of c l a s s 0, 1, 2, 3 and 4 larvae of C. f l a v i c a n s i n Corbett Lake during the 1100, 2100 and 0500 hour periods of the June 16-17 and J u l y 20-21 s e r i e s , 1963 . . . . . . . . . . . . . * . . • »  6.  22  The v e r t i c a l d i s t r i b u t i o n of c l a s s 0, 1, 2, 3 and 4 larvae of C. f l a v i c a n s i n Corbett Lake during the 1100, 2100 and 0500 hour periods of, the August 17-18 and September 21-22  7.  s e r i e s , 1963  ,23  The d i e l v e r t i c a l migration of c l a s s 2, 3 and 4 larvae of C. flavicans during September 1222 s e r i e s of 1963.  The broken l i n e s represent  the 14.8°, 12° and 6° C isothe rms; the s o l i d l i n e s represent the 1.0 lux isolume 8.  ......  26  The d i e l v e r t i c a l migration of the C. f l a v i c a n s larvae i n Corbett Lake during June 16-17, J u l y 20-21, August 17-18 and September 21-22 s e r i e s , 1963.  Surface temperature and 10°, 5°, 4° and  3.5° C temperature depths are shown.  The 0.1,  1, 10 and 100 lux isolumes are i n d i c a t e d with solid lines 9.  Echo sounding traces across Corbett Lake a t Cross Section A, October 1-2, 1962 (differences  28  vxx Figure  Page i n length of trace caused by v a r i a t i o n i n length of run or boat speed; background noise may be ignored). due" l a y e r .  The arrows i n d i c a t e the " r e s i -  Time expressed i n hundred hours  ( P a c i f i c Standard Time) . . 10.  31  D i e l v e r t i c a l migration of class 2 larvae ( c o l l e c t e d from the surface and 5 m depth of Corbett Lake) i n adjacent experimental tubes during August 13-14, 1963.  Light i n t e n s i t i e s  at the surface of both tubes were i d e n t i c a l , as were temperatures at the surface, 100 cm depth and bottom 11.  34  D i e l v e r t i c a l migration of class 3 larvae i n the experimental tube during J u l y 16-17, 1963 at Corbett Lake.  Surface l i g h t i n t e n s i t i e s  (measured with the submarine photometer) and temperatures s t surface, 100 cm depth and bottom of the tube are shown.  Probable surface l i g h t  i n t e n s i t i e s f o r .1900, 2000 and 2100 hours ( i f Photovolt Photometer was used) are i n d i c a t e d with s o l i d dots joined with a s o l i d l i n e . . . . 12.  35  D i e l v e r t i c a l migration of class 2 and 3 larvae i n adjacent experimental tubes during August 16-17, 1963*  L i g h t i n t e n s i t i e s at the surface of both  tubes were i d e n t i c a l , a s were temperatures at the surface, 100 cm depth and bottom  36  viii Figure 13.  Page D i e l v e r t i c a l migration of class 2 and 3 larvae i n adjacent experimental tubes during . September 13-14, 1963. L i g h t i n t e n s i t i e s at the surface of both tubes were i d e n t i c a l , a s were temperatures at the surface, 100 cm depth, and bottom  14.  37  The v e r t i c a l movements of c l a s s 3 larvae i n adjacent c o n t r o l (exposed to n a t u r a l l y changing l i g h t conditions) and non^control (exposed to a r t i f i c i a l l y changing l i g h t conditions) experimental tubes on August 9, 1963.  Identical  temperature conditions i n both tubes; i d e n t i c a l l i g h t i n t e n s i t y over both tubes at the beginning, and end of experiment. 15.  41  The v e r t i c a l movements of class 3 larvae i n adjacent control (exposed to n a t u r a l l y changing l i g h t conditions) and non-control (exposed to a r t i f i c i a l l y changing l i g h t conditions) e x p e r i mental tubes on September 28, 1963.  Identical  temperature conditions i n both tubes; i d e n t i c a l l i g h t i n t e n s i t y over both tubes at the beginning and end of experiment  42  LIST OP TABLES Table 1.  P§,ge Comparison of the monthly t o t a l v e r t i c a l hauls taken at randomly selected s t a t i o n s w i t h No. 10 Wisconsin net, at Corbett Lake i n 1963  20  X  LIST OP APPENDICES Appendix I  Page Determination of the c a l i b r a t i o n value of the Clarke-Bumpus sampler towed at several depths f o r a 61 m distance at boat speed of 2.5 knots  II  59  Volume of water passed through and the number of Chaoborus larvae caught by the ClarkeBumpus sampler (with No. 10 net attached) towed at several depths f o r a 61 m distance at a boat speed of 2.5 knots  III  60  Comparison of the volume of water i n the compartments of the subsampler using d i f f e r e n t t o t a l volumes  IV  61  Test of r e l i a b i l i t y of the subsampler, using d i f f e r e n t volume of water and d i f f e r e n t number of larvae.  V  A 0.05 s i g n i f i c a n c e l e v e l was used.  62  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during the 24 hour f i e l d s e r i e s of June 17-18, .1963. .  VI  65  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during the 24 hour f i e l d series of J u l y 20-21, 1963. . . .  67  XI  Appendix VII  Page Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during the 24 hour f i e l d s e r i e s of August 18-19, 1963 . . . .  VIII  . . .  69  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during the 24 hour f i e l d series of September 21-22, 1963  IX  71  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l counts of larvae i n samples taken during the 24 hour f i e l d . s e r i e s of June 16-17, 1963 . . . .  X  76  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l counts of larvae i n samples taken during the 24 hour f i e l d s e r i e s - o f J u l y 20-21, 1963 . . . .  XI  78  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l counts of larvae i n samples taken during the 24 hour f i e l d series of August 18-19, 1963 . . .  80  INTRODUCTION The larvae of the dipteran genus Chaoborus (or Corethra) are macroplankters f r e q u e n t l y i n h a b i t i n g ponds ( M i a l l , 1895; Krogh, 1911) and lakes (Muttkowski, 1918; Juday, 1921; Rawson, 1930; Eggleton, 1932; Berg, 1937; M i l l e r , 1941; Deonier, 1943; L i n d q u i s t and Deonier, 1943; Davis, 1955; Dendy, 1956; food, 1956; Woodmanse and Grantham, 1961).  They are e a s i l y recognized  by t h e i r transparent bodies and black paired a i r sacs. Although there are several species i n the genus, they have similar l i f e histories.  The l a r v a l stage l a s t s u s u a l l y f o r  about 6-7 weeks (sometimes as long as a y e a r ) , during which time the animals undergo 4 or p o s s i b l y 5 i n s t a r s (Muttkowski, 1918; Deonier, 1943; MacDonald, 1956).  In general the larvae  feed on organisms ranging from phytoplankton to aquatic i n s e c t s . Deonier (1943) has shown however that the food habits of Chaoborus astictopus d i f f e r w i t h i n s t a r s , the l a s t 2 - 3 s t a d i a p r e f e r r i n g cladocerans and copepods. The most s t r i k i n g aspect of the ecology of Chaoborus i s a marked d i e l v e r t i c a l migration, a c h a r a c t e r i s t i c of many planktonic organisms.  T y p i c a l l y the migration cycle involves  an ascent of daytime benthic larvae into the l i m n e t i c zone (to or near the lake surface) about sunset, and a descent which begins i n the f o l l o w i n g e a r l y morning hours and i s completed about dawn (Juday, 1921; Berg, 1937; Davis, 1955; Wood, 1956; Hamilton, 1961; Woodmanse and Grantham, 1961).  Atypically i t  c o n s i s t s of an ascent of l a r v a e , i n h a b i t i n g the deep layers of the lake (but not adjacent to the bottom) during the daytime,  to the upper s t r a t a during the n i g h t and a subsequent descent to the lower s t r a t a during the e a r l y morning hours (Dendy, 1956).  In both cases the migrating larvae must encounter  changes i n pressure, d i s s o l v e d gases ( e s p e c i a l l y oxygen), as w e l l as steep temperature gradients i n the summer i f the lake i s eutrophic. Few studies have been made on the e f f e c t s (both d i e l and seasonal) of age and environmental migration pattern of Ghaoborus l a r v a e .  f a c t o r s on the basic Several workers have  shown that younger larvae remain i n the l i m n e t i c zone, while the older larvae only temporarily i n h a b i t i t a t night (Eggleton, 1932; Berg, 1937; MacDonald, 1956; Yfood, 1956; Woodmanse and Grantham, 1961).  The age and size at which t h i s marked change  in' migratory behaviour  occurs, or the f a c t o r s responsible f o r  i t s timing, have not been determined i n any d e t a i l . The purpose of t h i s study was to examine the e f f e c t of age and several environmental  f a c t o r s on the v e r t i c a l migration  and d i s t r i b u t i o n of Chaoborus larvae.  Such a study may  contribute a d d i t i o n a l knowledge to the phenomenon of v e r t i c a l migration by planktonic organisms, a subject which has been extensively reviewed 1961; Raymont, 1963).  (Cushing, 1955; Hardy, 1956; Bainbridge,  3 DESCRIPTION OP THE STUDT AREA P h y s i c a l and Chemical Features Corbett Lake i s located on the southern i n t e r i o r piateau of B r i t i s h Columbia a t an e l e v a t i o n of 1068 m and about 15 km southeast of M e r r i t t .  The lake has a surface area bf 24.2  hectares, a mean depth of 6i8 m and a maximum depth of 19 m. I t becomes thermally s t r a t i f i e d e a r l y i n the season w i t h u s u a l l y no measurable amount of oxygen i n the hypolimnion (below 8 m ) .  The lower layers of the lake contain H^S.  Vernal and autumnal c i r c u l a t i o n do occur, but are not always complete because the lake i s protected from wind a c t i o n . The lake has a d i s s o l v e d s o l i d content of 336 parts per m i l l i o n . The o u t l e t stream a t the south-west corner of the lake and an i n l e t entering the north-east end ( F i g . l ) flow only during e a r l y s p r i n g . The bottom of the l i t t o r a l zone extends to a depth of about 4.5 m and i s covered with "marl" and dense shoals of chara.  The benthal of the l i m n e t i c region i s covered with  "marl" and s o f t black mud.  Biological  Features  The lake contains only stocked populations of rainbow t r o u t Salmo g a i r d n e r i and brook t r o u t Salvelinus f o n t i n a l i s which are o c c a s i o n a l l y subject to w i n t e r k i l l . The dominant organisms i n h a b i t i n g the l i t t o r a l zone are the amphipod H y a l l e l a azteca, chironomid larvae and gastropod  4 Gyraulus sp. (Humphreys, 1964). Numerous plankters i n h a b i t the l i m n e t i c zone.  Daphnia  pulex and Daphnia rosea are dominant cladocerans, while Diaptomus leptopus and Diaptomus nudus are the common copepods. Chaoborus f l a v i c a n s , C. americanus and C. nyblaei were present i n Corbett Lake with C. f l a v i c a n s being by f a r the most abundant (about 96$ of the i n d i v i d u a l s sampled).  MATERIALS AND METHODS Part 1. F i e l d Studies The a i r and lake temperatures were measured using a ColePalmer (Model 8425) thermistor with a r a p i d responding probe. Temperature s e r i e s were taken only at s t a t i o n 1, the deepest part of the l a k e . The surface and subsurface l i g h t i n t e n s i t i e s were measured at s t a t i o n 1 with a submarine photometer (Model 15-M-02/1-G.M. Manufacturing Co.) equipped w i t h Weston Photronic P h o t o e l e c t r i c "deck" and "sea" c e l l s .  L i g h t i n t e n s i t i e s recorded i n micro-  ampere u n i t s were converted to foot-candles using a Photovblt (Model 200) photometer c a l i b r a t e d d i r e c t l y i n foot-candles. Cloud cover c o n d i t i o n s , wind d i r e c t i o n s and wind v e l o c i t i e s were recorded a t each sampling p e r i o d . Water samples taken monthly with a Kemmerer b o t t l e before or a f t e r each 24 hour sampling.series were analyzed f o r oxygen using an unmodified Winkler Method. A Furuno (Model F-701) 200-kc/sec Sounder was used to make echo t r a c e s .  In 1962 echo traces were made at s t a t i o n 1  FIGURE 1.  Map of Corbett Lake showing contour l i n e s i n metres, l o c a t i o n of sampling S t a t i o n 1, Cross Section A, i n l and o u t l e t streams*  and Cross-section A ( F i g . l ) using a gain of about 5.75 while the boat was moving at about 1.5 knots (2.9 km/hr).  In 1963  traces were made only at s t a t i o n 1 using a gain of 6 and a boat speed of about 0.5 knots (2.8 km/hr).  Traces were taken  u s u a l l y before and a f t e r plankton sampling at s t a t i o n 1 and about every 15 minutes during dawn and dusk at.Cross Section A.  The s c a t t e r i n g layers on the traces have been shown by  Northcote (1964) to be l a r g e l y Chaoborus larvae. A Clarke-Bumpus  sampler f i t t e d w i t h a No. 10 (0.13  mm)  nylon n e t t i n g was attached to a 4 mm diameter wire towing cable.  A 13.6 kgm torpedo-shaped lead weight was t i e d to the  end of the cable. S t a t i o n 1 was the s i t e of plankton sampling i n both 1962 and 1963.  