FISHING GEAR AND FISHING METHODS 275 



the amount they receive for their fishery products, the means of increasing the 

 hfe of netting is a matter of paramount importance. 



The use of various preservatives which date back many centuries continues to- 

 day for the following reasons: 



1. Protection against mechanical wear and tear, resulting from the rubbing 

 (abrasion) of the threads against one another, the floats and leads, the sides of 

 the boat, the drag on the ocean floor, etc. 



2. Protection against the action of microorganisms. 



3. Protection against oxidation, resulting from the storage of the nets while 

 wet or covered with fish oils and blood and slime. 



4. Protection against fiber-tendering effects when exposed in strong sunlight 

 after cleaning or during drying periods. 



Cutching and so-called "tanning" of nets is among the oldest known methods 

 of preservation. Cutch, also known as "catechu" and "querbracho," is a general 

 term applied to the boiled down, aqueous extract of the bark, wood, or leaves of 

 various trees or plants, ranging from such tropical forms as the acacia tree of 

 India to the birch, hemlock, or pine of temperate climates. These materials in 

 extract or dry bark form continue to be used today, but are far less popular than 

 formerly. The general conclusion appears to be that such treatments are not very 

 eflBcient. The protective action is of such short duration that frequent retreatments, 

 involving costly labor and time, are necessary. 



The use of tar for the preservation of nets dates back almost as far as the use 

 of cutches. Products such as coal tar, pine tar (wood tar), and creosote have been 

 widely used for many years. Although still in use today they are being replaced 

 by modern chemical preparations. 



Tar was originally applied to nets because its action tends to glue the fibers 

 together, thereby increasing their strength as well as waterproofing them to some 

 extent. However, the resulting stiffness and the increase in weight were unfavor- 

 able factors. The rigidity of the net caused it to wear out mechanically; after 

 several applications the net often gives way at the knots. Because the tar must 

 be heated to relatively high temperatures, the nets were often burned or tendered 

 (weakened). Thinners are sometimes added to overcome the necessity for heating, 

 but this is not too satisfactory. The use of tar is also attended by certain dangers 

 to those who come in contact with it, particularly the poisoning from "tar dust" 

 which collects on dried tarred netting during winter storage. 



Early scientific studies showed that the deterioration of a net was due prin- 

 cipally to the fact that microorganisms consume the cellulose which constitutes 

 95 per cent of the fibers. On this theory metallic compounds were first introduced 

 in the form of copper sulfate, better known as "bluestone." After widespread 

 use, both here and in Europe, it was discovered in 1930 that bluestoning had no 

 prolonged effect, although it did act as a deterrant to bacterial growth if used 

 often enough. 



It was at about this time that copper oleate and copper naphthenate were in- 

 troduced since they were found to be more effective as preservatives. However, 

 these products tended to leach out rather quickly. In recent years copper naph- 

 thenate has almost entirely superseded copper oleate as it is more stable and 

 better adapted to marine uses. It is now the principal toxic ingredient in most 

 of the net preservatives. That such products are far from being perfect is best 



