WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 375 



young whitefish tagged in Lake Michigan were later recovered (Smith and Van Oosten, 

 1940) 39 suggests that they successfully withstand careful handling. 



Our field investigators reported that almost all deep-trap-net fishermen were ex- 

 tremely careful in the sorting of the catch. To be sure, they may have been more than 

 ordinarily painstaking when the investigators were aboard their craft. Nevertheless, 

 most of them appeared to be following a well established routine that involved a min- 

 imum of handling of illegal-sized whitefish and a minimum length of time out of the 

 water. Only one fisherman was observed whose method of sorting was considered likely 

 to result in the death of a high percentage of the undersized whitefish. 



The fact that the illegal whitefish taken by the deep trap nets in Lakes Huron 

 and Michigan were so near the legal size increased greatly the potential harm resulting 

 from the destruction of undersized individuals. It was estimated that practically all 

 of the illegal-sized whitefish observed would have attained the legal weight of 2 

 pounds within another year, as their average weight at capture was 1 pound, 9.7 ounces 

 (17.6 inches, total length). However, the illegal-sized whitefish from the pound nets of 

 Lake Huron (no data from Lake Michigan pound nets) were relatively small (13.1 

 ounces and 14.1 inches, total length). 



SHRINKAGE OF THE TWINE IN POUND NETS AND DEEP TRAP NETS 



The fact that pound-net and deep-trap-net twine is treated regularly (usually in the 

 spring of each year) with tar or copper oleate as a preservative gives rise to a troublesome 

 question as to whether the minimum legal size of the mesh shall be designated "as found 

 in use" or "as manufactured." It is well known that the application of a net preserva- 

 tive to cotton twine is almost always accompanied by some shrinkage. However, the 

 exact extent of this shrinkage is not predictable for individual nets. The amount of 

 shrinkage of the twine varies with the method of applying the treatment, the number of 

 times the webbing is treated, the nature of the webbing as received from the manufac- 

 turer, and possibly with the type of preservative employed. If the minimum legal mesh 

 size is defined "as found in use," honest fishermen conceivably might find themselves 

 confronted with the problem of large amounts of expensive gear rendered useless by un- 

 expected high shrinkage. On the other hand, if the minimum mesh size is defined "as 

 manufactured," unscrupulous fishermen may so control the type of twine purchased and 

 the method of preservation as to shrink the mesh to a -uze far below the intended legal 

 minimum. Regardless of how the legal minimum mesh size is designated, it is of im- 

 portance to have data available on the average amount and the range of the shrinkage 

 of pound-net and deep-trap-net twine following the application of a preservative. 



The results of 648 measurements of pound-net and deep-trap-net meshes as found 

 in use are recorded in table 47. 40 The data have been grouped according to the size 

 of the mesh (extension measure) as manufactured and to the type of preservative 

 applied. The former grouping (as to size of mesh when manufactured) is based en- 

 tirely on the fishermen's statements. The meshes were measured by inserting a thin 

 steel rule in one end of the collapsed mesh, pulling the twine taut, and reading the length 

 between and inside the knots (not from the centers of the knots). Measurements 

 were made both parallel with the selvage (first measurement of each series in table 47) 

 and at right angles to it (second measurement). 



Although most of the fishermen who were interviewed believed that tar shrinks 

 webbing more than does copper oleate. their belief is not entirely supported by the data 

 of table 47. It is true that tarred nets of 4 1 :'i-inch and 4 1 -.-inch original mesh size suf- 

 fered greater shrinkage than nets of the same mesh size treated with copper oleate. On 

 the other hand, nets with a factory measurement of 3 1 -j inches shrank considerably more 

 under copper-oleate treatment than did nets of the same mesh size treated with tar; 

 a slightly greater shrinkage from copper oleate was found also for 4-inch-mesh nets. If 

 all sizes of mesh are considered together, there appears to be little difference between the 



w Smith, Oliver H. and John Van Oosten. Tagging Experiments with Lake Trout, Whitefish, and Other Species of Fish from Lake Michigan. 

 Trans. Am. Fish. Soo., vol. 69, (1939) 1940, pp. 63-84. 



40 The data of table 47 do not represent 648 different nets as some nets were visited more than once. Several nets of mesh size larger than 4H 

 Inches as manufactured were measured, but there were not enough of any single mesh size to yield reliable averages. 



