HARGREAVES: PREY PREFERENCE OF PREDATORS 



26- 



19 



cc 



5- 



b 



34 35 36 37 38 39 40 41 42 



FORK LENGTH (mm) 



Figure 2.— Size-frequency distribution of sample of tagged pink 

 salmon released in the first experiment (A) and all tagged pink 

 salmon subsequently recovered from stomachs of predators (B). 



fin-clipped fish was 35.4 mm, which is not signifi- 

 cantly different {t = 0.47; P > 0.50) from the aver- 

 age length of the 18 tagged and measurable pink 

 salmon. 



Pink salmon released in the second experiment 

 ranged in size from 36 to 51 mm fork length, with 

 an average of 44.4 mm (Table 1). A total of 1 juvenile 

 sockeye salmon, 1 juvenile chum salmon, 28 year- 

 ling coho salmon, 6 Pacific staghorn sculpin {Lep- 

 tocottus armatus), 10 Pacific herring (Clupea 

 harengus pallasi), approximately 500 larval walleye 

 pollack (Theragra chalcogramma), 20 Pacific snake 

 prickleback (Lumpenus sagitta), 1 red Irish lord 

 {Hemilepidotus hemilepidotus), 6 Dolly Varden 

 (Salvelinus malma), and 10 starry flounder were 

 captured in the 2 beach seine sets done before the 

 release. Examination of the stomach contents of all 

 the coho salmon, five staghorn sculpins, the red Irish 

 lord, and all the Dolly Varden provided no indica- 

 tion that any of these fish had recently eaten juvenile 

 pink or chum salmon. The seven additional beach 

 seine sets done on 6 June after the release of the 

 tagged pink salmon captured a total of 271 coho 

 salmon, 33 Dolly Varden, 46 staghorn sculpin, 2 

 coastal cutthroat trout {Salmo clarki clarki), 55 pink 

 salmon, and 3 chum salmon. Nineteen pink salmon 

 had been tagged (Table 1). All the untagged pinks 

 were larger. 



The stomach contents of 246 coho salmon, 14 

 Dolly Varden, and 16 sculpins were examined. There 

 was no evidence that any of the Dolly Varden or 

 sculpins had eaten any juvenile pink or chum salmon, 

 although one sculpin had eaten a juvenile coho 

 salmon. However, 13 of the coho salmon had eaten 

 a total of 17 juvenile pink salmon, of which 15 had 

 been tagged. The head was missing from one of the 

 two untagged pink salmon so it could not be mea- 

 sured, but the fork length of the other was 51 mm. 

 The tagged pink salmon found in the stomachs of 

 the coho salmon were typically the smaller ones (Fig. 

 3), with an average length significantly less {t = 

 5.06; P < 0.001) than the average length of all pink 

 salmon that were released in this experiment (Table 



2). 



No juvenile salmon were found in the stomachs 

 of predators captured on 7 June. A total of 1 juvenile 

 pink salmon, 141 yearling coho salmon, 1 Dolly 

 Varden, and 115 staghorn sculpins were captured 

 in 9 beach seine sets. The pink salmon was not 

 tagged and none of these predators had recently 

 eaten any juvenile pink or chum salmon. Five of the 

 coho salmon had been branded, so the estimated 

 total population of coho salmon in the vicinity of the 

 release site was 4,047, with a 95% confidence inter- 



14- 



10- 



cr 



LJ 



m 6 



-z. 

 2-1 



36 38 40 42 44 46 48 



FORK LENGTH (mm) 



50 52 



Figure 3.— Size-frequency distribution of sample of tagged pink 

 salmon released in the second experiment (A) and all tagged pink 

 salmon subsequently recovered from stomachs of predators (B). 



767 



