FISHERY INDUSTRIES OF THE UNITED STATES, 1931 109 



NET PRESERVATION 



As a result of the bureau's work on net preservation conducted by 

 W. T. Conn a method of protecting hcavj'- nets, such as traps, pounds, 

 f3'kes, and seines, from deterioration has been developed. This 

 makes use of toxic dyes applied to the thread or net. When these 

 are used in connection with a specification coal tar, the tensile strength 

 of exposed cable cotton has been extended beyond a degree previously 

 thought possible. Specifically, tensile strength of 15-thread cable 

 cotton, so preserved, increased constantly in all tests, during the 

 season of greatest deterioration, between June and December. 

 Crj'stal violet is considered the best dye for this service, but malachite 

 green and thioflavine-S have proven only slightly inferior. Sources 

 of supply of this dyed twine are now established and are available for 

 prospective buyers. 



A study of tars used for preserving nets has shown that many tars 

 are of an inferior quality for net preservation. With the aid of the 

 above test and through developmental work with tar it has been possible 

 to prepare a tar which has maximum preservative qualities. Speci- 

 fications for this net preservative tar have been drawn up, for the 

 first time as far as known, and supplies of this specification coal tar 

 certified for quality by the manufacturer are now available to 

 fishermen. 



While the above application prevents deterioration and preserves 

 tensile strength, it does not entirely eliminate weed growth on the 

 net. It is possible to retard this weed growth or fouling by adding 

 certain copper compounds to the coal tar dip applied to dyed twine. 

 The reduction of fouling, however, is effected at some sacrifice to 

 tensile strength. 



Studies also were continued on developing formulae for preserving 

 light nets such as gill nets, trammel nets, and the like. As a result of 

 this the value of copper oleate and chicle as preservatives, as previously 

 reported, were confirmed. In addition, tung and pine oils were found 

 to have value as preservatives for Light nets. 



While certain preservatives have been efficacious in prolonging the 

 fife of fight nets, an investigation on gill nets fished by a vessel out of 

 Portland, Me., during the summer of 1931, has shown that many 

 nets in this type of fishery deteriorate because of improper cleansing 

 and storage. This deterioration can be retarded to a great extent 

 by washing the net with lime water as soon as possible after each fish 

 haul, and rinsing with clear water. The net should be removed from 

 the reel as soon as dry, as direct sun rays injiu*e the dry fabrics. A 

 boxed damp net should never be covered, and when nets are to be 

 stored they should be thoroughly cleansed, dried, and suspended in 

 dry, well-ventilated shade. 



Information obtained during research upon the preservation of 

 fish nets indicates that the useful life of rope may be extended with 

 comparatively fittle expenditure of time and money. It is possible 

 that the toxic dye treatment described above for fish nets may be of 

 value in this connection. However, it has been demonstrated by 

 laboratory test that the dye must be applied to the hemp before the 

 yarn is laid. Experiments in this direction have been made possible 

 through cooperative research between this bureau and the Bureau 

 of Construction and Repair, Navy Department. Preparation of 

 test material is in progress at the naval rope factory at Boston, Mass., 

 under personal direction of a technologist from this bureau. 



