120 U. S. BUREAU OF FISHERIES 



addition to the accelerated exposure at Beaufort, N. C No special 

 attention has been given to the yearly variability as this has been 

 previously recognized. It was noted, however, that due to local 

 drought conditions the fouling of nets in Chesapeake Bay was excep- 

 tionally heavy in 1930. The deterioration of nets appears to be 

 primarily influenced by currents, depth of water, character of bottom, 

 concentration of bacteria, salinity, and temperature. The work of 

 1930 was divided between trap netting and gill netting since these 

 are not only important classes of nets in themselves, but are typical 

 of most of the other nets in the matter of preservation. 



TRAP NETS 



These represent the nets that must be exposed in water for long 

 periods. They must be strong to withstand storms and rough han- 

 dling, and hence are made of heavy cotton. It is desirable that the 

 webbing should be flexible, resistant to abrasion and marine growths, 

 and yet be as light as possible. During 1930 these ideal conditions 

 were approached by several preservatives. The principle of impreg- 

 nating the twine with a light chemical mixture and covering this 

 with a heavy mixture appears to have been established as highly 

 beneficial. 



Copper oleate, when used in combination with other materials, 

 continues to be very efficacious, especially in fresh water. Coal tar 

 is still an essential component in the most desirable trap preservative 

 formulae. The fishermen suffer heavy losses due to inferior tars, and 

 a high grade standard quality is greatly needed. 



GILL NETS 



Exposures of gill-net thread were made in representative waters 

 in 1930 and at the Reedville (Va.) laboratory. Extensive work was 

 carried on in which the small gill nets were operated to reproduce 

 on a laboratory scale the service of commercial gill nets, except that 

 the catch of fish was kept at a minimum. By this means informa- 

 tion was gained concerning comparative deterioration of cotton, silk, 

 and linen, the effects of preservation on webbing, and certain effects 

 of chemical washing. The most important fact demonstrated was 

 that the deterioration of a gill net by the direct rays of the sun is 

 much more destructive than water exposure for the same length of 

 time. A certain chemical was proven to be highly efficacious in 

 resisting the destruction caused by the rays of the sun. 



Much data on these classes of twine were obtained through the 

 assistance of fishermen and other cooperators, who exposed small 

 mailable samples, which were afterwards returned to Washington for 

 inspection. Tliis principle of obtaining infoiTnation regarding special 

 fishing waters may be of considerable future value. 



NUTRITIVE VALUE OF MARINE PRODUCTS 



Marine products represent an important source of food. This 

 class of foods, generally speaking, is a good source of proteins, vita- 

 mins, and minerals in quantity and variety. Because of these facts 

 and because the primary consideration of food products is their food 

 value, the Bureau of Fisheries has become greatly interested in the 

 science of nutrition. 



