PEARCY ET AL: DIEL FEEDING HABITS OF PACIFIC SALMON 

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10 



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 15 



10- 



5- 



SOCKEYE 



-CD 



[H 



Li. 



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cr 



UJ 



m 



PINK 



XH 



WW 



COHO 



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CHUM 



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35 40 45 50 55 60 65 70 



FORK LENGTH (cm) 



FIGURE 2. — Length-frequency histograms for the four species 

 of salmon caught in the 24-h study. 



ages are represented for sockeye and chum salm- 

 on. All pink and coho salmon were probably be- 

 ginning their second year of ocean life. Compari- 

 sons of length-frequencies between day (sets 1-4 

 and 10-12) and twilight and night (sets 5-9) were 

 not significantly different for sockeye, pink, and 

 chum salmon, but were significant for coho salmon 

 (Kolmogorov-Smirnov test, P < 0.05). Coho salm- 

 on were 2.4 cm larger in the twilight-night sets. 



Feeding Habits 



Stomach fullness of the four species of salmon, 

 calculated as a percentage of body weight, were 

 usually variable, ranging from 09c (empty) to a 

 maximum of 49c for sockeye, 3.09c for chum, 3.39c 

 for coho, and 2.39c for pink salmon (Fig. 3). Some 

 individuals of all species had empty stomachs dur- 

 ing most sets, regardless of time of day. Although 

 ranked differences of the stomach weight:fish 

 weight ratio were not significantly different be- 

 tween day (sets 1-4 and 10-12) and night-twilight 

 (sets 5-9) for each of the four species of salmon 

 (Mann- Whitney U-test, P > 0.05), the highest per- 

 centages of stomach weight to body weight for 

 sockeye (>39c) and coho and pink salmon (>2%) 



were obtained from nighttime sets (Fig. 3). 

 Moreover, our visual estimates of stomachs also 

 indicated that full, distended stomachs of sockeye, 

 coho, and pink salmon occurred only at night. 

 There were no suggestions of diel periodicity of 

 stomach fullness for chum salmon, however. 



The frequency of occurrence and percent com- 

 position of the most common prey taxa 

 (euphausiids, amphipods, squids, fishes) in the 

 cardiac portions of salmon stomachs containing 

 more than trace amounts of food are summarized 

 in Table 2. All species of salmon consumed all of 

 the four major categories of food. The most fre- 

 quently occurring major taxa was euphausiids in 

 sockeye and coho salmon, amphipods in pink 

 salmon, and "other taxa" (mainly salps, but often 

 unidentified material and sometimes pteropods 

 and polychaetes) in chum salmon stomachs. Am- 

 phipods were the second most frequent taxa in 



SET NUMBER 



4- 



3- 



2- 



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I 



0- 

 3- 



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I 



UJ 



Q 



o 

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1800 



" 0000 '|~0600 



SS SR 



TIME(hrs) 



1200 



FIGURE 3. Stomach fullness, expressed as a ratio of food 



weight to fish weight, for the four species of salmon caught in 

 each of the 12 gill net sets during the 24-h period. 



393 



