42 U. S. BUREAU OF FISHERIES 



the catoli to the size of the net mesh. The mesh sizes of tlie nets 

 studied ranged from 2% to 2'^^/iq inches. On the basis of the 1937 and 

 earlier (1927-28) gill net studies, the Bureau will reconnnend a 

 definite mesh size for gill nets used for all species commonly taken 

 in small-meshed nets, and will recommend also an upward revision of 

 the present legal size limits for blue pike-perch and saugers in order 

 to provide better protection for spawning females. It is not antici- 

 pated that the recommendations will differ materially from those 

 made by the Bureau at an earlier date. 



Another phase of the gill net investigations was the experimental 

 study of the shrinkage of gill net twine. The adoption of the flexible 

 steel rule, developed by the National Bureau of Standards, and the 

 further legal provision that net mesh must measure full size at all 

 times, whether new or old, wet or dry, caused considerable controversy 

 over the allowance which should be made for shrinkage in ordering 

 new netting. At the request of the fishermen, who provided the neces- 

 sary materials, experiments are being conducted to determine the 

 maximum shrinkage, rate of shrinkage, and the relative importance 

 of water and of several preservatives in inducing shrinkage. 



The differences among various methods of measuring- gill-net 

 meshes (stretched measure, 1 pound strain on 1 mesh, 1 pound strain 

 on 3 meshes, 8 ounce strain on 1 mesh, and National Bureau of 

 Standards flexible rule) are being determined expenmentally. This 

 information will be submitted to the fishermen and conservation 

 officials of those Great Lakes States that have recently adopted the 

 flexible rule as the legal method for determining the size of gill nets. 



SHELLFISH INVESTIGATIONS 

 Dr. Fatjl S. Galtsoff, in cliar<je 



Oyster fishing continues to occupy a prominent position ainong 

 the fishery industries of the country in spite of serious handicaps 

 caused by the ever increasing depletion of natural oyster beds, de- 

 struction of valuable oyster bottoms by pollution, and depredations 

 by natural enemies of the oyster. Dissemination of knowledge re- 

 garding the life history of the oyster has resulted in wider recogni- 

 tion of the fact that a system of oyster cultivation is necessary for 

 maintaining the productivity of present resources. 



Since success in the cultivation of oysters depends on knowledge 

 of local conditions and good judgment in applying to them the basic 

 principles of oyster culture, the shellfish investigations of the Bureau 

 of Fisheries are conducted along the following lines: physiological 

 studies, dealing primarily with the propagation and nutrition of oys- 

 ters; ecological investigations, which provide answers to questions 

 regarding the suitability of various waters to oyster culture; pro- 

 tection o^ oyster bottoms against starfish and other enemies; and 

 investigations of the effect of trade wastes on oyster bottoms. 



The first line of attack supplies the basic knowledge concerning 

 the requirements and activities of the oyster which is essential for 

 the practical oyster grower. Ecological observations made in 1937 

 in Long Island' Sound and in the inshore waters of Virginia, North 

 Carolina, Alabama, and Florida have been of gi-eat value to State 

 authorities and private oyster organizations in transplanting seed 



