FISHERY BULLETIN: VOL. 70, NO. 2 



Late summer 1966 

 Early summer 1967 

 Late summer 1967 



Fry-zooplankton 



Yearllng-zooplankton 



Fry-zooplankton 

 Yearllng-zooplankton 



0.975*** 



.675 



.700 

 .600 



0.975* 



.425 



.225 

 -.025 



Significant at P = 0.20. 

 Significant at P = 0.10. 

 Significant at Z' = 0.05. 



0.800* 



.300 



.900* 

 .825* 



0.800* 



.700 



1.00**' 

 1.00**' 



of organisms in the yearling foreguts showed 

 a similar change; for Cyclops and Bosmina 

 r rr 0.66 (significant at P = 0.10) and 0.71 

 (significant at P = 0.05), respectively. Cor- 

 relation was not significant for fry (r = 0.01 

 and 0.22, respectively) . The percentage of cal- 

 anoid copepods in the fish foreguts remained 

 constant in spite of an increase from early to 

 late summer in the zooplankton hauls (Table 3) . 

 Although diflferences were significant in the 

 percentage composition of organisms in the zoo- 

 plankton hauls and in the fish foreguts, the fish 

 fed predominantly on those organisms which 

 were most abundant in the zooplankton hauls. 

 Rank correlation coefficients (?d) were used in 

 comparing the percentage of Cyclops, Bosmina, 

 calanoid copepods, Daphnia, and Holopedlum in 

 the zooplankton hauls and in the foreguts, and 

 showed very good correlation in several areas 

 and sampling periods and, with one exception, 

 were always positive (Table 5). 



COMPARISON OF FRY AND 

 YEARLING DIETS 



Cyclops and Bosmina were the major food 

 items in the diet of both fry and yearlings al- 

 though the percentage of the former was greater 

 and the percentage of the latter smaller in the 

 yearling foreguts than in the fry foreguts (Table 

 3) . Differences in the foregut contents may re- 

 sult from slight diflferences in habitat and hence 

 from diflferences in available food. 



To minimize this possibility only those sam- 

 ples that included at least five fry and five year- 

 lings were examined. The relationship between 

 the two age groups in the percentage of Cyclops 



and Bosmina in the foreguts appeared linear 

 (Figures 4 and 5) and a regression analysis was 

 performed. The slope (b) was significantly 

 greater than zero (P = 0.05) for both zoo- 

 plankters; thus, the two age groups have similar 

 food habits. However, the hypothesis 6 = 1 

 was rejected (P = 0.05) ; therefore, I con- 

 cluded that fry consume more Bosmina and less 

 Cyclops than yearlings. The positive intercept 

 in Figure 4 and b less than 1 in Figures 4 and 5 

 indicate that the percentage of Cyclops and Bos- 

 mina vary less in yearling than in fry foreguts. 



DISCUSSION AND CONCLUSIONS 



Cyclops and Bosmina were the most abundant, 

 and calanoid copepods, Daphnia, and Holope- 

 dlum, the least abundant zooplankters in the fish 

 foreguts and in the zooplankton hauls. How- 

 ever, the percentage composition of organisms 

 in fish foreguts diflfered significantly from those 

 in the zooplankton hauls in that: fry contained 

 more Bosmina; yearlings contained more Cy- 

 clops; fry and yearlings contained less calanoid 

 copepods than the zooplankton hauls. 



Discrepancies in estimates of available food 

 and diet are due to sampling error and selective 

 feeding. Spatial and temporal diflferences in the 

 sampling of zooplankton and fish, and diel and 

 depth variations in available food and feeding 

 activity probably accounted for some discrepan- 

 cy. Fowler and Lenarz (1965) established diel 

 and depth variations in the percentage compo- 

 sition of the standing zooplankton stock in the 

 lake. Northcote and Lorz (1966) showed diel 

 changes in the food of resident sockeye salmon 

 (kokanee) in Nicola Lake, British Columbia, 



360 



