180 



John Day Pool. Collect environmental data 

 concurrent with sampling efforts. 



Rationale: Little information exists on fish 

 communities and community-level interactions in 

 Columbia River reservoirs. Information on fishes 

 within selected shallow littoral habitats of the 

 John Day Pool before, during, and after proposed 

 drawdown is important to our understanding of 

 habitat use and community composition in impounded 

 segments of the Columbia River. Drawdown could, 

 potentially affect reciuitment of both native and 

 introduced resident fishes, depending on habitat 

 requirements and the availe±>ility of suitable 

 habitat during and following the proposed drawdown. 

 The creation of impoundments and associated habitat 

 alterations have favored some native species such as 

 the northern squawfish and restructured fish 

 assemblages which now contain many exotic midwestern 

 species (Li et al. 1987). • Drawdown may establish a 

 new community equilibriiim through restructuring of 

 the current fish communities depending upon a 

 complex array of factors including pool-level 

 fluctuation, drawdown timing, and various 

 limnological effects. Monitoring these changes will 

 further our understanding of the potential effects 



