1096 U. S. BUREAU OF FISHERIES 



exists in these localities at the present time. In those localities which 

 the scientists were not able to visit during the summer, series of sam- 

 ples were taken and preserved in formalin by the bureau's patrol 

 service. 



RAZOR CLAMS 



As long as the razor clam industry retains its present value, cer- 

 tain facts must be gathered annually, that they may be made avail- 

 able for future comparison and that they may serve as an index to the 

 condition of the beds. A general survey of the industry including 

 the intensity of digging, the area being exploited, and the age of the 

 clams in the commercial catch, is essential. 



During the season of 1929, observations were confined to the vicinity 

 of Cordova, where the most important Alaska fishery is located. 

 Statistics designed to show the intensity of fishing have been gath- 

 ered, and a study is being made of the age composition of the com- 

 mercial catch in order to detect evidence of depletion. New collec- 

 tions of shells from the bars were made by Seton Thompson, and 

 a part of them have been measured and recorded, under the direction 

 of Dr. F. W. Weymouth of Stanford University, with the intention 

 of comparing the growth rate of the clams on different bars in that 

 locality. 



CONSEBVATION OF FISH BY MEANS OF SCREENS AND LADDERS 



The investigation on the conservation of fish by means of screens 

 and ladders was begun in 1928 and continued in 1929 under the direc- 

 tion of Shirley Baker, consulting engineer, assisted by U. B. Gilroy. 

 The purpose of this investigation is to develop and install mechan- 

 ical and electrical devices which will prevent fish from entering 

 irrigation ditches. Enormous numbers of fish, chiefliy salmon, which 

 have entered these ditches, are killed each year when the ditches are 

 dried up at the end of the irrigating season. 



The activities under this investigation during 1929 were as follows : 

 (1) The construction and operation of six electric fish screens on 

 waterways of major importance, together with extensive experi- 

 mentation on tliese devices for the purpose of simplifying and im- 

 proving them; (2) the installation of a mechanical revolving fish 

 screen; (3) the installation of a large concrete fish ladder; (4) 

 studies of models and designs of fish ladders as well as the speci- 

 fications for the fish ladders required at a number of locations; 

 (5) analysis of the effects of five major hydroelectric developments 

 proposed for the Northwest with the specifications of the necessary 

 structures required for fish protection; (6) study of the practice of 

 the Canadian Government in the matter of fish ladders; and (7) 

 miscellaneous services rendered to State commissions and commercial 

 bodies in the interest of fish conservation. 



MECHANICAL FISH SCREENS 



The most practical and economical type of mechanical fish screen 

 is the one that has been adopted by the Oregon Game Commission 

 and the Washington Division of Fisheries. This screen consists 