The sampler was towed at each sampling depth (surfac  and every metre almost to the bottom) f o r 0.5 or 1 minute. Appropriate corrections were made f o r wire angle. A f t e r each tow the net was washed by splashing water on i t , while the sampler bucket was cleaned by water squirted from a rubber syringe.  Samples were preserved i n 10fo formalin s o l u t i o n .  Twenty-four hour sampling s e r i e s were c a r r i e d out i n August and September, 1962 and u s u a l l y once a month during the summer (June-September) i n 1963.  S i x sampling periods  (every 4 hours) were c a r r i e d out during the 24 hour s e r i e s i n 1962, while 8 were u s u a l l y maintained during each series i n 1963.  In the l a t t e r year sampling was c a r r i e d out every 4  hours during the daytime (0800-1900 hours - P a c i f i c Standard Time) and every 2 hours at dawn and dusk periods (0400-0600  " hours and 1900-2300 hours). For both years echo t r a c e s , l i g h t , temperature and oxygen measurements were made during each sampling period. F i e l d c a l i b r a t i o n of the sampler was attempted i n 1963 i n a s i m i l a r manner t o that described by Clarke and Bumpus (1950).  The sampler was towed f o r a 61 m distance a t p r e c i s e l y  2.5 knots.  T r i p l i c a t e tows were made at each desired depth  (surface 2, 4, 6, 8, 10 and 12 m - uncorrected depths); t h i s was done with and without a No. 10 net attached to the sampler. As the c a l i b r a t i o n values f o r the sampler with and without the net were unusually high (Appendix 1), a 4.1 l i t e r s / r e v o l u t i o n value extrapolated from the study of Xentsch and Duxsbury  (1956)  was used. Although a comparable volume of water passed through the sampler (with No. 10 net attached) during t r i p l i c a t e tows, the t r i p l i c a t e samples obtained did not i n a l l cases contain comparable numbers of Chaoborus larvae (Appendix I I ) .  The r e s u l t s  suggested that the v a r i a b i l i t y was not due to inconsistency i n operation of the sampler, but rather to the larvae being clumped i n nature. Total counts were made f o r a l l samples c o l l e c t e d i n 1962 and f o r most of those obtained i n 1963.  Estimated counts  using a subsampler modified from Elgmork (1959) were made f o r 1963 samples containing 2000-4000 larvae.  The r e l i a b i l i t y of  the subsampler was examined using a chi-square t e s t f o r randomness (Lund et a l , 1958).  The subsampler gave random subsamples  (Appendices I I I and I V ) . One-sixth of a sample was u s u a l l y  8 taken f o r estimating t o t a l counts, while l / 2 , l/8 or 1/36 portions were taken f o r determining length of larvae.  Total  and estimated counts were made f o r some samples to check accuracy.of estimates. The distance ( i n mm) between the p o s t e r i o r end of the thoracic a i r bladders and the a n t e r i o r t i p of the abdominal bladders was measured i n accordance w i t h recommendations of Dr. G. G. E. Scudder.  The larvae were l a i d on the s l i d e s on  t h e i r r i g h t side so that the body between the a n t e r i o r and p o s t e r i o r sacs was extended f u l l y , but not stretched.  Thirty  to s i x t y larvae were placed on a standard microscope s l i d e and covered f i r m l y w i t h a cover s l i p almost equal i n dimensions to the s l i d e before adding water. The larvae were i d e n t i f i e d to species using the key of Cook (1956).  Separation of the three species present were  based on the presence and l o c a t i o n of an antenna! spine, shape of the p r e l a b r a l appendage, and p o s i t i o n of the basal mandibular tooth. A Wisconsin plankton net having an upper r i n g diameter of 23 cm and f i t t e d with No. 10 nylon net was used i n 1963 to study the h o r i z o n t a l d i s t r i b u t i o n of the Chaoborus larvae i n the l i m n e t i c zone.  Ten t o t a l v e r t i c a l hauls were made each  month (June-September) at ten randomly selected s t a t i o n s where the depth was about 14 m. formalin solution.  Samples were preserved i n 10$  A l l larvae were counted i n each sample*  A.test of randomness (Kutkuhn, 1958) was used t o determine the type of h o r i z o n t a l d i s t r i b u t i o n c h a r a c t e r i s t i c of the  9 larvae during the summer.  Part 2. Laboratory Studies. Experiments were c a r r i e d out at Cprbett Lake i n a darkroom (3 x 3 x 3 m) having a wooden frame covered with black polyethylene sheets ( P i g . 2A).. Two p l a s t i c tubes (2 m length, 14.5 cm i n s i d e diameter and 3.2 mm t h i c k w a l l ) marked o f f i n 20 cm depth i n t e r v a l s were placed i n s i d e on a table so that t h e i r tops (open ends) j u s t protruded out through holes made i n the roof ( F i g . 2B).  This arrangement made i t p o s s i b l e t o  study the migration under n a t u r a l and c o n t r o l l e d l i g h t c o n d i t i o n s . Two shutters made from furnace vents were used to a l t e r the l i g h t i n t e n s i t y over the tubes.  A sheet of wax paper was  placed i n s i d e each shutter to d i f f u s e the incoming  light.  Usually one l i g h t shutter was f i t t e d over the top of the tube, while the other was placed over the search u n i t of the photometer. Two l i g h t recorders were used u s u a l l y i n each  experiment.  The "deck" c e l l of the submarine photometer (Model 15-M-02/1G.M. Manufacturing Co.) was placed on the roof of the dark room, while the "sea" c e l l was used inside to record the l i g h t gradient along the p l a s t i c tube.  A Photovolt (Model 514 M)  photometer f i t t e d with phototube C and n e u t r a l density f i l t e r s was placed on the ground about 15 m from the dark room to obtain l i g h t readings.  The l i g h t i n t e n s i t y recorded by the  photometer a t ground l e v e l was assumed to represent that a t the surface of the tubes.  When the surface l i g h t over the  experimental tubes was changed with the shutter apparatus,  10 i t was measured at ground l e v e l w i t h the Photovolt photometer whose search u n i t was covered w i t h the other shutter having the same degree of closure. The thermistor described p r e v i o u s l y was used to record temperature at every 10 cm depth i n t e r v a l i n the tube. Unfortuna t e l y i t was not possible to c o n t r o l water temperature i n the experimental tubes as the dark room was not i n s u l a t e d and the tops of the tubes were exposed to the outside. The unmodified Winkler Method was used to measure the experimental oxygen conditions.  Usually water samples from  the surface, 100 cm depth and the bottom were analyzed. Lake water f i l t e r e d with a No. 10 net was used i n a l l the experiments. A dim f l a s h l i g h t was used to count l a r v a l d i s t r i b u t i o n i n the tubes at n i g h t . One-hundred f r e s h larvae c o l l e c t e d from desired depths of the lake w i t h the Clarke-Bumpus sampler were used i n every experiment. D i e l v e r t i c a l migration experiments were attempted i n J u l y , August and September of 1963.  Each experimental 24 hour  s e r i e s consisted of 16 observation periods; every 2 hours during daytime and every hour during dusk and dawn.  Each  observation consisted of counting l a r v a l d i s t r i b u t i o n f o r every 20 cm depth i n t e r v a l , measuring l i g h t i n t e n s i t y ( i f necessary^, and recording water temperature. Water samples were taken at the end of each experiment. preserved i n 10$ formalin s o l u t i o n .  Larvae used were  FIGURE 2A.  The darkroom used to study experimentally the d i e l v e r t i c a l migration of Chaoborus f l a v i c a n s larvae.  FIGURE 2B.  Cross s e c t i o n a l view of the darkroom showing the arrangement of the p l a s t i c tubes used to hold the Chaoburus f l a v i c a n s larvae.  12 The importance of l i g h t i n c o n t r o l l i n g v e r t i c a l migration of the larvae was investigated i n August and, September of 1963.  One tube used as a c o n t r o l was exposed to n a t u r a l l y  changing l i g h t conditions, while the other was exposed to a r t i f i c i a l l y changing l i g h t i n t e n s i t i e s .  The experiments  were c a r r i e d out during the period of r e l a t i v e l y constant l i g h t conditions (0900-1800 hours). every 15-30 minutes.  Observations were made  A f t e r recording the l a r v a l d i s t r i b u t i o n  at a given l i g h t l e v e l , the i n t e n s i t y was changed and measured. Temperatures were measured f o r both tubes before and a f t e r each experiment, while water samples were taken only a f t e r f i n i s h i n g the experiment.  Larvae used i n the experiments  were preserved.  RESULTS Part 1.  F i e l d Studies  L a r v a l Size (or Age) Classes Large numbers (about 2878) of larvae were i d e n t i f i e d and measured to the nearest one-tenth mm bladder-bladder length i n order to determine the number and length ranges of l a r v a l size c l a s s e s .  The animals used were taken from samples  c o l l e c t e d i n 1963 during the 1100 hour sampling period of the  June, J u l y , August and September f i e l d s e r i e s .  of small samples (  A l l larvae  60 larvae) were measured and i d e n t i f i e d ,  but only f r a c t i o n s of the large samples were examined. Chaoborus f l a v i c a n s was by f a r the p r i n c i p a l species (96$ of the  larvae sampled), so other species (C. americanus and C.  13 nyblaei) were not considered i n the study* The length frequency data of each month were subjected to p r o b i t a n a l y s i s (Cassie, 1954) to determine o b j e c t i v e l y the means representing size c l a s s e s . These means were then used to c a l c u l a t e the corresponding t h e o r e t i c a l normal curves using the method described by Snedecor (1957).  The points  of overlap between adjacent curves were used to determine the length ranges.  I t was assumed therefore that each c l a s s  would contribute to and gain from the adjacent c l a s s (or classes) s i m i l a r numbers of l a r v a e .  The smallest and l a r g e s t lengths  of each c l a s s were determined f o r each month and were averaged to obtain length ranges of the c l a s s e s . During the summer of 1963 there were 5 size (or age) classes as i n d i c a t e d by v e r t i c a l arrows representing means ( P i g . 3).  A l l 5 occurred on June 17, whereas only 4 were  present during the remainder of the summer.  The f i r s t 4  classes were present on J u l y 20 and August 18, while the l a s t 4 occurred on September 21.  The average bladder to bladder  length ranges of c l a s s 0, 1, 2, 3, and 4 were r e s p e c t i v e l y 0.87-.157, 1.58-2.77, 2.78-4.39, 4.40-6.11 and 6.12-6.51 mm.  The V a l i d i t y of the L a r v a l Size (or Age) Classes as Instars Since an unconventional measuring method (bladder-bladder length) has been used, the question a r i s e s as to whether these size classes represent a c t u a l i n s t a r s .  The number and  length ranges of l a r v a l i n s t a r s have not been determined f o r C. f l a v i c a n s .  MacDonald (1956), using the conventional head  capsule measurement, has e s t a b l i s h e d the existence of four  FIGURE 3.  The length frequency d i s t r i b u t i o n of the Chaoborus f l a v i c a n s larvae c o l l e c t e d during the 1100 hour sampling periods of the 24 hour f i e l d series of June 16-17, J u l y 20-21, August 17-18 and September 21-22, 1963. The v e r t i c a l arrows indicate means, while the v e r t i c a l bars mark the points of overlap of the calculated t h e o r e t i c a l normal curves.  14  15 i n s t a r s f o r two t r o p i c a l species, C. anomalus and C. species B. Deonier (1943), using another recognized method (modificat i o n of the mouth parts and anal f i n ) , has established four i n s t a r s f o r C. astictopus of Clear Lake, C a l i f o r n i a .  He  also mentions that the overwintering larvae of the Clear Lake gnat are s i g n i f i c a n t l y l a r g e r than those of the l a s t i n s t a r ; an observation s i m i l a r to that made by Muttkowski C. punctipennis of Lake Mendota, Wisconsin.  (1918)for  I t appears therefore  that temperate Chaoborus larvae can develop through f i v e i n s t a r s which may be represented by f i v e l a r v a l age (or s i z e ) groups based on the body length measurement. As the average t o t a l length measurement of c l a s s 0 larvae (determined by bladder-bladder  length measurement) i s s i m i l a r  to that (about 1.75 mm average length) of newly hatched C. flavicans  larvae measured by Berg (1937), l a r v a l c l a s s 0  must represent the f i r s t i n s t a r .  