Immobilization of Fingerling Salmon and Trout 

 by Decompression 



By 



DOYLE F. SUTHERLAND, Fishery Biologist 



National Marine Fisheries Service 



Nortiiwest Fisheries Center 



2725 Montlake Boulevard East 



Seattle, Washington 98102 



ABSTRACT 



Laboratory experiments revealed that some chinook salmon {Oncorhynchiis tsh<v- 

 wytscha) and coho salmon (0. kisutch) fingerlings are immobilized when decompressed 

 from atmospheric pressure to high negative pressures. About 69 S^^ of the chinook salm- 

 on were partially or completely immobilized at 71 cm of mercury vacuum, 48% at 61 cm, 

 17% at 51 cm, and none at 41 cm. The effects developed rapidly, peaking 5 min after 

 exposure. The coho salmon, in comparison, were less severely affected. Only 9% were 

 immobilized at 71 and 61 cm of mercury vacuum (reached 10 min after exposure), 2% 

 at 51 cm (5 min after exposure), and none at 41 cm. 



Studies (with coho salmon and rainbow trout [Salmo gairdneri] ) to determine the 

 effects of decompression within a turbine of a dam did not provide conclusive results. 

 However, some fingerlings caught in the tailrace immediately after their release in the 

 turbine intake were immobilized. Exposure to negative pressure below turbine runner 

 blades is one possible cause of immobilization. 



INTRODUCTION 



Many fingerling salmon and trout are injured 

 or killed by physical contact with turbines and 

 other structures within dams. Others are be- 

 lieved to suffer shock or death from severe pres- 

 sure changes encountered during passage 

 through dams (Schoeneman, Pressey, and Junge, 

 1961; Cramer and Oligher, 1964). Immobilized 

 fingerling salmon and trout have been observed 

 in turbine discharges of high and low dams on 

 the Columbia and Snake Rivers. The present 

 study, conducted in a laboratory and at Ice 

 Harbor Dam, was undertaken as a result of these 



observations and examines the role of decom- 

 pression as a possible cause of immobilization. 

 The Kaplan turbines at Ice Harbor Dam have 

 an area of low negative pressure below the blades 

 that theoretically averages about one-half at- 

 mosphere (38 cm of mercury vacuum) when the 

 turbines are operated at rated capacity." The 

 actual level of negative pressure below the tur- 

 bine blades is not known but must be consider- 

 ably greater than the 38 cm theoretical average. 



' Personal communication, S. Scott, U.S. Army Corps 

 of Engineers. 



