376 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 47. — Shrinkage of pound-net and deep-trap-net twine following the application of tar or copper oleate 



as preservatives 



shrinkage produced by tar and by copper oleate. With both treatments measurements 

 made parallel with the selvage showed on the average 1/16 inch greater shrinkage than 

 did those made at right angles to the selvage. 



The data for individual nets showed a variation from "no shrinkage" to a maximum 

 shrinkage of 1 inch. It is this wide range of variation in shrinkage that makes the 

 designation of the legal minimum mesh in terms of "size as manufactured" so eminently 

 undesirable. The average shrinkage of meshes measured in this study was 7/16 inch or 

 slightly less than V<x inch. If it were known that the shrinkage of all nets closely 

 approximated this average, the designation of a legal minimum mesh size (as manufac- 

 tured) 1 4 inch larger than that intended for nets as found in use might prove reasonably 

 satisfactory. However, the wide range of shrinkage makes such a procedure impractical. 

 If the legal minimum mesh is to be defined "as manufactured," allowance should be 

 made not for the average observed shrinkage but for the maximum possible shrinkage. 

 A further objection to the designation of the legal minimum mesh size "as manufac- 

 tured" lies in the fact that illegal nets can be fished with impunity if they have been 

 treated before examination by a conservation officer. In other words, there is no exact 

 means of determining the original mesh size of a treated net. 



The conclusion is obvious that the most satisfactory method of designating mini- 

 mum legal mesh sizes of pound nets and deep trap nets is on the basis of mesh size 

 "as found in use." The wide experience of most commercial fishermen with different 

 kinds of webbing and preservatives is certainly sufficient to preclude excessive losses as 

 the result of undue shrinkage of their twine. 



SUMMARY 



1. The present investigation of the whitefish fishery of Lakes Huron and Michi- 

 gan was undertaken because of the threat to the whitefish stocks offered by the intro- 

 duction and rapid expansion in the use of a new and tremendously efficient gear, the 

 deep trap net. This net, which was developed in Lake Ontario, was introduced into 

 Lake Huron off Alpena, Mich., in 1928. Beginning in 1930, the use of the deep trap 

 net expanded rapidly throughout the State of Michigan waters of Lake Huron and 

 northern Lake Michigan. Operations with this gear were relatively limited in other 

 waters (Wisconsin waters of Lake Michigan; Indiana waters of Lake Michigan; 

 Michigan waters of Lake Superior and southern Lake Michigan). The greatest 

 development of the deep-trap-net fishery occurred in the Michigan waters of central 

 and southern Lake Huron. 



2. The investigation was carried out along the following general lines: 



a. A review of the available statistics on the production of whitefish in Lakes Huron 

 and Michigan over the period, 1879-1939. 