S i m i l a r l y the average t o t a l  lengths of c l a s s 3 and 4 larvae were s i m i l a r to those (10.8 and 11.2 mm mean length) of two oldest l a r v a l groups ever encountered by Berg i n Esrom Lake, Denmark. As Berg states that larvae having 11.2 mm mean length overwintered,  they  might represent a f i f t h i n s t a r , thus making the f o u r t h l a r v a l c l a s s of Corbett Lake equivalent to the f i f t h  instar.  By  s i m i l a r reasoning the t h i r d l a r v a l c l a s s present i n Corbett Lake may be considered the f o u r t h i n s t a r .  Therefore the  seasonal changes i n abundance of the l a r v a l age groups may be a t t r i b u t e d to animals undergoing i n s t a r changes.  16 Abundance of L a r v a l Groups and t h e i r Daytime V e r t i c a l D i s t r i b u t i o n The data used to determine the numbers and average ranges of the size (or age) classes were analyzed i n greater d e t a i l to show the abundance and daytime v e r t i c a l d i s t r i b u t i o n of the l a r v a l groups on a d i e l and seasonal b a s i s .  Larval  fragments having heads were t o t a l l e d , and appropriate numbers of them were a l l o t t e d to each c l a s s .  A l l larvae encountered  were assumed to be C. f l a v i c a n s as the i n c l u s i o n of very few of the other species would not a f f e c t the r e s u l t s f o r the major species.  The abundance of larvae at each sampling depth  were expressed i n numbers per 100 1; the a c t u a l or estimated t o t a l counts were divided by the volume of water supposedly passed through the sampler during each tow.  Confidence l i m i t s  were c a l c u l a t e d f o r a l l t o t a l estimated counts (Appendices V, VI, VII and V I I I ) . The r e l a t i v e abundance of larvae i n each c l a s s changed w i t h the progression of summer i n 1963  (Fig. 4).  Class 0  and 1 larvae, having t h e i r greatest abundance i n June, decreased markedly i n numbers u n t i l v i r t u a l l y none were present by September.  Class 2 animals decreased s l i g h t l y seasonally,  while the c l a s s 3 larvae increased i n abundance.  The  few  c l a s s 4 larvae became s l i g h t l y more abundant by September. There were marked d i f f e r e n c e s i n the v e r t i c a l d i s t r i b u t i o n of larvae with respect to size during the daytime ( F i g . 4 ) . The majority of the c l a s s 0 and 1 larvae inhabited the surface to 8 m zone (the warmer, oxygenated e p i - and metalimnion) during the e n t i r e summer, while the few c l a s s 4 larvae occupied  17 the 8 to 13 m region.  Conversely the c l a s s 2 and 3 larvae  underwent marked seasonal changes i n daytime v e r t i c a l distribution. The c l a s s 2 animals occuppied the surface to 12 m zone on June 17 and J u l y 20 with maximum density occurring a t 3 m i n June and somewhat i n J u l y ( F i g . 4 ) .  In contrast most of  them inhabited the 7 to 12 m region on August 18 and September 21 with greatest abundance a t about 10 m on both occasions. The c l a s s 3 larvae showed a trend s i m i l a r to that of c l a s s 2 animals ( F i g . 4 ) .  They occuppied the surface to 12 m  zone on June 17 with maximum density occurring a t about 11 m. In contrast most of the c l a s s 3 larvae inhabited the 7 to 13 m (or perhaps deeper) region on J u l y 20, August 18, and September 21 with greatest abundance being a t about 10.5 m. The seasonal s h i f t i n daytime v e r t i c a l d i s t r i b u t i o n of c l a s s 2 and 3 larvae was not c o r r e l a t e d to changes i n l i g h t penetration.  The depth a t which l i g h t could no longer be  measured w i t h the submarine photometer remained at about 15— 16 m during the 4 months.  Seasonal V a r i a t i o n i n Horizontal D i s t r i b u t i o n Because the a n a l y s i s of t r i p l i c a t e samples taken at each of several depths i n 1962 (August 12) and 1963 (June 16) revealed that the Chaoborus larvae might have a clumped h o r i z o n t a l d i s t r i b u t i o n , a sampling design of Ricker (1938) was used during the summer of 1963 to study t h i s aspect more extensively.  Ten t o t a l v e r t i c a l hauls were taken during the  FIGURE 4.  The daytime v e r t i c a l d i s t r i b u t i o n and r e l a t i v e abundance of the l a r v a l classes of C. f l a v i c a n s i n Corbett Lake based on samples coTlected during the 1100 hour sampling periods of the 24 hour f i e l d s e r i e s of June 16-17, J u l y 20-21, August 17-18 and September 21-22, 1963; oxygen and temperature conditions are also shown f o r each p e r i o d .  NO IQO  2 0 0  PER  IOO L  O  TEMP  I O O 2  ? °  3  , '  7  3  ?  AND OXYGEN 10  « P P M ° -  7  20  NO 100  PER  IOOL  200  O  I O O  j /" / . 2  /  o  '  /  .''  / ' T E M P  \ JUNE °c  I O O  O  o  10  20  100  2 0 0  I O O  2 0 0  O  2 0 0  O  I O O  P P M  1  / ' ' T E M P  •I CLASS 100  O  CLASS O  JULY  I  IOO  C S  10  O  CLASS 20  IOO  O  2  2 7 6  CLASS 3 0 O  O  I O O  O  I O O  3  CLASS  P P M  Si 4 L  / / T E M P  /  AUGUST O  I O O  4  c  10  20  P P M  SEPTEMBER  \ I O O  2 0 0  200  IOO  4  19 l a t e afternoon or e a r l y evening of each month (1942-1636 hours on June 16, 1835-1830 hours on J u l y 20, 1903-1955 hours on August 17 and 1738-1836 hours on September 21).  The variance  over mean r a t i o value of 1,88 c a l c u l a t e d w i t h the method of Kutkuhn (1958) was used to determine whether the larvae showed a clumped (negative-binomial) or random (Poisson) distribution. The variance over the mean r a t i o c a l c u l a t e d from the sampling data revealed that the larvae had a clumped h o r i z o n t a l d i s t r i b u t i o n on each sampling!;.day, but the degree of clumping increased during the summer (Table 1).  The r e s u l t s may  i n d i c a t e a seasonal increase i n the aggregation behavior of the l a r v a e .  D i f f e r e n t i a l Migratory Behavior of the L a r v a l Classes Samples c o l l e c t e d during the 1100, 2100 and 0500 hour sampling periods of the monthly 24 hour f i e l d s e r i e s (June 17-18, J u l y 20-21, August 18-19 and September 21-22) of 1963 were used to study behavior of the d i f f e r e n t l a r v a l c l a s s e s . As 1100, 2000 and 0500 hour periods were chosen to represent times of daytime d i s t r i b u t i o n , maximum ascent (except i n September) and maximum descent r e s p e c t i v e l y , any s u b s t a n t i a l migration undergone by a l a r v a l class would be detected i n samples taken during these periods;  The confidence l i m i t s  of estimated t o t a l counts were c a l c u l a t e d (Appendices V, V I , VII and V I I I ) . The younger larvae (class 0 and l ) underwent v i r t u a l l y  20 TABLE I . Comparison of the monthly t o t a l v e r t i c a l hauls taken during l a t e afternoon or e a r l y evening at randomly selected s t a t i o n s w i t h No. 10 Wisconsin net at Corbett Lake i n 1963. Haul No. 1 2 3 4 5 6 7 8 9 10 Total Mean (x) Sum of Squares Variance (S )  June 16  J u l y 20  August 17  418 422 436 480 433 447 442 356 459 447  251 235 271 167 220 298 297 298 294 249  199 205 210 108 139 234 292 156 165 155  167 145 214 232 124 137 95 85 111 121  2580 258 16570 1841 7.14 64.22 0.005  1863 186.3 25240 2804 15.08 135.48 0.005  1431 143.1 21115 2347 16.4] 147.5! 0.005  4340 434 9632 1070 2.41 22.19 P r o b a b i l i t y (p.) 0.01-0.005  September  21 no d i e l migration, while the older ones ( c l a s s 2, 3 and showed marked d i e l movements (Pigs. 5 and 6). 0 and 1 larvae present on August 18-19  4)  The few c l a s s  showed p r a c t i c a l l y no  migration; these larvae were v i r t u a l l y absent i n September. Although only few c l a s s 4 larvae were present, they neverthel e s s showed a marked d i e l v e r t i c a l migration each month. There appeared also to be a seasonal trend of p r o g r e s s i v e l y fewer older larvae ( c l a s s 2, 3 and 4) undergoing ascent ( F i g s . 5 and 6).  The trend was p a r t i c u l a r i t y evident f o r c l a s s 3  and 4 animals.  V i r t u a l l y a l l the c l a s s 3 larvae i n h a b i t i n g  the 8-13 m zone during the daytime ascended on the 2100 hour period of June 17 and J u l y 20.  About 80$ of the c l a s s 3 animals  moved up on the 2100 hour period of August 18, while only about 60$ of the larvae ascended on t h i s period of September 21. S i m i l a r i l y p r a c t i c a l l y a l l the c l a s s 4 larvae occupying the 11 to 13 m depths during the daytime ascended during the  2100  hour period of June 17 and J u l y 20, while fewer of these larvae moved up on the same time period of August 18 and September 19.  The discrepancy i n the abundance of c l a s s 2  and 3 larvae present during the 1100 and 2100 hour periods i s probably due to ascent of larvae which inhabited depths below 13 m during the day time.  The trend may be c o r r e l a t e d  to seasonal increase i n rate of l i g h t i n t e n s i t y change at dusk as i n d i c a t e d by the isolumes p l o t t e d i n Figure 9. can be seen that the isolumes (.1, 1.0, 10 and 100  It  luxes)  disappear on June 17 and J u l y 20 (1920-2110 hours) at much slower rate than do those on August 18 (1920-2110 hours)  FIGURE 5.  The v e r t i c a l d i s t r i b u t i o n of c l a s s 0, 1, 2, 3 and 4 larvae of C. f l a v i c a n s i n Corbett Lake during the 1100, 2100 and 0500 hour periods of the June 16-17 and J u l y 20-21 s e r i e s , 1963.  IIOO  JUNE 17-18 1963 2IOO  N O . / l O O L. O  IOO  IIOO  O 5 0 0  -  CLASS  JULY 20-21 1963 2IOO  0 5 0 0 :  •  1  O  12 O 4  1  CLASS  8 12  CLASS  2  CLASS  3  CLASS  4  Or 4  :  8• 12  :  IIOO  2IOO  0 5 0 0  IIOO PACIFIC S T A N D A R D TIME  2IOO  0 5 0 0  FIGURE 6.  The v e r t i c a l d i s t r i b u t i o n of c l a s s 0, l 2, 3 and 4 larvae of C. f l a v i c a n s i n Corbett Lake during the 1100, 2100 and 0500 hour periods of the August 17-18 and September 21-22 s e r i e s , 1963. f  DEPTH io  co  O  to  oo  O  to  IN oo  D E P T H IN  tz  METRES -fc-O  METRES  ru  oo  A  O  io  oo  -b.  O  24 and September 21 (1520-1920 hours). Furthermore the c l a s s 2 and 3 larvae ( e s p e c i a l l y c l a s s 2) appeared to show a seasonal trend f o r completion of descent to occur p r o g r e s s i v e l y e a r l i e r ( F i g s . 5 and 6).  About 30-  40$ of the c l a s s 2 larvae occupying the upper 4 metres during the 2100 hour period of June 17 and J u l y 20 descended to lower depths by 0500 period of the f o l l o w i n g days (June 18 and J u l y 21).  In contrast about 60-70$ of the c l a s s 2 animals  i n h a b i t i n g the upper 4 metres during the 2100 hour period of August 18 and September 21 moved down to lower l a y e r s by 0500 period of the f o l l o w i n g days.  This trend may be due to  darkness occurring p r o g r e s s i v e l y e a r l i e r .  Migration Pattern of the Older Larvae Samples c o l l e c t e d during the 0800, 1100,  1530,  1930,  2130, 2330, 0330 and 0510 hour sampling periods of the September 21-22  s e r i e s of 1963 were used to compare the migra-  tory pattern of the o l f e r larvae (Class 2, 3 and 4) on a d i e l basis.  Samples taken during the other s e r i e s (June 17-  18, J u l y 20-21  and August 18-19) were not used, as i t was  v i r t u a l l y impossible to measure and count a l l the larvae i n the subsamples or i n samples c o l l e c t e d during the 4 s e r i e s . Confidence l i m i t s were c a l c u l a t e d f o r the estimated counts (Appendix V I I I ) . Comparison of the d i s t r i b u t i o n patterns f o r 1930,  2130  and 2330 hours ( F i g . 7) i n d i c a t e d that the three l a r v a l classes had approximately  s i m i l a r timing of ascent and descent.  In  25 general the migratory pattern of the three l a r v a l classes appeared s u f f i c i e n t l y s i m i l a r to consider them as a s i n g l e migrating group. Furthermore the migration may be s p l i t i n t o four phases: 1) day-depth, 2) ascent from the day-depth to the surface, 3) descent from the surface, 4) a more r a p i d descent during dawn (when s u n l i g h t s t a r t s t o penetrate the water) ( F i g , 7 ) , In September the f i r s t phase l a s t e d from about 0800 to s l i g h t l y before 1930 hours.  The second phase began about  (or before) 1930 hours (dusk) and l a s t e d u n t i l about 2130 hours.  The t h i r d phase commenced a t about 2130 hours and  terminated a t sometime before 0510 hours when s u n l i g h t s t a r t e d to penetrate the water; t h i s phase occurred therefore during darkness.  