believe that inclusion of this smaller size group of 

 walleye would not seriously alter our results or 

 conclusions as they relate to predation on juvenile 

 salmonids. They might, however, increase the im- 

 portance of shad in walleye diets. Walleye <200 

 mm FL will primarily be juvenile walleye and will 

 not reach 150 mm TL until mid-September (Brege 

 1981; Maule 1983). The length frequencies of 

 juvenile chinook salmon which we sampled 

 peaked at about 100 mm FL and, generally, 

 chinook salmon complete their emigration 

 by early fall (Raymond 1979; Sims et al. 

 1981). Juvenile shad, however, are generally 

 smaller than juvenile salmonids (Fig. 5) and emi- 

 grate in late fall (Stainbrook 1983). Whereas 

 juvenile salmonids may be buffered from the 

 juvenile walleye predation by a size and time sep- 

 aration, juvenile shad may become a more impor- 

 tant juvenile walleye food in late summer through 

 fall. 



This hypothesis is based on the current fish 

 abundances within the John Day pool of the Co- 

 lumbia River. Should these abundances change, 

 i.e., an increase in walleye abundance or a de- 

 crease in alternate prey, then we would expect a 

 change in the walleye-juvenile anadromous fish 

 interactions. The impact of walleye on the anad- 

 romous fish populations cannot be addressed 

 without adequate estimates of walleye and prey 

 fish abundances. 



Acknowledgments 



We thank Hiram Li and Carl Bond for their 

 reviews of the manuscript. Funds were provided 

 by the U.S. Army Corps of Engineers contract 

 DACW57-79-C-0067, the Oregon Agricultural 

 Experiment Station, and the Milne Computer 

 Center, Oregon State University, Corvallis, Oreg. 



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