174 



relationships. In 1994 th« National Marine Fisheries Service. 



initiated a study concentrating on water quality, primary 



productivity, and benthic invertebrates in shallow, littoral 



habitats of John Day Reservoir. (Ledgerwood and Grabowski 1995) . 



Similar studies with the additional objective of monitoring the 



nearshore fish cojninunity were initiated in Lower Granite Reservoir 



(Ledgerwood and Grabowski 1995; Bennett 1994). Primary objectives 



of these studies were to assess conditions prior to, during, and 



following proposed drawdowns in John Day and lower Granite 



reservoirs. Investigations of predator-prey related questions in 



» 

 the fish community have not been initiated for the John Day 



Reservoir. 



Monitoring the nearshore fish community of the John Day Pool 

 before, during, and after the proposed drawdown is important since 

 juvenile fall chinook salmon rear in these areas along with many 

 other species of resident fishes (both native and introduced) . 

 Physical changes resulting from drawdown may initiate disruptions 

 in the nearshore fish community and these disruptions may change 

 predator^ population structures and predator-prey relationships. 

 For instance, drawdown could influence year-class strengths of 

 predators if the aaount and suitaUsility of shallow littoral habitat 

 is reduced. Drawdown may also impact the non-salmonid prey of 

 predators, thus causing indirect impacts on juvenile salmonids. 



Predation by resident fishes is an important source of 

 mortality to juvenile salmonids in the Columbia River (Rieman et 

 al. 1991) . The northern squawfish Ptvchocheilus oreaonensis is a 