The f o u r t h phase s t a r t e d at about 0510 hours (dawn);  lack of l i g h t and d i s t r i b u t i o n data a f t e r t h i s time made i t impossible to determine the termination of f o u r t h phase. The d i e l v e r t i c a l migration seemed therefore to be c o r r e l a t e d with d i e l changes i n subsurface l i g h t i n t e n s i t y . Since the 3 l a r v a l classes probably behaved as a s i n g l e migrating group ( F i g . 7) during the e n t i r e summer, counts of larvae i n samples c o l l e c t e d during the monthly s e r i e s were made i n order to study seasonal changes i n d i e l v e r t i c a l migration of the c l a s s 2, 3 and 4 l a r v a e .  Changes i n d i s t r i b u t i o n  patterns f o r the sampling periods during the monthly 24-hour s e r i e s were a t t r i b u t e d therefore to the movements of the older larvae ( c l a s s 2, 3 and 4 ) , as younger (class 0 and l ) larvae underwent v i r t u a l l y no v e r t i c a l migration.  Confidence l i m i t s  FIGURE 7.  The d i e l v e r t i c a l migration of c l a s s 2, 3 and 4 larvae of C. f l a v i c a n s during September 12-22 s e r i e s of 1963. The broken l i n e s represent the 14.8°, 12° and 6° C isotherms; the s o l i d l i n e s represent the 1.0 l u x isolume.  27 were c a l c u l a t e d f o r the estimated t o t a l counts  (Appendices  IX, X and X I ) . The d i e l v e r t i c a l migration of the 3 l a r v a l classes showed a seasonal change apparently c o r r e l a t e d w i t h seasonal changes i n timing of subsurface l i g h t e x t i n c t i o n (at dusk) and of subsurface l i g h t penetration (at dawn) ( F i g . 8 ) . The comparison of the d i s t r i b u t i o n patterns of the 1520 and 1920 hour sampling periods showed that the termination of day-depth phase occurred p r o g r e s s i v e l y e a r l i e r ( F i g . 8 ) . The phase terminated very s h o r t l y before 1920 hours during the June 16-17 and J u l y 20-21 s e r i e s .  This was i n f e r r e d from  the f a c t that the 1920 hour d i s t r i b u t i o n pattern indicated very s l i g h t ascent over the previous d i s t r i b u t i o n p a t t e r n . The phase ended s h o r t l y before 1920 hours during the August 18-19  s e r i e s , as the 1920 hour d i s t r i b u t i o n pattern showed  s u b s t a n t i a l ascent over the 1520 hour p a t t e r n .  The day-depth  phase ended w e l l before 1920 hours during the September 21-22 s e r i e s as the 1920 hour d i s t r i b u t i o n pattern may represent maximum ascent. Comparison of the d i s t r i b u t i o n patterns f o r 1920, 2110 and 2310 hours showed s i m i l a r seasonal changes f o r the second phase (ascent from the day depth to the surface) of d i e l v e r t i c a l migration ( F i g . 8).  The phase commenced a t about  1920 hours and ended a t about 2110 hours during the June, J u l y and August s e r i e s .  I t could not have terminated a t  about 2310 hours during these s e r i e s as the comparison i n d i c a t e d the descent to be w e l l under way by 2310 hours.  In contrast  FIGURE 8.  The d i e ! v e r t i c a l migration of the C. f l a v i c a n s larvae i n Corbett Lake curing June T6-17, J u l y 20-21, August 17-18 and September 21-22 s e r i e s , 1963. Surface temperature and 10°, 5°, 4° and 3.5° C temperature depths are shown. The 0.1, 1, 10 and 100 l u x isolumes are i n d i c a t e d w i t h solid lines*  NO PER i  O  O8OO  II20  IS20  1920  1  IOOL  2 0 0  1  4 0 0  21 IO PACIFIC  STANDARD  23IO TIME  0320  0510  29 the phase began w e l l before 1920 hours and ended s h o r t l y a f t e r 1920 hours during the -September s e r i e s .  The comparison  of the 1920 and 2110 hour d i s t r i b u t i o n patterns i n d i c a t e d the descent to be w e l l under way by 2110 hours. Comparison of the d i s t r i b u t i o n patterns f o r 1920, 2110, 2310, 0320 and 0510 hours i n d i c a t e d that the t h i r d phase (descent from surface) became progressively longer and appeared c o r r e l a t e d with changes i n the duration of t o t a l darkness (Pig.  8 ) . The phase commenced sometime at about 2110 hours  and ended at about 0320 during the June, J u l y and August series.  I t started s h o r t l y a f t e r 1920 hours ( f o r reasons  described p r e v i o u s l y ) and ended at about 0510 hours during the September s e r i e s . The f o u r t h phase (a r a p i d descent during dawn) commenced at about 0510 hours during June, J u l y and August series and sometime a f t e r 0510 hours during September series ( P i g . 8 ) . The l i g h t conditions (time when l i g h t f i r s t penetrated the water and the depths of the 0.1, 1.0, 10, 100 l u x isolumes) during the June, J u l y and August series were s i m i l a r .  The  time at which the l i g h t f i r s t penetrated the water during the September s e r i e s was s i g n i f i c a n t l y l a t e r than those of the previous s e r i e s . Other Aspects of the D i e l V e r t i c a l Migration In 1962 echo traces were taken about every 15 minutes during the dusk and dawn periods of October 1-2 at Crosssection A ( P i g . l ) using constant gain (volume c o n t r o l of  30 the echo sounder) and boat speed. The traces revealed some i n t e r e s t i n g aspects on the d i e l v e r t i c a l migration of the l a r v a l population i n r e l a t i o n to the lake basin ( F i g . 9 ) . In the daytime (1630 and 1745 hour echo traces) the periphery of the Chaoborus s c a t t e r i n g layer appeared to be i n contact w i t h the lake basin and was thinnest at these regions.  During the ascent (1800-1915 hour traces)  the l a y e r ( l a r g e l y Chaoborus larvae) expanded s l i g h t l y shoreward, but appeared to have l i t t l e contact with the shore.  The c l e a r  spots over the shore region can be seen on the 1805, 1830, 1845, 1900 and 1915 traces, and p a r t i c u l a r l y w e l l on the 1815 hour trace when background noise was minimal.  In contrast  the layer became more d i f f u s e and appeared i n contact with the shores during descent (0445-0645 hour t r a c e s ) . The echo traces were also used to c a l c u l a t e the rates of ascent and descent of the larvae ( F i g . 9 ) . As the larvae occupying the bottom p o r t i o n of the s c a t t e r i n g l a y e r appeared to ascend f i r s t (compare 1800, 1805 and 1815 hour echo t r a c e s ) , i t was assumed that these larvae moved up to the surface and descended to the o r i g i n a l daytime depth of 12.5 m ( F i g . 10). As the ascent commenced between 1745 and 1800 hours, i t was decided a r b i t r a r i l y to have occurred p r e c i s e l y a t 1750 hours. As f u r t h e r a n a l y s i s of these and other traces suggested that the termination of ascent occurred when the "residue" layer ( i n d i c a t e d by arrows) was thinnest (compare 1800-1915 hour echo t r a c e s ) , the end of ascent was decided to have occurred at 1845 hours.  Since the thickening of the "residue" layer  FIGURE 9»  Echo sounding traces across Corbett Lake at Cross Section A, October 1-2, 1962 (differences i n length of trace caused byv a r i a t i o n i n length of run or boat speed; background noise may be ignored). The arrows i n d i c a t e the "residue" l a y e r . Time expressed i n hundred hours ( P a c i f i c Standard Time).  DEPTH IN METRES  32 i n d i c a t e d descent, the onset of descent probably occurred at about 1900 hours (compare 1900-0645 echo t r a c e s ) .  The  descent terminated a t 0745, the time at which the thickness of the s c a t t e r i n g layer f i r s t became constant.  Consequently  the ascent period l a s t e d 55 minutes (1750-1845), while the descent phase involved 705 minutes (1900-0645).  Therefore  the rates of ascent and descent were 13.6 and 1.1 m/hour respectively.  Part 2. Laboratory Studies D i e l V e r t i c a l Migration under Experimental Conditions Several 24 hour laboratory experiments were c a r r i e d out during the summer of 1963 to study the d i f f e r e n t i a l migratory behavior of the older l a r v a l classes (only c l a s s 2, 3 and 4 larvae migrated). A s e r i e s was done on J u l y 16-17 with 100 larvae (4.80 mm mean length) c o l l e c t e d from about the 13 m depth of the lake.  Two s e r i e s were c a r r i e d out simultaneously  on August 13-14 with 100 larvae batches (3.30 mm mean length f o r both) taken from the surface and about the 5 m depth of the lake.  On August 16-17 two 100 larvae batches (3.80 and  5.20 mm mean length) c o l l e c t e d from 10 and 14 m depth r e s p e c t i v e l y were used.  F i n a l l y two series were c a r r i e d out  on September 13-14 w i t h larvae batches (4.32 and 5.32 mm mean length) c o l l e c t e d from about 10 and 14 m depths i n order to r e p l i c a t e the r e s u l t s of August 16-17.  ( I t was not possible  to r e p l i c a t e the r e s u l t s of August 13-14 Series i n September as comparable s i z e d larvae were not present i n the l a k e ) .  33 The experiments were not s t a r t e d u n t i l the larvae appeared quiescent ( l a c k of d a r t i n g movements). The majority of the larvae used on J u l y 16-17, August 13-14, August 16-17 and September 13-14 belonged r e s p e c t i v e l y to classes 3, 2, 2 and 3, and 2 and 3. No experiments were conducted with the class 0 and 1 larvae, as they were too small to be observed r e a d i l y i n the tubes.  However i t was f e l t that the c l a s s 2 larvae taken  from the surface and 5 m depth of the lake would give r e s u l t s since they both had a s i m i l a r daytime v e r t i c a l d i s t r i b u t i o n i n the lake. The c l a s s 2 larvae from the surface layer of the lake (0 and 5 m) showed v i r t u a l l y no v e r t i c a l migration i n the experimental tubes ( P i g . 10).  The c l a s s 0 and 1 larvae  underwent p r a c t i c a l l y no migration i n the f i e l d ( F i g s . 5 and 6).  On the other hand c l a s s 2 larvae taken from 10 m i n the  lake during the daytime showed a d i s t i n c t v e r t i c a l migration i n the tubes ( F i g s . 12 and 13); the c l a s s 2 animals underwent d i s t i n c t v e r t i c a l migration i n the f i e l d ( F i g s . 5, 6 and 7 ) . S i m i l a r l y the c l a s s 3 larvae taken from about the 13 and 14 m i n the lake on J u l y 16, August 16 and September underwent  diel  v e r t i c a l migration ( F i g s . 11, 12 and 13); the c l a s s 3 larvae also showed d i s t i n c t d i e l v e r t i c a l migration i n the f i e l d (Figs. 5, 6 and 7 ) . The migratory pattern of the c l a s s 2 larvae i n the tubes was i d e n t i c a l to the f i e l d d i e l movements of the c l a s s 2, 3 and 4 larvae ( F i g s . 12 and 13).  I t consisted of the s i m i l a r  FIGURE 10.  D i e l v e r t i c a l migration of c l a s s 2 larvae ( c o l l e c t e d from the surface and 5 m depth of Corbett Lake) i n adjacent experimental tubes during August 13-14, 1963. Light i n t e n s i t i e s at the surface of both tubes were i d e n t i c a l , as were temperatures at the surface, 100 cm depth and bottom.  I200  I200  1300  1500  1700  1900  1300  1500  1700  1900  2 0 0 0  2 0 0 0  AUGUST 13-14 1963  2IOO  2100  2 2 0 0  2 2 0 0  PACIFIC  2 3 0 0  2 3 0 0  STANDARD  2 4 0 0  0 2 0 0  0 4 3 0  0 5 3 0  0 7 3 0  0 9 0 0  IIOO  2 4 0 0  0 2 0 0  0 4 3 0  0 5 3 0  0 7 3 0  0 9 0 0  IIOO  TIME  FIGURE 11•  D i e l v e r t i c a l migration of c l a s s 3 larvae i n the experimental tube during J u l y 16-17, 1963 at Corbett Lake. Surface l i g h t i n t e n s i t i e s (measured w i t h the submarine photometer) and temperatures at surface, 100 cm depth and bottom of the tube are shown. Probable surface l i g h t i n t e n s i t i e s f o r 1900, 2000 and 2100 hours ( i f Photovolt Photometer was used) are i n d i c a t e d w i t h s o l i d dots j o i n e d with a s o l i d l i n e .  FIGURE 12,  D i e l v e r t i c a l migration of c l a s s 2 and 3 larvae i n adjacent experimental tubes during August 16—17, 1963. L i g h t i n t e n s i t i e s at the surface of both tubes were i d e n t i c a l . a s were temperatures at the surface, 100 cm depth and bottom.  FIGURE 13.  D i e l v e r t i c a l migration of c l a s s 2 and 3 larvae i n adjacent experimental tubes during September 13-14, 1963. L i g h t i n t e n s i t i e s at the surface of both tubes were i d e n t i c a l , a s were temperatures at the surface, 100 cm depth and bottom.  SEPTEMBER  IIOO  1300  1500  1700  1900  2000  2IOO  2200  PACIFIC  13-14 1963  2300  STANDARD  2400  0 2 0 0  0300  0 4 0 0  0 5 0 0  0 7 0 0  0900  TIME -3  38 4 phases:  1) day-depth, 2) ascent from the day-depth to the  surface, 3) descent from the surface a f t e r ascent, 4) a r a p i d descent during dawn period (Pigs. 12 and 13).  There may have  been a morning r i s e a t 0500 hours on September 17 ( P i g . 