FISHERY BULLETIN: VOL. 84, NO. 4 



100* 



Percent Stomachs Mostly Full/Empty 



75* 



c 



V 



o 



1_ 

 V 



0- 



50* - 



25* 



0* 



Stomochs less than 25* full 



54 



40 



80 



31 



30 



25 



59 



50 



15 



34 



— i 1 1 1 1 1 — 



10 11 12 13 14 15 

 Time (hours) 



16 



17 



18 



19 



Figure 3.— Diel pattern of stomach contents of Pacific hake as demonstrated by percent 

 of stomachs <25% full (upper curve) and >75% full (lower curve). Three-point moving 

 average used to smooth the curves. Sample sizes shown above x-axis. 



is a weak indication that these fish exhibit a pattern 

 of feeding more heavily at night than during the day. 

 For a predator feeding nocturnally, the expected 

 pattern of this curve would be low percentages of 

 empty stomachs early and late in the day, and high 

 percentages of empty stomachs at midday. No tows 

 were made between the hours of 2000 and 0700 thus 

 direct evidence of nocturnal feeding was not avail- 

 able. 



Comparison of stomach contents by size class 

 showed the greatest amount of variation (Table 3, 

 Fig. 2b) because of the shift in diet composition from 

 euphausiids in early life stages to fishes in later 

 stages. 



The estimated consumption by Pacific hake in the 

 Columbia statistical area over all prey categories is 

 4,651 t/d (Table 4). The amount of euphausiids con- 

 sumed (over 4 kt/d), exceeds that of all other prey 

 categories combined, but several commercially 

 valuable species are also consumed in significant 

 quantities. Consumption of pink shrimp is estimated 

 at over 9.2 t/d, and almost 120 t/d of herring are 

 consumed. Residence time for each size class of 

 Pacific hake was derived from data presented by 



Francis (1983) (size class 1: 80 d; size class 2: 69 d; 

 size class 3: 45 d; size class 4: 42 d; and size class 

 5: 41 d) to extrapolate estimates of annual prey con- 

 sumption from the daily consumption rate in the 

 Columbia area. The annual consumption of pink 

 shrimp, based on these data, is estimated at 659.3 1. 



Pacific Hake-Pink Shrimp Interaction 



The regression of Pacific hake CPUE versus pink 

 shrimp CPUE resulted in a nonsignificant correla- 

 tion (r 2 = 0.114, df = 15, P = 0.185). However, 

 the regression performed with a 2-yr lag (hake 

 CPUE in year i versus shrimp CPUE in year i + 

 2) showed a significant negative correlation between 

 the variables (r 2 = 0.418, df = 15, P = 0.005). 

 Note that the significance of the latter analysis 

 stems largely from data obtained in recent years 

 (Fig. 4). 



DISCUSSION 



One of the most striking patterns found in the data 

 is the distinct change in diet composition that Pacific 



952 



