710 U. S. BUREAU OF FISHERIES I 



Recognizing that knowledge of the effect of preservatives in actual 

 fishing waters is essential for practical developments, various methods 

 have been employed which would serve for test purposes; due to per- 

 sonal factors, this phase of investigation has not been altogether 

 successful, but in the past season reasonably satisfactory tests were 

 obtained in fishing waters by mailing to cooperators, light wooden 

 frames containing twines covered with experimental preservatives, 

 the frames after a certain exposure being returned to Washington 

 for a test. While the number of preservatives tested by this method is 

 limited, the extension of knowledge of deterioration in various waters 

 is of great value. 



Experiments have demonstrated that among the best preservatives 

 for tiap nets are cuprous oxide, coal tar, mercuric oxide, and" copper 

 oleate. The proportions of these incorporated into the net appear to 

 depend upon individual localities. Coal tar is more effective in salt 

 water than in fresh water and also where tidal action is above noimal. 

 Cuprous oxide and copper oleate are most effective in qidet and in 

 fresh water. Under certain conditions, mercuric oxide is an excellent 

 preservative when used with coal tar; its cost is high and hence it 

 should be used only when necessary. More complete information 

 relative to the preservation of trap nets is contained in Fisheries 

 Document No. 1075. 



GILL NETS 



The study of the problem of obtaining longer service from gill nets 

 by the use of preservatives has been continued, and it has been demon- 

 strated that the use of the soluble portions of coal tar carrying fine 

 cuprous oxide has increased the life of the net up to 40 per cent. A 

 mixture of copper oleate and copper resinate has also proved effica- 

 cious. The former treatment produces a brown net and the latter 

 treatment a greenish net. The fishing power of the colored nets 

 appears to be equal to that of plain or untreated material. 



No preservative will prevent the damage to gill nets that is caused 

 by snags or by the present method of removing fish, although a sus- 

 tained mechanical strength, through the use of preservatives, should 

 lessen losses from these causes. Fishermen recognize that gill nets 

 should be thoroughly washed after use, but greater care should be 

 used in storage after drying. Direct sunlight is a powerful chemical 

 agent, and a gill net should be stored away from direct simshine as soon 

 as possible after drying. The deterioration of gill nets under certain 

 local water or atmosphenc conditions is extremely rapid and can not 

 be explained by the present methods of washing and drying which 

 Hre reasonably constant. It would appear that prevention of rotting 

 by the use of preservatives is essential and may be accomplished 

 when the causes of the rotting are better imderstood. Further in- 

 formation concerning the preservation of gill nets is contained in the 

 document referred to above. 



BY-PRODUCTS 



MENHADEN 



During the past year the bureau continued its technological study 

 of the menhaden industry. This industry has been given special 

 attention since it is typically representative of most of the oily fish 

 reduction industries, and certain of the information obtained should 



