PROGRESS m BIOLOGICAL INQUIRIES, 19 3 3 315 



As a logical extension of these " life history studies " investigation 

 relating to the growth and replacement of lish populations and their 

 fluctuations in abundance are finding increasing application with 

 respect to conservation and management of the great commercial fish- 

 eries, by yielding early evidence of depletion, should it occur, as a 

 safeguard to expanding industry ; and by predictions of future yields 

 as a direct aid in the orderly conduct of the fishing business. The 

 yield of the commercial fishery, and hence the success of a commercial 

 enterprise, is dependent upon the three major variables: Birth rate, 

 death rate, and migration. A " census " of the fish population upon 

 which a fishery depends, revealing the rate of replacement of the 

 stock, the occurrence of unusually successful spawning seasons, the 

 withdrawals from the stock by normal death rate or by commercial 

 fishing, together with additions or subtractions by the migration of 

 the fish themselves, forms the basis for successful predictions of sup- 

 plies available in future years. Hence, investigations of the commer- 

 cial fishery are designed to produce evidence of this sort, which has 

 great practical application in the protection as well as the wise use 

 of our fishery resource. 



As an aid to the work of artificial propagation of fish for restock- 

 ing interior, waters, studies are also conducted dealing with the pa- 

 thology and nutrition of fishes and with improvements in hatchery 

 technique and stocking practices. Moreover, aid to the water farmer 

 in the cultivation of shellfish is rendered by the development of im- 

 proved practices based upon a sound understanding of the natural 

 requirements of the organisms cultivated. 



In addition to these regular functions of the Division, various 

 projects were authorized at the end of the year to be carried out as 

 emergency work with funds from the Public "Works Administration. 

 These may be characterized as follows : 



1. Stream surveys and stream improvement in the national parks 

 and forests. Sixteen parties will spend periods ranging from 3 to 8 

 months in the field during 1934 in conducting physical and biological 

 surveys of selected areas in the national parks and forests of the 

 United States, distributed as follows : 4 in the Atlantic coast section, 

 9 in the Intermountain States, and 3 on the Pacific coast. The object 

 of these surveys is primarily to determine a rational and effective 

 policy of stocking these public watei-s with food and game fishes and, 

 secondarily, to render such aid and advice as is possible in the areas 

 under study to the United States Forest Service, for the purpose of 

 so changing or improving natural conditions as to increase the carry- 

 ing capacity of these streams and to facilitate natural reproduction 

 of fishes. 



2. A study of stream pollution in the Middle West, also financed 

 by the Public Works Administration. A corps of biologists, bio- 

 chemists, and engineers will be engaged for 1 year in studying the 

 effects upon aquatic life, either direct or indirect, of industrial and 

 trade wastes, domestic sewage, and river silt. Paralleling this inves- 

 tigation will be a further study by a part of the same staff of means 

 of utilizing, in the increased production of fish food and food and 

 game fishes, the nitrogenous wastes now" destroyed but of considerable 

 potential value and of isolating and neutralizing at their sources 

 toxic or harmful wastes resulting from industrial processes now lead- 