13). The migratory pattern of the class 3 larvae i n the tubes was not i d e n t i c a l with the f i e l d d i e l movements of the class 2, 3 and 4 larvae (Pigs. 12 and 13).  I t consisted of 5 phases:  1) day-depth, 2) ascent from the day-depth to the surface, 3) descent from the surface, 4) e a r l y morning r i s e to the surface ("dawn r i s e " ) , 5) sharp descent during the dawn period (Figs. 11, 12 and 13).  The e a r l y morning r i s e occurred a t  about 0400 hours on J u l y 17 ( F i g . 11), about 0400-0530 hours on August 17 ( F i g . 12) and perhaps a t about 0500 hours on September ( F i g . 13). The f a i l u r e to depict the morning r i s e i n the f i e l d may. be due to the long time i n t e r v a l between sampling periods (every 2 or 4 hours). In a d d i t i o n the migration cycles of the c l a s s 2 and 3 larvae i n the experimental tubes showed a seasonal change (Figs. 11, 12 and 13), p a r t i c u l a r l y i n the time of maximum ascent.  For the c l a s s 2 larvae maximum ascent was reached  at about 2000 hours i n the August 16-17 series and at about 1900 hours on September 13-14.  The maximum ascent of class  3 larvae occurred a t about 2100 hours i n the J u l y s e r i e s ( F i g . 11), 2000 hours i n the August s e r i e s ( F i g . 12) and 1900 hours i n the September s e r i e s ( F i g . 3 ) . The surface l i g h t i n t e n s i t y was measured during the J u l y  39 s e r i e s with an instrument l e s s s e n s i t i v e than that used during the August and September s e r i e s .  As a r e s u l t the surface  l i g h t i n t e n s i t i e s recorded during the 1900, 2000 and 2100 hours of the J u l y series ( F i g . 11) were corrected to i n t e n s i t i e s which probably would have been recorded with the s e n s i t i v e instrument ( F i g . 11).  Consequently i t was possible to compare  the times of l i g h t e x t i n c t i o n f o r the 3 s e r i e s . The seasonal v a r i a t i o n i n time of maximum ascent appeared to be correlated w i t h changes i n time of surface l i g h t e x t i n c t i o n (Figs. 11, 12 and 13).  During the J u l y series the surface  l i g h t became almost immeasurable a t about 2100 hours, corresponding w i t h the time of maximum ascent of class 3 larvae ( F i g . 11). During the August s e r i e s the surface l i g h t became immeasurable at about 2000 hours, corresponding w i t h the time of maximum ascent f o r class 2 and 3 larvae ( F i g . 12).  During the  September s e r i e s the l i g h t i n t e n s i t y was v i r t u a l l y zero a t about 1900, corresponding with the time of maximum r i s e f o r the class 2 and 3 animals ( F i g . 13). was observed i n the f i e l d .  A s i m i l a r seasonal trend  The maximum ascent was estimated  to have occurred at about 2110 hours during the June, J u l y and August f i e l d series and about 1920 hours during the September f i e l d s e r i e s ( F i g . 8 ) .  Role of Light on D i e l V e r t i c a l M i g r a t i o n Experiments to t e s t f o r exogenous rhythm i n the d i e l v e r t i c a l migration of Chaoborus larvae were c a r r i e d out on August 9 and September 28, 1963 with class 3 larvae c o l l e c t e d  40 f r om the 14 m depth of the lake.  During each experiment two  p l a s t i c tubes were used to hold the animals; the top of one tube was exposed to n a t u r a l l i g h t conditions (control tube), while that of the other was subjected to l i g h t  intensities  regulated by a shutter system previously described.  The  tubes were placed adjacent to each other i n the dark room with a black p l a s t i c sheet separating them. At the beginning and end of each experiment, the c o n t r o l and non-control (or experimental) animals were exposed to i d e n t i c a l l i g h t conditions i n order to evaluate whether the two batches of animals behaved s i m i l a r l y (Figs. 14 and 15). The responses were almost i d e n t i c a l at the s t a r t , but somewhat d i f f e r e n t at the end of the experiments.  Discrepancies between  two sets of n a t u r a l l i g h t readings taken near the conclusion of the experiments were probably due to time lapse between readings (Figs. 14 and 15).  The temperature regimes i n the  c o n t r o l and non-control tubes were v i r t u a l l y i d e n t i c a l during each experiment. I t was possible to induce complete migration c y c l e s , i n c l u d i n g the morning r i s e phase (Figs. 14 and 15). The cycle was induced at a l i g h t i n t e n s i t y range of 3001000 luxes on August 9; i t can be seen that non-control (or experimental) larvae responded very l i t t l e to changes i n l i g h t i n t e n s i t y at a range of 1000-15000 luxes ( F i g . 14). Extremely s l i g h t changes i n l i g h t i n t e n s i t y made the larvae ascend or descend w i t h i n 300-J000 l u x l i g h t range.  The non-control  larvae exposed previously to 1450 luxes (at 1452 hours)  FIGURE 14. The v e r t i c a l movements of c l a s s 3 larvae i n adjacent c o n t r o l (exposed to n a t u r a l l y changing l i g h t conditions) and non-control (exposed to a r t i f i c i a l l y changing l i g h t conditions) experimental tubes on August 9, 1963. I d e n t i c a l temperature conditions i n both tubes; i d e n t i c a l l i g h t i n t e n s i t y over both tubes a t the beginning and end of experiment.  AUGUST 0934  IOIO  1045  II20  1158  1230  1306  1342  9  1963  1416  1452  1528  1600  1646  1718  1756  1830 1905  CONTROL  40h  HI  40  BOh  SO '18.8  \20[ I60  120 160  r  195 I  CONTROL  200h  NON-CONTROL  (NATURALLY  CHANGING)  (APTIFICALLY  H200-  CHANGING)  lOO^  -IIOO 5  20L IOr  J20  OL  40  NON  CONTROL  1  1  _ H40  r  2 U 80h I20t  \60[ I95L  0934  ...ililliliii 1 IO IO  1045  II20  1158  1230  PACIFIC  1306  1342  STANDARD  1416  TIME  1452  1528  h- *  1'° 5 3  ""--V.  Or  x  1600  1646  1718  1756  80  n  l20  ^160  2i.«l|95 1 8 3 0 1905"°  FIGURE 15. The v e r t i c a l movements of c l a s s 3 larvae i n adjacent c o n t r o l (exposed to n a t u r a l l y changing l i g h t conditions) and non-control (exposed to a r t i f i c i a l l y changing l i g h t c o n d i t i o n s ) experimental tubes on September 28, 1963. I d e n t i c a l temperature conditions i n both tubes; i d e n t i c a l l i g h t i n t e n s i t y over both tubes a t the beginning and end of experiment.  SEPTEMBER  PACIFIC  2 8 1963  STANDARD TIME  43 ascended markedly when exposed subsequently 1528 hours).  to 620 luxes (at  The experimental larvae descended only s l i g h t l y  when the l i g h t was lowered to 410 luxes (at 1606 hours), while they moved down markedly when l i g h t was f u r t h e r reduced to 310 luxes (at 1646 hours).  They ascended appreciably upon  exposure to 440 luxes (at 1718 hours) and moved up markedly upon subsequent exposure to 350 luxes (at 1756 hours); these r e s u l t s i n d i c a t e d that the ascent response might be greater at 350 luxes than at 440 luxes. A migration cycle was induced a t a l i g h t i n t e n s i t y range below 100 luxes on September 28; the non-control larvae responded very l i t t l e to changes i n l i g h t i n t e n s i t y above t h i s range ( F i g . 15). The experimental animals exposed p r e v i o u s l y to 60 luxes (at 1710 hours) ascended markedly when l i g h t i n t e n s i t y was reduced to 5 luxes (at 1740 hours).  The larvae  descended sharply i n the absence of l i g h t (at 1810 hours), while they ascended upon subsequent exposure to 0.3 l u x .  DISCUSSION Seasonal V a r i a t i o n i n H o r i z o n t a l D i s t r i b u t i o n During the summer of 1963,: the larvae had a clumped h o r i z o n t a l d i s t r i b u t i o n which increased w i t h the progression of summer (Table l ) .  The s i g n i f i c a n c e of t h i s r e s u l t can be  speculated upon by the consideration of the seasonal change i n dominant size classes (or i n s t a r s ) .  There was a progressive  decrease i n the abundance of class 0 and 1 larvae which d i d not migrate and were l a r g e l y confined to the epilimnion ( F i g s .  44 4, 5 and 6).  These young larvae are the l e a s t s t r u c t u r a l l y  d i f f e r e n t i a t e d ( f o r example, the muscles are poorly developed) of larvae present.  In f a c t they may be so undeveloped  s t r u c t u r a l l y that they are t r u l y planktonic with l i t t l e or no c o n t r o l over movement and are therefore d i s t r i b u t e d w i t h i n the eplimnion s o l e l y by the s l i g h t water currents i n Corbett Lake.  I t may be expected therefore that such animals are  randomly d i s t r i b u t e d .  Conversely  the c l a s s 2, 3 and 4 larvae  w i l l be more developed with respect to structure (greater m o b i l i t y ) , physiology and p o s s i b l y behavior.  I t i s possible  that these older larvae are clumped i n d i s t r i b u t i o n .  There-  fore the h o r i z o n t a l d i s t r i b u t i o n of the t o t a l l a r v a l population appears l e a s t clumped i n June probably owing to the  modifying  influence of large numbers of randomly d i s t r i b u t e d small larvae, while i t i s most clumped i n September because there are v i r t u a l l y no c l a s s 0 and 1 larvae present.  The E f f e c t of Age and Environmental Factors on V e r t i c a l Distribution During the daytime (1100 hours) the small larvae  occupied  the oxygen r i c h epilimnion (above 8 m) of Corbett Lake, while l a r g e r and older ( c l a s s 2, 3 and 4) inhabited the but not the bottom mud  hypolimnion,  ( F i g . 4).  A nearly t o t a l l y l i m n e t i c summer population of Chaoborus larvae showing t h i s s i z e c h a r a c t e r i s t i c has been observed only on rare occasions.  Dendy (1956) has observed such a summer  population, but d i d not determine whether the larvae were  45 v e r t i c a l l y s t r a t i f i e d according to size during the daytime. Hunt (1958), i n v e s t i g a t i n g a deep F l o r i d a lake, has found a t o t a l l y limnetic population whose larvae increased i n s i z e with increase i n depth.  S i m i l a r l y Worthington and Ricardo  (1936), sampling Lake Edward i n A f r i c a , have found a s t r i c t l y l i m n e t i c population whose larvae are v e r t i c a l l y d i s t r i b u t e d with respect to s i z e .  The lakes containing such l a r v a l popula-  t i o n s have common chemical c h a r a c t e r i s t i c s ; the lower layers of the lakes are severely depleted of oxygen and contain detectable traces of ^ S . In most lakes containing l a r v a l populations, the larvae are v e r t i c a l l y d i s t r i b u t e d according to size during the daytime, but with the older larvae being benthic (Muttkowski, 1918; Rawson, 1930; Eggleton, 1932; Berg, 1937; M i l l e r , 1941; MacDonald, 1956; Wood, 1956; Woodmanse and Grantham, 1961).  It is  noteworthy that these lakes containing daytime benthic larvae have no ^ S i n t h e i r lower l a y e r s . I t seems therefore that h i g h l y reduced mud may d i r e c t l y or i n d i r e c t l y prevent the larvae from entering the bottom of productive lakes during the daytime.  The f a c t that larvae  enter the bottom mud of Corbett Lake a f t e r f a l l supports t h i s speculation.  overturn  In a d d i t i o n i t may be that l i g h t  detectable by the larvae does not penetrate to the bottom i n such supposedly productive lakes, therefore not n e c e s s i t a t i n g the animals to enter the bottom mud. Studies done on both freshwater and marine crustacean plankters i n d i c a t e s i m i l a r size (or age) and depth r e l a t i o n s h i p s .  46 Gardiner (1933), working with Galanus fimarchius i n the North Sea, has shown that copepbdite stages 3 and 4 l i v e i n the upper layers and stages 5 and 6 i n the deep waters.  Langford (1938)  have shown that the young stages of a freshwater cladoceran Daphnia l o n g i s p i n a remain above the thermocline i n Lake N i p i s s i n g during daytime, while the adults remain below i t .  The E f f e c t of Age and Environmental Factors on the D i e l Vertical Migration The c l a s s 0 and 1 (or f i r s t and second i n s t a r ) larvae underwent p r a c t i c a l l y no d i e l v e r t i c a l migration i n Corbett Lake while the class 2, 3 and 4 (or r e s p e c t i v e l y t h i r d , f o u r t h and f i f t h i n s t a r ) larvae d i d (Figs. 5 and 6).  The experimental  r e s u l t s seem t o corroborate the f i e l d observations; c l a s s 2 larvae taken from the upper layers (0 and 5 m) of the lake were assumed to react s i m i l a r l y inasmuch as class 0 and 1 larvae showed v i r t u a l l y no v e r t i c a l movements, while c l a s s 2, 3 and 4 animals taken from the lower depths (10-14 m) made obvious migrations (Figs. 10, 11, 12 and 13). Dendy (1956), describing the presence of t o t a l l y  limnetic  l a r v a l population i n some lakes, do not c i t e the existence of d i f f e r e n t i a l migration a b i l i t y between l a r v a l groups.  