PROGRESS IN BIOLOGirAL INQUIRIES, 1935 417 



natural mortality, was not sufficiently abundant to maintain the 

 catch on a high level of abundance. 



With the spawning areas contributing to each feeding area known, 

 it will be possible to estimate the abundance, and the size composition 

 of the catch to be expected during the following season, by sampling 

 the age composition of the spawning population during the spring. 

 Thus, for the Sitka population, unless the new recruits entering as 

 4-year-olds in 1936 are relatively very abundant, the present low 

 level of abundance may be expected to continue. This information 

 will prove invaluable in providing for a stabilized fishery by permit- 

 ting the formulation of regulations to spread the fishing intensity 

 over the populations best able to withstand the strain. 



INVESTIGATION CONCERNING THE PROTECTION OF MIGRATORY FISH AT THE 



BONNEVILLE DAM 



Satisfactory progress has been made in the problem of providing 

 suitable fishways at the Bonneville Dam. The w^ork has continued 

 under the direction of Harlan B. Holmes, assisted by Henry F. 

 Blood, both of whom have had the temporary assistance of other 

 biologists and engineers. The w^ork has been conducted in close 

 cooperation with the staff of United States Engineers and the State 

 fish and game departments. The program and results of the first 

 year's activities are briefly related in Progress in Biological Inquiries, 

 1934. 



Formal recommendations were submitted to the War Department 

 by the Commissioner of Fisheries in August 1934. After prolonged 

 consideration the War Department approved a plan of fishways 

 that for the greater part followed the recommendations of the Com- 

 missioner of Fisheries. Some features that the Bureau's staff had not 

 considered essential were added. Tlie collecting systems for attract- 

 ing and directing the fish to the fishways in the main channel were 

 materially reduced. 



The detailed designing of the fishway is being done by the staff of 

 United States Engineers. The staff of the Bureau of Fisheries has 

 remained in close contact witli tlie Engineers, and has found occasion 

 to offer suggestions. 



The progress of construction of the dam has been carefully fol- 

 lowed with the view of assuring the free ]3assage of fish during 

 the period of construction. Although the skeletal structure of the 

 powerhouse, which obstructs one channel of the river, and the base 

 of one-half of the spillway dam, which will obstruct the main chan- 

 nel, are nearing completion, as yet there has been no interference with 

 the passage of fish. It was anticipated, however, that temporary 

 fishways will be required during the latter stages of construction. 

 A study of the anticipated condition has been made and temporary 

 fishways have been designed. 



An extensive study was made of the injury to fish in passing 

 through water turbines. Preliminary results of the investigation 

 indicate that there is a tremendous variation in the conditions pre- 

 sented by different plants, w4th the result that some certainly could 

 not be passed by even the smallest fish, whereas others may cause 

 little or no injury. The Bonneville turbines are judged to approach 



