P150GKESS IN BIOLOGICAL IXQUIRIKS, 1929 1071 



oiniiiendatioiis have bern foniiulated for iinproviii*^ commercial fish- 

 in*^ gear in order to avoid undue \vasta<;e of" immature and undersized 

 fish cau<^ht ordinarily aloiiir with majketahh' sizes. In the Pacific 

 Nortiiwest i)ractical methods hav<' been developed for scivening 

 the mouths of irrigation ditches and j)ower-(liversion canals to ])i'e- 

 vent the tremendous losses of young migrating salmon from follow- 

 ing the downstream currents into the irrigation ditches, or protecting 

 them from injury and destruction by power-house equipment. The 

 prevention of such waste is a positive means of conservation, and 

 progress in these lines is most encouraging. 



The work of the investigators in a(|uiculture has continued to yield 

 j)ractical and valuable results. As a culmination of several years' 

 experiments on tront culture, Document lOGl. Care and Diseases of 

 Trout, ap])eared late in the year. This publication, although based 

 on painstaking scientific work, presents the information of value to 

 the trout culturist in such simple and practical terms that it has 

 received nnich enthusiastic praise from fish culturists at home and 

 abroad. Progress has also been made in increasing the production 

 of the wai'ui-water pond fishes, such as largemouth bass and crappie, 

 and in understanding the factors regulating the production of fish 

 food in pond areas. 



Mollusks, being stationary, are peculiarly adapted to successful 

 farming, and marked impi'ovements have been made by the bureau's 

 investigators in oyster-cultural methods. These are rapidly being 

 adopted by the oyster producers of both coasts. In fresh-w^ater 

 mussel culture numerous difficulties involved in the method of arti- 

 ficial propagation described in the previous report have been solved, 

 and methods of large-scale production are being developed. As a 

 result of these advances the old method of mussel propagation by 

 the inoculation of stranded fishes in the Mississippi River has been 

 abandoned as being of doubtful efficacy. The prospects for early 

 rehabilitation of the mussel fishery in the upper ^Mississippi River, 

 however, are uncertain because of the increasing menace of pollution. 

 Plans are under way to give to the problems of river pollution during 

 the coming year the attention that the gravity of the situation 

 warrants. 



Investigators of the division of scientific inquiry have continued 

 to participate in the activities of the North American Committee on 

 Fishery Investigations, an international body formed for coordinat- 

 ing investigations of the fisheries of the North Atlantic coastal and 

 high sea areas. At a meeting held October 15 and 16, 1929, at 

 Ottawa, Canada, representatives of Canada and the United States 

 were jjresejit and gave extensive consideration to problems of fishery 

 investigation of the cod, haddock, mackerel, and other fishes of eco- 

 nomic importance, as well as certain oceanographical investigations 

 of the region having international interest. Attention was given to 

 the possible effect on the fisheries of the proposed damming of 

 Passamaquoddy Bay, a subcommittee being appointed to examine the 

 conditions of that area, to consider the plans of the company pro- 

 posing to develop hydroelectric power, to study all available informa- 

 tion bearing on the predictable effects of the project on the fisheries of 

 the region, and to report findings to the two Governments. A meet- 

 ing of this connnittee was held December 12. 1929. A report was 

 rendered and recoimnendations offered for a more thorough investi- 