In  contrast, others (Juday, 1921; Berg, 1937; Wood, 1956; Hamilton, 1961; Woodmanse and Grantham, 1961) have observed both benthic and l i m n e t i c d i s t r i b u t i o n s of larvae, but found i n v a r i a b l y that both younger and older animals underwent a d i s t i n c t v e r t i c a l migration. However they f a i l to specify the size  47 ranges of the younger and older larvae.  Nevertheless Berg  (1937) has shown experimentally that young larvae (1.7 mm mean length) do not migrate v e r t i c a l l y .  N i c h o l l s (1934),  working w i t h Calanus i n the Clyde area, has noted that the n a u p l i a occur above 30 m and do not undergo d i e l changes i n d i s t r i b u t i o n , while the copepodite stages 1, 2, 3 and 4 undergo v e r t i c a l migration ( e s p e c i a l l y stage 4 ) .  In contrast  he has found the stage 5 animals to be unresponsive. As a consequence of d i f f e r e n t i a l migratory behavior between l a r v a l groups of Chaoborus, the younger larvae (class 0 and 1) remained i n the warmer oxygenated e p i l i m n i o n throughout the e n t i r e day, whereas the older animals (class 2, 3 and 4) encountered both the e p i l i m n i o n and colder deoxygenated hypolimnion during the 24 hour period (Pigs. 4, 5 and 6 ) . These observations suggest that there may be several f a c t o r s which may account f o r the d i f f e r e n t i a l migration. The smaller larvae may have a much narrower temperature and oxygen range than the older ones.  However i t remains to be  demonstrated whether d i f f e r e n c e s i n p h y s i o l o g i c a l tolerance of these f a c t o r s e x i s t between the two sets of larvae, and whether or not these may a c t u a l l y a f f e c t migration. More l i k e l y the extent of p h y s i o l o g i c a l and morphological development of p e r t i n e n t structures (muscles, sense organs and a i r bladder) i s of greater importance.  Deonier (1943), working with Chaoborus  a s t i c t o p u s , has shown that the simple eye i s present i n a l l i n s t a r s , while the compound eye appears i n the t h i r d i n s t a r (comparable to class 2 of t h i s study) and are developed f u l l y  48 i n the f o u r t h i n s t a r (comparable to c l a s s 3).  Therefore i t  may be that the compound eyes (regardless of degree of development) are a v i t a l sense organ f o r v e r t i c a l migration, providing that l i g h t i s the c o n t r o l l i n g f a c t o r .  Berg (1937) has observed  the a i r sacs to become f i l l e d with a i r before the C. f l a v i c a n s larvae hatch, while Akehurst (1922) has shown the a i r to replace f l u i d i n the a i r bladders s h o r t l y a f t e r hatching.  If  entrance of a i r into the a i r sac i s important i n the hydrostatic functioning of the sac, then i t would seem that the i n a b i l i t y of smaller larvae to migrate can not be a t t r i b u t e d d i r e c t l y to the s t r u c t u r a l and p h y s i o l o g i c a l development of t h i s organ. Hence one must consider now the p o s s i b i l i t y of v e r t i c a l  migration  i n v o l v i n g s t r i c t l y active body movements which implies that the degree of p h y s i o l o g i c a l and s t r u c t u r a l development of the body muscles i s v i t a l l y important.  Although the development  of the body muscles i n the larvae has not been examined, i t may w e l l be that the muscles of younger larvae (class 0 and l ) are not as f u n c t i o n a l as those of older larvae (class 2, 3 and 4). Based on the September samples, there appeared to be no d i f f e r e n t i a l d i e l timing of ascent and descent between migrating l a r v a l groups ( F i g . 7).  Since no one has attempted to separate  the migrating chaoborid larvae into age groups (or i n s t a r s ) , the r e s u l t s can not be compared.  I t i s possible that the time  i n t e r v a l s (every 2 and 4 hours) between sampling periods  are  not short enough to demonstrate the existence of d i f f e r e n t i a l d i e l timing.  However, since the migrating larvae do have a  49 s i m i l a r daytime v e r t i c a l d i s t r i b u t i o n ( i n d i c a t i n g s i m i l a r response to l i g h t c o n d i t i o n s ) , i t seems l i k e l y that they may  have s i m i l a r d i e l timing of ascent and descent.  Fraser  (1938) has found that a l l calyptopis stages of Euphausia superba migrate v e r t i c a l l y and have s i m i l a r timing of upward . and downward migration. The migration cycles observed i n the f i e l d and laboratory d i f f e r e d only with respect to "dawn r i s e " which occurred under experimental  conditions, e s p e c i a l l y f o r c l a s s 3 larvae (Figs.  7, 8, 10, 11, 12 and 13).  Both cycles appeared to be c o r r e l a t e d  to d i e l l y and seasonally changing l i g h t conditions, with the ascent occurring about dusk and the descent taking place during darkness and dawn.  The "dawn r i s e " of the laboratory cycle  occurred during the e a r l y morning hours. The basic migration pattern observed i n Corbett Lake (Figs. 7 and 8) agrees w i t h those of the same or d i f f e r e n t species i n other lakes (Juday, 1921; Eggleton, 1937; 1937; Wood, 1956; Woodmanse and Grantham, 1961). time of maximum ascent (consequently  Berg,  However the  time of descent) -of larvae  i n Corbett Lake does not correspond to those of larvae i n other lakes.  Throughout the summer the maximum ascent occurred  between about 1900-2200 hours i n Corbett Lake. and Eggleton  Juday (1921)  (1931), each working on a d i f f e r e n t lake, found  the maximum r i s e of larvae occurring at about 2200 hours.  In  contrast Woodmanse and Grantham (1961), Berg (1937) and Wood (1956) studying d i f f e r e n t lakes, found the maximum upward movement to take place about 2400 hours.  50 The d e p i c t i o n of "dawn r i s e " i n the experimental but not i n the lake i s p u z z l i n g .  tube  I t may occur i n Corbett  Lake, but escaped detection because the time i n t e r v a l between sampling periods was not short enough.  F a i l u r e of other  workers to show a "dawn r i s e " i n Chaoborus larvae may be due to the same reason.  In a d d i t i o n the p o s s i b i l i t y of i t occurring  for a very short time adds to the d i f f i c u l t y of d e p i c t i n g i t i n the f i e l d . The proportion of the older l a r v a l groups undergoing ascent and the time taken f o r i t to complete the descent decreased as the season progressed  ( F i g . 8 ) . The seasonal  decline i n the percentage of older larvae ascending i s probably due to progressive increase i n the rate of l i g h t i n t e n s i t y change a t dusk as i s i n d i c a t e d by the isolumes p l o t t e d i n Figure 8.  Perhaps the migrating population requires a slow  rate of l i g h t change during the t r a n s i t o r y dusk period f o r complete ascent.  The migrating larvae completing  descent more  r a p i d l y with the progression of summer can be a t t r i b u t e d perhaps to increasing darkness during the l a t e evening and e a r l y morning hours (2200-0500 hours).  Experimental r e s u l t s  i n d i c a t e that the rate of descent of the larvae may be a function of rate at which absolute darkness i s approached. The f a c t that complete migration cycles ( i n c l u d i n g "dawn r i s e " ) can be induced i n the laboratory by a r t i f i c i a l l y changing the n a t u r a l daytime l i g h t conditions ( F i g s . 14 and 15) i n d i c a t e s that l i g h t controls the timing of d i e l v e r t i c a l migration of Chaoborus f l a v i c a n s l a r v a e .  Furthermore the experiments have  shown that the animals respond only to changes of p a r t i c u l a r l y low l i g h t i n t e n s i t i e s (below 1000 l u x ) . H a r r i s and Wolfe (1955) have demonstrated complete laboratory migration cycles of Daphnia magna by c y c l i c a l l y changing the overhead l i g h t i n t e n s i t y using India i n k suspension.  However, H a r r i s (1963)  found the migration cycle of Daphnia magna to p e r s i s t under constant darkness or i l l u m i n a t i o n and therefore concluded the cycle to be a endogenous rhythm.  In the present study on  Chaoborus larvae, no such experiments have been c a r r i e d out. However the larvae w i l l remain at one depth i n the experimental tube f o r several hours voider a constant v i r t u a l l y dark cond i t i o n ; t h i s f u r t h e r suggests that the larvae have an exogenous rhythm. The d i e l v e r t i c a l migration of the l a r v a l population i n r e l a t i o n to the lake basin consisted of very l i t t l e shoreward movement during ascent but some shoreward movement during descent.  According to Siebeck (1964), an organism i n the water  i n v a r i a b l y receives maximum l i g h t i n t e n s i t y almost v e r t i c a l l y from above.  Prom t h i s i t then follows that the nearly v e r t i c a l  ascent of the larvae i s probably a f u n c t i o n of the subsurface l i g h t penetration.  " U f e r f l u c h t " (avoidance of shore) does not  appear to be a pertinent f a c t o r as larvae are found i n the l i t t o r a l zone during daytime (Humphreys, 1964) and do more inshore during.descent  ( i n d i c a t e d by echo t r a c e s ) . The shore-  ward movement during descent may be a r e f l e c t i o n of the f a c t that the animals have v i r t u a l l y no v e r t i c a l l i g h t component to orientate to and therefore are moving down i n a random  52 fashion which brings them i n t o the shore region.  Theoretical I n t e r p r e t a t i o n of the D i e l V e r t i c a l Migration When one attempts a t h e o r e t i c a l treatment of v e r t i c a l migration of Chaoborus l a r v a e , the e f f e c t of l i g h t on both the active swimming movement and buoyancy must be  considered.  Many workers have demonstrated that the a i r sacs are buoyancy organs (Krogh, 1911; Bardenfleth and Ege, 1916; Akehurst  (1922),  Damant, 1924; Holst-Christensen, 1928). On the basis of his study, Berg (1937) speculates that the v e r t i c a l migration i s a s t r i c t phototactic response which he does not describe i n any d e t a i l . On the basis of r e s u l t s from the present study, a simple sign change ( p o s i t i v e and negative) of phototaxis i s not s u f f i c i e n t to explain the v e r t i c a l migration.  In f a c t i t may  complicate matters by formulating u n r e a l i s t i c l a r v a l Therefore  behavior.  the migration may involve an i n t e r a c t i o n of the  normal larvae "seeking" an optimum l i g h t zone (low l i g h t i n t e n s i t y range), while having a constant p o s i t i v e response to g r a v i t y ^  The animals remain i n the optimum zone through  passive (buoyancy adjustment) and/or a c t i v e ( s l i g h t body movements) means.  Passive and active movements have been  observed i n the laboratory.  When the optimum l i g h t zone  disappears at dusk, the animals may move down a c t i v e l y or sink as the buoyancy r e g u l a t i o n c o n t r o l l e d by l i g h t gradually deteriorates.  At dawn the larvae may ascend a c t i v e l y or p a s s i v e l y  to the descending optimum zone i f there i s a stimulating l i g h t  53 gradient created between the animals and the optimum l i g h t zone to invoke responses.  I f there i s no such l i g h t gradient,  the optimum zone would reach the depth l e v e l of the slowly descending larvae, to invoke the previous i n t e r a c t i o n .  The  seasonal v a r i a t i o n i n the migration can be explained also by t h i s hypothesis.  Only extremely unfavourable p h y s i c a l and  chemical conditions would o f f s e t the i n t e r a c t i o n s .  B i o l o g i c a l S i g n i f i c a n c e of the D i e l "Vertical Migration The b i o l o g i c a l s i g n i f i c a n c e can be considered best from the standpoint of the migrating larvae spending at l e a s t h a l f of a 24 hour period i n the colder deoxygenated hypolimnion before migrating into the warmer oxygenated epilimnion. Juday (1921), observing that the larvae spend a good p o r t i o n of the day i n the deoxygenated hypolimnion, has suggested that the s i g n i f i c a n c e may  involve reduced predation.  He argues  that most.freshwater f i s h can not t o l e r a t e deoxygenated water more than a few hours.  Predation would c e r t a i n l y be reduced,  e s p e c i a l l y during the summer. Analysis of t r o u t stomach i n d i c a t e s that the f i s h prey heavily on the larvae during e a r l y spring and l a t e autumn i n Corbett Lake.  