HOAG: SUMMER FOOD OF JUVENILE SOCKEYE SALMON 



larly to the organisms in the foregut. Samples 

 were grouped by area and sampling period. The 

 sampling periods were: 



1. Late summer 1966 (August 10-26). 



2. Early summer 1967 (June 18-30). 



3. Late summer 1967 (August 22-September 



15). 



RESULTS 



The numbers of fry and yearlings and the 

 numbers of zooplankton samples by area and 

 sampling period are listed in Table 1. Catches 

 of yearlings in 1966 and of fry in the early sum- 

 mer of 1967 were small and were excluded from 

 the analysis. Both fry and yearlings occurred 

 in varying numbers in nearly all samples during 

 the late summer of 1967. The mean fork length 

 by area and sampling period ranged from 50 to 

 58 mm for fry and from 71 to 96 mm for year- 

 lings. 



Table 1. — Summary of samples of fish and zooplankton 

 by area and sampling period. 



f 10- 



o Yearling Y = - 420 33 + I 65 x 



• Fry Y-199 16+ 04 x 



3 6 9 



Number of organisms per cubic meter (tnousands) 



Figure 2. — Relationship between the number of organ- 

 isms per foregut and the number of zooplankton per 

 cubic meter. 



Sampling period 



Number of Number of Number of 

 Area Age group fish fish zooplankton 



samples examined samples 



FEEDING ACTIVITY 



Most juvenile sockeye salmon (94%) con- 

 tained some food. Temporal and spatial dif- 

 ferences in the mean number of organisms in 

 the foregut of juvenile sockeye salmon were 

 apparent although the number of organisms per 

 foregut varied considerably between samples 

 within areas and sampling periods (Table 2). 

 The number of organisms consumed per foregut 

 increased from early to late summer and from 

 area IV to area L 



The mean number of organisms per foregut 

 by age group and the mean number of organisms 

 per cubic meter in each area and sampling pe- 

 riod are plotted in Figure 2. The positive slopes, 

 significant at P = 0.05, indicate that feeding 

 was in proportion to the abundance of zooplank- 

 ton. The slope for fry is less than for yearlings 

 probably due to the smaller foregut capacity of 

 fry. Fry probably require a lower food concen- 

 tration to become satiated, and the number of 

 organisms per foregut may be approaching an 



Table 2. — Mean number of organisms per foregut and variance between samples by age group, area, and 



sampling period. 



357 



