232 U. S. BUKEAU OF FISHERIES 



greatly depleted. The number of diggers had increased, but the 

 catch per man was lower than the average of recent years. All sizes 

 of clams were taken, but the class of 1923 (4 yesLVs old) composed 

 over half of the total. The pack of the Alaska canneries was below 

 average, due partly to economic conditions. Examination of the beds 

 indicated that they support only small, slow-growing clams. 



Data on the change in body proportions and weight during the life 

 of the clam were collected. The clams are nearl}^ circular in the 

 early adult stage, but Avhen 4 centimeters long the width is but 35 

 per cent of the length. The width increases gradually throughout 

 life, that of large clams averaging 42 per cent of the length. Study 

 shows that there are slight differences in growth in the two sexes. 



As a result of these studies, the clam industry in Alaska has been 

 regulated more wisely and reconunendations for the protection of 

 the beds have been offered to the fisherj^ authorities of the State of 

 Washington. 



ALASKA SHRIMP 



AVith the cooperation of Warden Frank Hj^nes, Doctor Weymouth 

 and Mr. McMillin made a preliminary investigation of the shrimp 

 industry at Petersburg, Alaska. Over 20 species were obtained on 

 the summer trawling grounds. A similar collection made in winter 

 should increase this number, as the work is carried on at different 

 places and depths. In summer the daily catch is limited arbitrarily 

 to ten 200-pound boxes per boat, as this amount Avill supply the 

 summer markets. Although unrestricted fishing is carried on in- 

 tensively during the winter, the catch per boat has not declined since 

 the beginning of the fishery. Trawls can be operated on compara- 

 tively smooth bottom only. Such places are of small extent and 

 difficult to find. Therefore, the actual fishing area covers only a 

 small part of the range of the shrimp, and depletion is not to be 

 expected. 



FRESH-WATER MUSSELS 



During the past year the bureau's investigations on the fresh-water 

 mussels of the Mississippi River Valley have developed along new 

 lines that promise practical results as valuable as any attained here- 

 tofore in this field. One notable achievement has been the develop- 

 ment of methods of artificial propagation of the species most valu- 

 able to the button manufacturers, and another has been the study of 

 rates of growth by precise methods that make possible a careful 

 check of the effects of environment on growth, an important step in 

 the development of sound methods of mussel farming. 



In nature, mussel glochidia are parasitic on the gills of certain 

 species of fish, Avhere they undergo metamorphosis and are distributed 

 by falling from the fish when the proper stage of development is 

 reached. Those that fall by chance in favorable localities survive, 

 but countless numbers perish. In 1926 Dr. Max M. Ellis, special 

 iuAestigator for the bureau, succeeded in carrying individual glo- 

 chidia through the same metamorphosis in a nutrient solution, in 

 which larva» developed successfully from normally parasitic organ- 

 isms to free-living young mussels able to exist on river bottoms. 

 These experiments were repeated in the summer of 1927 at the Fair- 