I t i s conceivable  also that the f i s h change d i e t s f o r reasons other than not being able to prey on the larvae. As the larvae encounter d a i l y two sets of environment, (aerobic and anaerobic) the adaptive value of d i e l v a t i c a l migration may  involve enhancement of optimum population growth.  McLaren (1963) has demonstrated e m p i r i c a l l y that v e r t i c a l  54 migration becomes i n c r e a s i n g l y important f o r surface feeding zooplankters as the surface and bottom temperatures become increasingly different.  The migration under such conditions  enables the animals to conserve and d i v e r t more energy i n t o growth and fecundity.  Migrating larvae feed predominately i n  the upper layers of the lake as v i r t u a l l y no food organism (cladocerans and copepods) can withstand anaerobic for any length of time.  conditions  Temperature d i f f e r e n c e i s very great  between the surface and bottom i n many lakes during the summers Therefore  l a r v a l growth and adult fecundity w i l l be enhanced  g r e a t l y during the summer' i f the larvae migrate.  The larvae  by spending part of the day i n deoxygenated water which may have also an energy conserving e f f e c t w i l l f u r t h e r enhance growth and fecundity (McLaren, 1963).  Therefore  larvae w i l l  be l a r g e r than i t would be i f they had not undergone v e r t i c a l migration.  Larger larvae became l a r g e r pupae which sub-  sequently metamorphose i n t o bigger adults with greater fecundity.  U l t i m a t e l y the success of any chaoborid popula-  t i o n may depend on these energy conserving  effects.  55 LITERATURE CITED Akehurst, S. C. 1922. Larva of Chaoborus c r y s t a l l i n u s (De Grur) (Corethra plumicornis F«). J . Roy. Microscop. S o c , 42: 341-372. Bainbridge, R. 1961. Migrations. Chapter 12 of volume 2 i n "The Physiology of Crustacea", Academic Press, New Xork, 681 pp. Bardenfleth, K. S., and R. Ege. 1916. On the anatomy and physiology of the a i r - s a c s of the l a r v a of Corethra plumicornis. Videnskabelige Meddelelser f r a Dansk N a t u r h i s t o r i s k Forehing, 67: 25-42. Berg, K.  1937. Contributions to the biology of Corethra Meigen (Chaoborus L i c h t e n s t e i n ) . K g l . Danske V i d . . Selsk., B i o l . Meddel, 13(11): 1-101.  Clarke, G-. L., and D. F. Bumpus. 1950. The plankton-sampler an instrument f o r q u a n t i t a t i v e plankton i n v e s t i g a t i o n . Amer. Soc. Limnol. Oceanogr., Spec. Publ. No. 5: 1-8 (2nd ed.). Cassie, R. M. 1954. Some uses of p r o b a b i l i t y paper i n the a n a l y s i s of size frequency d i s t r i b u t i o n s . Aust. J . S c i . , 5(3): 513-522. Cook, E. F. 1956. The n e a r c t i c Chaoborinae (Diptera: C u l i c i d a e ) . Univ. Minn. Agr. Expt. Sta., Tech. B u l l . , 218: . 1-102. Cushing, D. H. 1951. The v e r t i c a l migration of planktonic Crustacea. B i o l . Revs., 26: 158-192. Damant, G. C. C. 1925. The adjustment of buoyancy of the l a r v a of Corethra plumicornis. J . P h y s i o l . , 54: 345-356. Davis, C. C. 1955. The marine and fresh-water plankton. Michigan State U n i v e r s i t y Press, 562 pp. Dendy, J . S. 1956. Bottom fauna i n ponds w i t h large mouth bass only and with a combination of largemouth bass plus b l u e g i l l . J . Tenn. Acad. S c i . , 31(3): 198-207. Deonier, C. C. 1943. Biology of the immature stages of the Clear Lake gnat. Entomol. Soc. Amer. Ann., 36: 383-388.  56 Eggleton, F. E. 1932. Limnetic d i s t r i b u t i o n and migration of Corethra larvae i n two Michigan l a k e s . Mich. Acad. S c i . , A r t s and L e t t . Pap., 15: 361-388. Elgmork, K. 1959. Seasonal occurrence of Cyclops strenus. P o l i a Limnol. Scand., 11: 1-196. Eraser, F. C. 1936. On the development and d i s t r i b u t i o n of the young stages of k r i l l (Euphasis superba). Discovery Rep., 14: 3-192. Gardiner, A. C. 1933. V e r t i c a l d i s t r i b u t i o n i n Calanus finmarehicus. J . Mar. B i o l . Ass. U. K., 18: 5756T0. ' Hamilton, A. L. MS, 1958. The macroscopic bottom fauna of Kenosee Lake. M.A. Thesis, U n i v e r s i t y of Saskatchewan. Hardy, A. C. 1956. The Open.Sea. C o l l i n s , London. 335 pp.  1. The world of plankton.  H a r r i s , J . E. 1963. The r o l e of endogenous rhythms i n v e r t i c a l migration. J . Mar. B i o l . Ass. U.K., 43: 153-166. H a r r i s , J . E., and U. K. Wolfe. 1955. A laboratory study of v e r t i c a l migration. Proc. Roy. Soc. B, 145: 280290. Holst-Christensen, P. 1928. Bidrag t i l Kendskabet om Corethralarvens hydrostatiske Mekanisme. Vedenskabelige Meddelelser f r a Dansk. N a t u r h i s t o r i s k Porening, 67: 25-42. Humphreys, R. D. MS, 1964. S p a t i a l and temporal d i s t r i b u t i o n of invertebrate organisms i n h a b i t i n g the Chara zone. M.Sc. Thesis, U n i v e r s i t y of B r i t i s h Columbia. Hunt, B. P. 1958. Limnetic d i s t r i b u t i o n of Chaoborus larvae i n a deep F l o r i d a lake (Deptera). F l o r i d a Entomol., 41(2): 111-116. Juday, C.  1921. Observations on the larvae of Corethra punctipennis Say. B i o l . B u l l . , 40(5): 271-286.  Krogh, A.  1911. On the h y d r o s t a t i c mechanism of the Corethra l a r v a w i t h an account of methods of microscopical gas a n a l y s i s . Skand. Arch, f u r P h y s i o l . , 25: 183203.  57 Kutkuhn, J . H. 1958. Notes on the p r e c i s i o n of numerical and volumetric plankton estimates from small-sample concentrates. Limnol. Oceanogr., 3(1): 69-83. Langford, R. R. 1938. Diurnal and seasonal changes i n the d i s t r i b u t i o n of the l i m n e t i c Crustacea of Lake N i p i s s i n g . Univ. Toronto Stud., B i o l . Ser., 45: 1-142. L i n d q u i s t , A. W., and C. C. Deonier. 1943. Seasonal abundance and d i s t r i b u t i o n of the larvae of the Clear Lake gnat. J . Kans. Entomol. S o c , 16: 193-202. Lund, J . W. G., C. K i p l i n g and E. D. La Cren. 1958. The inverted microscope method of estimating a l g a l numbers and the s t a t i s t i c a l basis of estimations by counting. Hydrobiologia, 11(2): 143-170. MacDonald, W. W. 1956. Observations on the biology of chaoborids and chironomids i n Lake V i c t o r i a and on the feeding habits of the "elephant-snout f i s h " (Mormyrus kannumi Torsk.). J . Anim. E c o l . , 25: 36-53. McLaren, I . A. 1963. E f f e c t s of temperature on growth of zooplankton, and the adaptive value of v e r t i c a l migration. J . F i s h . Res. Bd. Canada, 20(3): 685727. M i a l l , L. C. 1895. The n a t u r a l h i s t o r y of the aquatic i n s e c t s . MacMillan and Co., London, 395 pp. M i l l e r , R. B. 1941. Some observations on Chaoborus p u n c t i pennis Say. (Diptera, C u l i c i d a e ) . Can. Entomol., 73: 79-039. Muttkowski, R. A. 1918. The fauna of Lake Mendota. Trans. Wis. Acad. S c i . , A r t s and L e t t . , 1 9 ( l ) : 374-482. Northcotey T. G. 1964. Use of high-frequency echo sounder to record d i s t r i b u t i o n and migration of Chaoborus larvae. Limnol. Oceanogr., 9(1): 87-91. Rawson, D. S. 1930. The bottom fauna of Lake Simcoe and i t s r o l e i n the ecology of the l a k e . Publ. Ont. F i s h . Res. Lab., 40(34): 1-183. Raymont, J . E. G. oceans.  1963. Plankton and p r o d u c t i v i t y i n the Pergamon Press, London, 660 pp.  58 R i c k e r , W. E. 1938. On adequate q u a n t i t a t i v e sampling of the p e l a g i c net plankton of a lake. J . F i s h . Res. Bd. Canada, 4 ( l ) : 19-32. Siebeck, 0. 1964. Researches on the behavior of planktonic crustaceans i n the l i t t o r a l zone. Verh. i n t . Ver. Limnol., 15(2): 746-751. Wood, K. G. 1956. Ecology of Chaoborus (Diptera: C u l i c i d a e ) i n an Ontario l a k e * Ecology, 37(4): 639-643. Woodmanse, R. A., and B. J . Grantham. 1961. D i e l v e r t i c a l migrations of two zooplankters (Mesocyclops and Chaoborus) i n a M i s s i s s i p p i l a k e . Ecology, 42(4): 619-628. Worthington, E. B., and C. K. Ricardo. 1936. S c i e n t i f i c r e s u l t s of the Cambridge expedition to the East A f r i c a n Lakes, 1930-31 - No. 17. The v e r t i c a l d i s t r i b u t i o n and movements of the plankton i n Lakes Rudolf, Naivasha, Edward and Bunyoni. J . Limn. Soc. Zool., 40: 33-39. Tentsch, C. S., and A. C. Duxbury. 1956. Some of the f a c t o r s a f f e c t i n g the c a l i b r a t i o n number of the ClarkeBumpus q u a n t i t a t i v e plankton sampler. Limnol. Oceanogr., l ( 4 ) : 268-273.  APPENDIX I . Determination of the c a l i b r a t i o n value of the Clarke-Bumpus sampler towed a t several depths f o r a 61 m distance a t boat speed of 2.5 knots. Without Net Towing Depth ( i n metres)  Corrected Depth ( i n metres)  Surface  —  Average No. of Revolutions (3 Tows)  With No. 10 Net  C a l i b r a t i o n Value i n L i t e r s per Revolution  Average No. of Revolutions (3 Tows)  C a l i b r a t i o n Value i n L i t e r s per Revolution  135.3  5.7  126.0  6.2  1.97  133.3  5.8  125.3  6.3  4  3.80  136.0  5.6  120.0  6.6  6  5.56  137.3  5.7  124.7  6.3  8  7.42  135.3  5.7  124.7  6.3  10  9.21  136.7  5.6  126.3  6.2  12  10.87  135.7  5.7  129.6  6.1  2  .  Ul vO  60 APPENDIX I I .  Volume of water passed through and the number of Chaoborus larvae caught by the Clarke-Bumpus sampler (with no. 10 net attached) towed a t several depths f o r a 61 m distance a t a boat speed of 2.5 knots.  Corrected Depth ( i n m)  Sample No.  Time  No. of Larvae  No. of Larvae per 100 L  Surface  1 2 3  1252 1256 1301  466 649 956  93.20 119.08 189.68  1.97  1 2 3  1305 1314 1320  1374 1675 1278  267.83 340.44 237.98  3.80  1 2 3  1325 1330 1333  4235 4187 4350  922.66 809.86 870.00  5.56  1 2 3  1338 1345 1350  1833 2128 2067  360.83 408.45 410.2  7.42  1 2 3  1357 1402 1409  710 543 809  142.12 103.43 159.25  9.21  1 2 3  1415 1429 1434  326 317 401  63.55 60.38 77.56  10.87  1 2 3  1439 1444 1448  189 190 214  35.73 35.65 40.15  61  APPENDIX I I I .  Comparison of the volume of water i n the compartments of the subsampler using d i f f e r e n t t o t a l volumes.  Volume of Water Used ( i n ml.)  Compartment  Volume of Water i n Each Compartment ( i n ml.)  about 1000  A B C D E F  164 164 163.8 164 166 165  about  750  A B C D E F  122.2 121 122 122 122 122.3  about  500  A B C D E F  81 80 80.3 81 81 80.8  about  250  A B C D E F  40.5 41 41 40 41 41  APPENDIX IV. Test of the r e l i a b i l i t y of the subsampler, using d i f f e r e n t volume of water and d i f f e r e n t number of larvae. A 0.05 s i g n i f i c a n c e l e v e l was used. No. of Approximate Volume of Water Used ( i n ml.) Larvae Used  Compartment  No. of Larvae i n Each Compartment  250  222  A B C D E F  29 40 41 41 44 27  500  203  A B C D E F  33 40 36 33 27 34  750  239  A B C D E F  35 48 42 35 37 41  250  599  A B C D E F  X Value  Type of Distribution  7.14  Random  2.69  Random  3.21  Random  1.50  Random  N.B. (1 l a r v a l e f t i n the subsampler )  104 94 105 93 104 N.B. (2 larvae 97 l e f t i n the subsampler )  0> to  APPENDIX IV Continued No. of Approximate Volume of Water Used ( i n ml.) Larvae Used 500  750  Compartment  667  573  . 250  1022 •  A B C D E F  122 94 91 108 : 93 125  A. B C D E P  104 98 103 83 88 96  A *B  **c  D  F 250  *154  Prom B Compartment  No. of Larvae i n Each Compartment  A B C D E • F  Type of Distribution  9.09  Random  3.64  Random  6.96  Random  2.57  Random  2  . _  N.B. (4 larvae l e f t i n the subsampler )  161 154 184 N.B. (2 larvae 159 l e f t i n the 169 subsampler ) 193  20 29 25 24 25 30  X Value  N.B. (2 larvae l e f t i n the subsampler )  APPENDIX IV Continued Approximate Volume No. of of Water Used ( i n ml.) Larvae Used  Compartment  No. of Larvae i n Each Compartment  500  **184 Prom C Compartment  A B C D E P  29 29 29 29 33 35  750  ***169 Prom E Compartment  A B C D E F  32 26 25 24 N.B. (2 larvae 32 l e f t i n the ) 27 subsampler  500  750  1143  1039  A B C D E P  191 181 181 201 202 185  A B C D E P  186 165 170 176 174 166  X Value  Type of Distribution  1.15  Random  2.21  Random  1.98  Random  1.78  Random  N.B. (2 larvae l e f t i n the subsampler )  65  APPENDIX V.  Time Period 1120-1207 hours  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during 24 hour f i e l d s e r i e s of June 17-18, 1963  Depth i n . Metres  Class 0  .99 1.93 2.91 3.76 4.73 5.64 6.66 7.52 8.56 8.83 9.89  10.8 55.5 45.7 154.9 42.0 153.2 64.8 191.2 91.8 25.6 13.5 62.5 6.3 37.3 0.3 9.3 0.1 7.1  10.60 11.26 11.87 hours  Surface 0.97 1.90 2.85 3.76 4.67 5.48  0.1 7.0 0.8 43.9 0.7 41.0 0.8 4.2 77.6 213.3 80.3 213.0 52.6 170.1 21.0 108.0  Class 1 64.3 143.7 146.5 231.2 229.4 427.1 295.5 598.7 131.0 292.9 135.7 303.3 109.6 210.9 46.0 104.6 6.1 23.0 ' 3.6 18.3 2.0 14.5 0.8 11.0 0.8 11.5 17.3 102.8 56.3 172.0 46.5 157.5 164.7 345.1 547.5 840.0 166.3 343.9 57.8 176.3  Class 2 .  