FISHERY HTLLKTIN: VOL. 8«. NO. 4 



T = (P * N)/E 



(2) 



where T = total number of pink salmon eaten 

 P = total number of pink salmon in all 



stomachs examines 

 N = estimated total population of coho 



salmon, from Equation (1) 

 E = total number of stomachs examined. 



RESULTS 



The 3,000 tagged and marked pink salmon re- 

 leased at Marinelli Point on 26 April ranged in size 

 from 34 mm to 41 mm, with an average of 38 mm 

 (Table 1). A total of 57 juvenile sockeye salmon {On- 

 corhynchus nerka), 5 pink salmon, 2 chum salmon 

 (0. keta), 4 starry flounder (Platichthys stellatus), 

 1 sturgeon poacher {Agonies acipenserinus), and 210 

 yearling coho salmon were captured in the single 

 beach seine set done after the tagged fish were 

 released. All five pink salmon had been fin-clipped 

 and tagged. Three of these pinks had fork lengths 

 of 37 mm and the other two were both 38 mm long. 

 The two chum salmon had fork lengths of 41 mm 



and 40 mm. The four starry flounders and single 

 sturgeon poacher were all small and were imme- 

 diately released. All 210 coho salmon were measured 

 and their stomach contents examined for evidence 

 of predation on juvenile pink salmon. A total of 90 

 coho salmon had remains of fish in their stomachs, 

 including 51 pink salmon, 1 chum salmon, and 14 

 juvenile salmon that could be identified only as 

 either pink or chum salmon, due to extensive 

 digestion (Table 2). One additional coho salmon had 

 eaten two Pacific sandlance, Anmiodytes hexapterus, 

 but all other fish remains were too digested to 

 positively identify. Out of the 23 tagged pink salmon 

 found in the stomachs of these coho salmon, only 

 18 were sufficiently intact to permit measurements 

 of their fork length (Table 2). The average length 

 of these pink salmon was significantly less {t = 8.02; 

 P < 0.001) than the average length of the pink 

 salmon that were released (Fig. 2). Twelve of the 

 eighteen tagged and measurable pink salmon found 

 in the stomachs of the coho were clearly missing a 

 pectoral fin. The pectoral fins of all the other fish 

 were too digested to be certain whether or not they 

 had been fin-clipped. The average length of the 12 



Table 1 .—Characteristics of tagged juvenile pink salmon released in each experiment and those subsequently recovered by 

 beach seining. Nr = no. released; Ns = no. fish in prerelease sample; Min = minimum fork length; Max = maximum fork 

 length; X = mean fork length; C.I. = 95% confidence interval forX; Nc = no. of tagged salmon recaptured by beach seining; 

 H = no. hours after release of tagged fish. 



Table 2.— Number and size of juvenile salmon found in stomachs of predators in each experiment. Sets = no. 

 beach seine samples; S = no. of stomachs examined; N = total no. juvenile salmon in stomachs; Nc = no. of 

 tagged fish in stomachs; Nm = no. of tagged fish whose fork length could be measured; Min =_minimum fork length; 

 Max = maximum fork length; X = average fork length; C.I. = 95% confidence interval forX; JS = juvenile pink 

 or chum salmon. 



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