XXII REPORT OF THE COMMISSIONER OF FISHERIES 



Experiments in the artificial propagation of mussels were con- 

 tinued, and progress was made in perfecting tlie use of hatchery 

 troughs for this purpose. An investigation bearing on the rela- 

 tionship between fish slime and the attachment of tlie larval mussels 

 to the fish on which they are parasitic during the .early stages of 

 their development was undertaken by Dr. M. M. Ellis, of the Uni- 

 versity of Missouri, and promises to yield results of the greatest 

 importance to the success of the experiments in artificial propa- 

 gation. 



ALASKA CLAMS 



The utilization of the clam resources of Alaska has been of recent 

 development but already there is ample evidence of the serious 

 depletion of some of the most productive beds. An investigation 

 of these resources and of the biology of the clams was begun during 

 1923 and continued during the past year. Surveys were made of 

 the beds in the region around Cordova and at Kukak in Shelikof 

 Straits. Observations were also made on other mollusks in Alaska 

 and on certain of the beaches in the State of Washington. Age deter- 

 minations were made and the rate of growth determined for several 

 localities, and data were secured on the time of spawning and its 

 relation to water temperature. Many data showing the relation of 

 size and age to sexual maturity have been worked out, making 

 possible the determination of proper size limits. 



These investigations have shown that Alaska clams grow much 

 more slowly than do the clams on the coast of Washington, requir- 

 ing about twice as much time to reach a marketable size. At Cor- 

 dova, Alaska, a length of 41^ inches is attained in about 6 years, 

 while at Copalis, Wash., only 3 years are required. 



The Washington clam beds were found to be much more heavily 

 seeded than those of Alaska. In 1923 the set of small clams at 

 Copalis averaged over 1,400 per square foot, but in Alaska the 

 average number of small clams in 1923 and 1924 was less than one 

 per square foot. 



Clam canning was begun in the Cordova district in 1916. An 

 analysis of about 150 clams taken showed that over 100 of them 

 were young when canning began eight years before. Under such 

 conditions it is patent that the fishermen are drawing heavity on their 

 capital stock, and the need for regulation is evident. A size limit 

 of 41/^ inches has been placed on all the Alaska beds to reduce the 

 intensity of digging and thus ji re vent depletion. A report has been 

 published giving the results of the investigations made during 1923 

 and 1924. 



INVESTIGATIONS RELATING TO FISH CULTURE 



The importance of artificial propagation as an aid in the con- 

 servation of our fishery resources is generally recognized. In addi- 

 tion to the extensive fish-cultural operations conducted by the bureau, 

 nearly all of the States and many private agencies maintain hatch- 

 eries for the purpose of stocking their waters with food and game 

 fishes. The biological principles involved in artificial propagation 

 are not yet thoroughly understood, and difficulties frequently arise 

 which demand study that can be given only by a competent biologist. 

 In pond culture a knowledge of pond ecology is essential if the work 