79.4 166.4 71.7 155.7 101.8 244.9 48.2 163.3 53.2 171.9 31.9 136.5 30.5 93.0 41.5 97.8 21.0 47.7 7.9 26.7 17.1 41.2 10.5 31.0 9.0 29.2 2.0 14.6 72.2 203.9 61.5 181.5 63.0 186.0 120.7 279.2 103.5 249.0 12.2 89.2 7.5 76.5  Class 3  Class 4  0.3 27.2 2.3 33.9 11.8 86.3 7.8 79.3 4.8 70.2 30.3 80.8 21.0 47.7 21.6 48.3 36.4 68.9 44.1 79.5 17.0 41.8 46.3 82.4 4.7 69.0 45.3 153.7 74.3 204.0 26.7 123.9 7.5 76.5  5.2 22.2  0.1 7.3 1.3 12.8 0.7 41.0 4.5 66.0 0.8 43.9  66 APPENDIX V Continued Time Period  Depth i n Metres 6.24 7.52  hours  Surface 0.97 1.88 2.80 3.68 4.53 5.53 6.34 7.31 8.15 8.99 9.71 10.28  Class 0  Class 1  Class 2  Class 3  Class 4  10.6 31.3 5.0 15.4 0.8 29.3  34.9 67.2 6.4 17.8 34.1 100.8 39.2 110.9 34.8 102.6 205.8 408.2 153.9 334.3 138.1 308.8 72.1 203.9 34.4 86.8 4.9 71.5 6.9 27.2 3.7 37.3 0.3 9.8 0.3 10.0  0.3 9.1 3.1 12.0 31.3 95.5 42.2 116.0 53.8 132.4 32.8 140.2 76.1 215.2 32.5 139.0 4.7 69.0 7.9 40.6 62.6 191.0 14.6 40.2 5.9 42.8 31.8 64.3 .2.2 16.3  0.8 29.3 6.8 49.9 6.6 48.4 0.8 45.9 0.8 46.3 4.9 71.5 7.8 80.0 15.2 55.5 80.5 221.0 43.5 82.2 47.6 117.1 38.7 73.8 19.2 46.2  0.1 7.8  4.1 42.2 32.8 140.2 51.3 173.8 43.9 160.1 26.7 123.9 11.3 48.2 1.6 58.5  67  APPENDIX Y I .  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during the 24 hour f i e l d s e r i e s of J u l y 20-21, 1963.  Time Period  Depth. i n Metres  1128-1223 hours  2.88 3.78 4.67 5.52 6.29  Class 0 0.6 6.2 0.3 , 16.4 0.4 22.4 0.6 21.1  Class I 2.4 10.4 1.8 25.8 6.4 46.7 6.4 38.3  7.13 7.95 8.66 9.53  1.6 23.4 4.8 70.2  10.06 10.90 11.47 12.14 12.61 2123-2211 hours  Surface 0.99 1.92 2.87  0.8 44.7  3.76 4.64 5.48  0.3 18.9  1.6 57.5 0.8 44.7 0.7 41.0 13.5 57.7 4.0 40.7  Class 2 23.8 36.6 125.9 216.6 103.8 203.5 96.0 176.2 67.6 . 130.0 80.6 170.8 92.1 193.2 82.7 154.1 58.0 120.0 97.4 245.9 27.2 92.0 7.9 28.8 5.7 22.4 0.7 6.8 31.9 136.5 49.5 167.6 8.0 81.4 16.1 95.9 82.0 242.0 96.6 184.1 87.0 180.0  Class 3  Class 4  1.3 16.0  ( 3.9 28.5 6.4 46.7 2.6 38.6 16.5 55.9 38.8 91.5 91.8 236.3 92.2 193.2 61.5 102.4 44.0 79.0 16.2 32.3 167.6 351.2 73.4 207.5 37.5 146.8 78.3 207.8 39.0 166.8 7.4 44.2 11.2 57.5  0.1 8.2 0.07 3.7 0.8 44.7 0.8 44.7  68  APPENDIX VI Continued Time Period  Depth i n Metres 6.29 7.06 7.95 8.66  Class 0  Class 1  Class 2  0.3 14.9 0.7 26.3 0.1 7.5  0.3 14.9 3.7 37.3 45.9 83.1 0.3 9.6  43.1 97.9 73.9 156.6 0.3 9.6 47.0 84.6 97.4 245.9 51.2 87.8 9.9 22.4 29.3 52.7 18.4 44.2 16.3 31.8 73.7 141.8 117.3 221.9 87.0 180.0 79.8 165.0 107.6 203.4 93.8 189.6 68.0 147.8 74.6 166.8 85.4 226.7 8.3 38.5 16.0 68.2 2.6 15.5  9.43 9.95 0511-0600 hours  Surface .99 1.92 2.87 3.78 4.64 5.48 6.49 7.19 8.02  0.1 4.4 0.2 5.9 0.3 9.6 0.06 3.4 0.3 9.6 0.8 28.7 2.4 35.1 0.4 20.5  0.06 3.4 0.08 4.6 1.3 13.6 0.1 4.4 5.9 34.9 2.4 35.1 2.4 35.1 0.1 4.4  8.75 9.33 10.07 10.78 11.33 11.99  0.4 24.6  Class 3. Class 4 1.6 23.4 0.4 20.5 2.9 17.4 2.0 14.3 0.9 7.1 0.08 4.6 0.3 9.6 1.7 8.8 0.3 9.6 0.4 22.4 2.4 35.1 5.9 42.8 11.2 57.5 28.2 . 86.0 53.6 135.2 67.1 198.0 57.3 115.9 93.8 189.6 16.3 39.2  0.2 13.7 0.4 22.4 3.3 17.0  69 APPENDIX V I I .  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during the 24 hour f i e l d s e r i e s of August 18-19, 1963.  Time Period  Depth . .n Metres  1115-1204 hours  6.86  Class 0  Class 1  7.63 8.39 9.12 9.83  64.7 146.9 0.4 22.4  10.24 10.40 11.49 12.78 2108-2200 hours  Surface 0.95 1.91 2.76  0.2 12.0 1.8 63.2  1.7 62.0 0.4 15.5  3.66 4.50 5.44 6.40 7.13  1.7 62.0 0.1 7.0  1.5 54.5 0.3 9.0  7.95 8.66 9.23 9.95  0.07 4.1  Class 2  Class 3  24.3 44.4 30.5 62.1 191.4 396.0 213.9 416.7 67.8 151.7 58.3 137.3 20.6 80.9 2.2 32.2 14.4 52.4 46.5 169.7 23.0 61.1 19.3 11.5 7.3 74.6 77.7 219.7 35.5 139.2 13.8 100.8 18.3 43.0 25.6 41.5 15.3 39.4 6.8 26.7 3.0 17.6 0.73 7.5  1.3 13.7 14.0 102.7 27.1 126.1 61.5 142.1 61.5 142.1 129.1 244.1 68.0 147.8 127.7 215.5 13.8 100.8 52.3 104.7 35.1 150.1 56.3 172.0 28.7 133.5 21.2 108.9 40.5 158.5 19.3 44.5 2.7 16.0 12.2 34.6 11.2 34.1 7.2 26.4 6.7 19.0  Class '  0.4 22.4  2.2 32.2 13.8 100.8 2.2 21.9 14.6 52.7  0.1 7.0 2.7 16.0 2.1 15.6 1.4 14.8 3.0 17.6 6.1 18.1  70 APPENDIX V I I Continued Time Period  Depth i n Metres  Class 0  Class 1  10.78 11.61 0515-0600 hours  0.95 1.87 4.46 5.44 6.13 6.86 7.46 7.99 8.67 9.46 9.96 10.40 11.15 11.12  0.1 4.4 0.1 7.5 0.07 3.7  0.09 3.3 0.09 3.5 0.06 3.4 0.8 11.7 0.1 4.8 0.3 9.5 0.4 22.4 0.8 28.7  Class 2  Class 3  Class 4  2.0 10.5 0.3 3.9 11.5 22.4 13.1 25.1 12.8 26.8 26.9 56.9 27.9 47.9 55.4 95.0 74.5 157.9 67.8 151.7 55.1 132.5 2.4 35.1 10.7 63.9  14.8 31.3 5.1 13.1 2.0 7.9 1.0 6.0 0.6 6.2 0.3 9.6 0.7 6.8 13.1 35.9 14.8 63.1 27.5 89.0 134.1 244.7 61.5 142.1 71.2 167.8 120.0 254.9 105.9 221.8 42.4 109.2  2.5 11.6 1.2 6.4  0.8 28.7 13.6 63.1 1.0 35.1 3.6 52.2 0.5 28.2 14.8 63.1  71 APPENDIX V I I I .  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l larvae i n the l a r v a l classes f o r samples taken during the 24hour f i e l d s e r i e s of September 21-22, 1963.  Time Period  Depth L Metres  0758-0838 hours  8.19  Class 0  Class 1  9.12 9.83 10.65 11.18 12.14 12.61  1125-1205 hours  7.37 8.19 9.12 9.83 10.65 11.18 12.14 12.61 14.72  1530-1617 hours  7.37 8.19 9.12 9.83 10.65 11.18  0.05 2.7 0.1 7.5 0.4 24.6 0.4 24.6 .  Class 2 118.5 237.6 47.0 124.7 41.3 161.6 6.4 46.7 7.0 51.4 4.4 44.8 3.4 13.5 16.4 29.9 18.4 44.2 27.2 92.2 38.6 119.4 36.9 108.9 23.7 86.5 4.1 21.1 6.5 27.8 8.4 21.7 10.6 . 26.0 60.6 145.8 20.2 68.3 12.3 63.2 7.5 54.7 0.9 51.2  Class 3 75.1 173.7 81.7 177.4 86.9 238.8 61.5 142.1 85.2 182.6 50.5 130.0 17.2 34.8 10.7 21.5 12.3 34.6 57.1 140.5 47.0 124.7 99.7 203.3 99.7 203.3 54.1 96.4 38.2 77.2 19.0 37.3 9.3 24.1 14.9 69.4 63.1 135.3 106.7 213.8 133.7 254.8 155.3 347.2  Class  0.9 49.2 11.2 57.5 17.6 75.1 12.3 63.2 5.4 17.2  2.6 38.6 0.4 24.6 0.4 24.6 0.4 24.6 0.3 10.5 0.4 24.6  9.7 57.5 13.1 67.3 9.1 93.2  72 APPENDIX V I I I Continued Time Period  Depth i n Metres  Class 0  Class 1  12.14 12.61 1930-2007 hours  Surface 0.97 1.90 2.78 3.63 4.53 6.12 6.71 7.37 8.19 9.12 9.83 10.65 11.18 12.14 12.61  2132-2216 hours  Surface 0.97 1.91 2.78 3.66  0.1 8.2  Class 2 0.9 31.6 1.8 25.8 1.8 18.7 3.2 19.2 .2.1 15.6 6.3 24.5 11.3 34.4 6.9 26.9 7.6 29.9 2.5 11.6 2.8 12.8 10.1 32.6 2.3 17.1 1.4 14.9 0.9 12.9 6.9 26.9 0.1 4.8 0.2 5.6 0.4 13.2 0.310.5 4.5 21.0 7.2 26.2 5.9 25.0  Class 3  Class 4  53.6 135.2 29.0 79.6 66.0 118.5 36.7 72.9 32.3 64.8 19.4 45 i-8 22.5 52.1 21.4 50.3 15.0 42.3 14.2 30.4 13.2 29.9 21.4 50.3 28.4 60.9 17.9 45.1 26.0 57.4 21.4 50.3 9.2 22.1 13.2 29.6 44.5 89.1 24.9 55.6 35.7 69.4 20.5 47.4 30.7 64.4  9.7 57.5 18.1 61.3 7.3 31.3 10.1 32.6 4.5 21.0 2.1 15.6 2.3 17.1 0.3 10.5 1.6 9.6 0.2 5.9 0.1 8.2 0.3 10.5 0.9 12.9 0.3 10.5 0.9 12.9 6.6 18.1 5.4 17.4 5.1 26.3 13.5 38.0 7.2 26.2 1.3 13.6 3.2 19.2  73 APPENDIX V I I I Continued Time Period  Depth i n Metres 4.50 5.30 6.06 6.63 7.09 8.48 9.33 9.95 10.65 11.19 11.99 12.78  2322-0002 hours  Surface 0.98 1.90 2.80 3.60 4.42 5.30. 6.06 6.63 7.28  Class 0 0.1 8.2  Class 1  Class 2  Class 3  Class 4  4.1 21.1 5.0 23.1 7.5 21.1 4.0 14.4 4.4 16.0 13.5 38.0 3.2 19.2 3.2 19.2 1.5 14.9 5.6 17.2 0.1 5.3 1.2 9.1 5.9 25.0 4.1 14.0 5.0 16.3 5.0 16.3 2.9 12.5 4.8 22.3 3.9 19.9 13.5 38.0 5.0 23.1 18.4 59.3  14.5 39.8 21.4 50.3 20.4 40.5 19.0 37.3 11.9 28.0 15.7 41.6 27.2 59.1 21.4 50.3 28.4 60.9 20.3 39.0 16.6 33.9 11.4 26.8 16.8 43.3 11.3 25.3 11.9 26.9 16.0 33.0 7.2 19.9 16.2 41.7 20.1 47.4 27.2 59.12 15.7 41.6 34.6 .85.1  0.3 10.5 3.2 19.2 0.3 7.2 4.5 15.4 0.08 4.6 0.9 12.9 5.0 23.1 2.9 12.5 5.0 16.3 2.2 11.2 5.0 23.1 0.7 6.8 1.6 9.6 0.7 7.5 0.4 6.4 0.8 12.4 0.39.9 4.1 21.1 2.3 17.1 5.3 19.2  74 APPENDIX V I I I Continued Time Period  Depth i n Metres  Class 0  7.99 9.12 9.59 10.65 11.19 11.82 12.61 0332-0415 hours  Surface .97 1.90 2.78 3.66 4.50 5.35 6.18  :  6.93 7.61 8.19 8.79 9.95 10.78 11.19 12.29  .  Class 1  Class 2  Class 3  Class 4  39.5 108.6 1.5 55.5 1.3 12.9 0.1 7.5 0.5 5.0 0.1 3.2 0.8 5.7 1.3 7.0 2.0 8.3 1.4 7.0 2.1 8.2 1.1 7.8 2.9 12.5 2.3 10.3 5.9 25.0 3.3 13.0 14.2 30.4 8.3 84.4 0.9 33.6 1.4 14.1 0.1 8.2 1.2 8.6 1.8 10.7  30.7 93.8 82.5 218.9 29.6 61.0 21.6 49.0 10.6 22.0 7.5 16.9 7.1 16.8 7.9 18.0 6.7 16.2 7.9 18.0 9.0 19.0 12.9 27.7 10.1 24.3 7.1 18.9 19.0 46.8 15.4 31.8 11.3 26.0 140.7 31.4 83.2 183.3 39.4 75.2 28.4 60.9 24.6 44.9 13.8 30.9  8.8 52.3 21.6 111.0 6.9 25.3 1.3 13.6 0.8 5.7 2.1 8.2 1.1 6.4 .05 2.7 1.4 7.0 1.7 7.7 0.3 3.9 0.4 5.9 1.6 9.6 2.3 10.5 0.3 10.5 2.0 10.1 1.46 14.9 1.7 59.6 13.1 67.3 10.6 32.4 14.5 39.8 3.4 13.5 4.4 16.0  75 APPENDIX V I I I Continued Time Period  Depth i n Metres  Class 0  Class 1  12.61 0513-0555 hours  3.71 4.53 4.40 6.18 7.06 7.79 8.29 9.01 9.83 10.78 11.75 11.96 12.61  0.1 7.5  Class 2  Class 3  Class 4  .05 2.7 5.4 13.7 5.4 13.9 4.9 14.8 13.2 36.2 13.2 36.2 5.3 22.7 8.8 89.6 49.5 167.6 9.7 57.5 2.4 35.1 0.1 8.2 0.3 10.5 1.9 9.6  8.7 19.1 18.2 31.0 8.0 17.8 9.2 21.7 24.7 53.7 11.2 33.0 26.9 56.9 128.2 302.0 116.5 274.6 50.5 130.0 55.1 132.5 39.2 76.4 23.7 53.9 11.3 25.3  5.2 13.7 .09 3.2 .05 2.6 3.7 19.2 0.1 7.5 4.5 21.0 8.8 89.6 8.0 81.4 20.6 80.8 6.4 46.7 10.2 32.6 9.1 30.7 7.1 18.9  76 APPENDIX IX. Lower and upper confidence l i m i t s expressed i n members per 100 1 f o r estimated t o t a l counts of larvae i n samples taken during the 24 hour f i e l d s e r i e s of June 16-17, 1963. Time Period  Depth i n Metres  Lower Limit  Upper Limit  0805-0922 hours  0.97 1.90 2.87 3.76 4.67 5.60 6.45  101.3 598.6 298.0 263.4 298.0 217.1 98.4  130.4 910.3 453.1 495.0 525.5 288.6 149.0  1120-1207 hours  .99 1.93 2.91 3.76 4.73 5.64 6.66 7.52 8.56 8.83 9.89 10.60 11.26  170.2 281.4 494.3 528.7 313.7 339.2 185.9 160.7 60.9 43.9 65.7 63.8 35.0  286.6 429.8! 730.3 816.4 578.2 587.5 312.5 115.2 103.7 79.4 107.9 106.3 68.2  1522-1612 hours  0.97 1.96 2.87 3.80 4.54 5.64 6.34 . 7.42  132.5 557.7 443.3 406.7 285.6 191.8 139.1 87.2  196.0 862.0 713.1 682.6 512.7 259.0 202.6 140.9  1922-2005 hours  Surface 0.97 1.92 2.88 3.80 4.76 5.68 6.49 7.06  127.7 215.3 423.6 383.1 396.4 196.1 105.6 126.9 94.5  187.0 288.9 523.4 638.6 655.3 323.5 186.1 184.1 143.7  2110-2211 hours  Surface .97 1.90  158.5 227.6 264.8  335.7 423.7 477.0  77 APPENDIX IX Continued Time Period  Depth i n Metres  Lower Limit  Upper Limit  2.85 3.76 4.67 5.48 6.24 7.52  509.8 842.9 297.5 121.5 52.9 18.7  807.8 195.5 511.0 276.0 92.0 35.6  2310-1200 hours  Surface 0.97 1.91 2.85 3.86 4.76 5.53 6.62  114.5 109.9 158.8 713.0 767.3 428.5 163.8 58.3  166.9 163.9 220.3 841.6 1107.5 437.4 227.3 97.2  0105-0153 hours  Surface .97 1.92 2.85 3.76 4.64 5.48 6.29  99.2 110.8 565.2 807.0 855.3 237.0 130.1 66.2  150.0 164.1 878.3 1163.1 1216.1 280.4 188.4 110.3  0317-0404 hours  Surface .96 1.90 2.85 3.76 4.64 5.60 6.43  114.7 120.3 215.9 587.6 391.3 308.8 152.4 108.5  166.2 177.4 290.4 889.7 652.2 398.7 215.8 158.2  0512-0600 hours  Surface 0.97 1.88 2.80 3.68 4.53 5.53 6.34 7.31 8.99 9.71  88.6 114.3 132.4 340.3 355.9 286.9 158.5 97.2 204.0 71.0 84.0  183.3 222.7 244.1 582.2 612.4 516.8 335.7 176.1 404.7 152.2 131.4  •  APPENDIX X.  Time Period  Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l counts of larvae i n samples taken during the 24 hour f i e l d series of J u l y 20-21, 1963. Depth . i n Metres  Lower Limit  Upper Limit  0815-0909 hours  7.13 7.95 8.66 9.53 10.06 10.90  142.5 132.8 323.1 240.8 209.8 74.4  203.1 188.9 411.0 317.7 282.2 115.9  1128-1223. hours  2.88 3.78 4.67 5.52 6.29 7.13 7.95 8.66 9.53 10.06 10.90 11.47 12.14  32.3 169.8 124.1 120.0 78.0 97.0 103.2 109.1 119.7 241.9 133.0 74.6 54.9  53.7 234.1 231.1 204.9 143.9 194.4 208.5 186.3 200.9 453.4 249.3 122.9 92.1  1521-1602 hours  9.33 9.95  443.4 319.4  540.8 406.7  1920-2012 hours  9.80 10.18  324.5 226.7  412.3 295.4  2123-2211 hours  Surface 0.99 1.92 2.87 3.76 4.64 5.48 6.29 7.06 7.95 8.66 9.43  248.2 161.2 67.1 118.5 150.2 145.2 1241.2 53.7 95.1 49.2 57.2 97.4  462.2 341.6 198.0 269.3 347.3 243.2 231.1 113.9 186.6 87.7 95.8 245.9  79 APPENDIX X Continued Time Period  Depth i n Metres  Lower Limit  Upper Limit  2307-2354 hours  3.82 4.70  224.8 279.8  299.1 358.8  0320-0400 hours  3.82 4.67  191.7 , 182.7  246.8 250.8  0511-0600 hours  10.07  23.1.6.  284.3  80 APPENDIX X I . Lower and upper confidence l i m i t s expressed i n numbers per 100 1 f o r estimated t o t a l counts of larvae i n samples taken during the 24 hour f i e l d s e r i e s of August 18-19, 1963. Time Period  Depth i n Metres  Lower Limit  Upper Limit  0515-0600 hours  6.13 6.86 7.46 7.99 8.67 9.46 9.96 10.40 11.12  31.3 79.1 102.2 114.1 227.5 93.8 102.4 129.5 68.6  53.2 125.3 196.6 217.5 363.2 189.6 214.6 267.9 149.0  

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