changes of as much as 70 pounds per square inch occurring 

 within thousandths of a second. These tests indicated that 

 cavitation effects in turbines are probably liarmless to fish. 



Changes in Flow 



Clianges in tlie flow of water hiyers adjacent to the inner 

 surfaces of a turbine intake may be a factor in guiding 

 fish. In the laboratory, a series of expanded steel plates 

 of diff'erent configurations were attached to the ceiling of 

 a simulated turbine intake (fig. 44). The configurations 

 modified the flow and velocity of the water in the vicinity 

 of the plates. After the plates were installed in a model 

 of a turbine intake, twice the average number of fish swam 

 into escape ports. The modification has potential applica- 

 tion at dams. 







!lT!."^r:^?r%V*'« 



FIGURE 44.— Expanded metal plate attached to surface of 

 horizontal conduit (in turbine intake model). The configura- 

 tions of the plate change water flow and may enable fish to 

 swim away from a turbine intake. 



GROUNDFISH OF THE CONTINENTAL SHELF 



Our biological studies of groundfish of the northeastern 

 Pacific Ocean began in 1964. The studies had four pur- 

 poses: (1) to determine the jiotential yield of stocks that 

 are only partially fished; (2) to devise methods to forecast 

 the abundance and availability of commercially important 

 species; (3) to find the maximum catches that can be taken 

 and yet maintain the stocks; and (4) to evaluate the 

 eff'ectiveness of conservation measures. Scientific infor- 

 mation was needed to protect the fishing rights of the United 

 States and for rational administration of national and in- 

 ternational fisheries. 



The immediate aim was to determine the maximum sus- 

 tainable yield of Pacific hake oft' Washington and Oregon. 

 At the same time, facts were gathered on the biological and 

 ecological relations of hake to other species. Plans were 

 made in 1966 for the investigation of ocean perch and sable- 

 fish (Anoplopoma fimbria) in cooperation with other agen- 

 cies. The major effort in 1967-68 was on hake in coastal and 

 inland waters (Puget Sound). Samples of hake were an- 

 alyzed for age, length, maturity, sex ratio, and weight (fig. 

 45). This material provided a basis for the coinprehensive 

 study of the biology, population dynamics, and eflfects of 

 fishing on hake stocks. 



33 



