FISHERY BULLETIN: VOL. 81, NO. 4 



> 



LU 



a. 



SUMMER 1980 



Upper 

 pelagic 



Lower 

 pelagic 



Upper 

 intertidal 



Lower 

 intertidal 



FIGURE 4. — Principal prey items of juvenile salmonids and commonly associated nonsalmonids cap- 

 tured in four habitats of the Columbia River estuary during summer 1 980. A principal prey item has an 

 IRI value > 50; the prey item with the highest IRI value for each species is indicated by a solid circle. 

 Number of stomachs examined is shown in parentheses. 



that could prey on salmonid species. Dunford (1975, 

 cited by Levy and Levings 1978) found Pacific 

 staghorn sculpins feeding on salmonids. 



Our sampling gear was less effective for capturing 

 adults than juveniles; however, we feel that our sam- 

 ples indicate the relative importance of the various 

 sized fish in the estuary. Larger fish, i.e., adult 

 salmon, steelhead, and American shad, may have 

 swum under or around the sides of the purse seines as 

 we were sampling. Another possible sampling bias, at 

 least in the lower estuary, was the tidal stage at which 

 we sampled. Beach seining was not generally done at 

 high tide because it was impractical due to beach con- 

 figuration. Possibly more salmonid predators move 

 into mixed intertidal areas during high tide. Even 

 with all the possible biases, if there were any large 

 populations of predators of juvenile salmonids in the 



estuary, we should have caught more than we did. 

 The logical conclusion is that the estuary represents 

 a sanctuary from fish predators for juvenile sal- 

 monids. 



The food habits of salmonids differ from estuary to 

 estuary. Unlike the Columbia River estuary where C. 

 salmonis and Daphnia spp. were the primary prey, 

 Myers (1980) found fish to be the primary prey for 

 juvenile chinook and coho salmon in Yaquina Bay, 

 Oreg. Although C. salmonis was important prey in the 

 Sacramento- San Joaquin Delta, Neomysis mercedis 

 was also important for juvenile chinook salmon 

 ( Sasaki 1 966) . In the Squamish River estuary, British 

 Columbia, N. mercedis and Anisogammarus (— 

 Eogammarus) confervicolus were the primary prey 

 for juvenile chinook and coho salmon (Levy and 

 Levings 1978). In the Sixes River estuary, Oreg., C. 



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