370 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



ination of the frequencies and averages indicates that probably few legal-sized trout 

 escaped through the meshes of 3Vo to 3 15/16 inches (about 4 to 4 7/16 inches as man- 

 ufactured) since the modal weight of the fish in these meshes (between 1^2 aQ d 1% 

 pounds) was the same as in the 3- to 3 7/16-inch meshes and the average weight of 

 legal-sized fish increased only 1.6 ounces in nets of the latter sizes of mesh. Individ- 

 uals of these sizes did escape through meshes larger than 3 15/16 inches. It is doubt- 

 ful, however, whether many fish of 1% pounds or larger were able to pass through 

 meshes of exactly 4 inches (about 4% inches as manufactured). 



It may be observed from the frequencies of weights that the bulk of the gilled 

 trout shifted to a higher weight-interval with each increase in the mesh between 3 and 

 4 7/16 inches, but the fish were always concentrated within a relatively small range of 

 weight (% to 1 pound). The majority of the gilled trout weighed between l a /4 and 2 

 pounds in the 3- to 3 7/16-inch mesh, between IV 2 and 2V 2 pounds in the 3 ] /2- to 3 15/16- 

 inch mesh, and between 1% and 2Y 2 pounds in the 4- to 4 7/16-inch mesh. The ranges 

 in length of the bulk of the trout (table 42) varied from about 1 to 2y 2 inches in these 

 various meshes (18 - 19%; 17 1 - - 20; 20-21 inches). 



The average weight of the undersized gilled trout, as well as the average length 

 (table 42), increased with an increase in the size of mesh from less than 3 inches to 

 3 to 3 7/16 inches (indicating release of some small fish). The size of fish did not 

 change, however (slight increase in weight; slight decrease in length), with a further 

 increase of y 2 inch in mesh size suggesting that, though additional undersized fish were 

 released by the larger meshes, the size of mesh was not yet sufficiently large to permit 

 the larger undersized trout to escape. An increase of another y% inch in the size of the 

 mesh apparently did permit this escapement for no undersized trout were gilled in 

 meshes of 4 to 4 7/16 inches. Even though these meshes or larger ones are used, it 

 may not be assumed that no undersized fish would remain in the net. They do not 

 all attempt to escape. 



The average weight and length of the legal-sized gilled trout increased slightly 

 with an increase in mesh size from 3 to 3 7/16 to Z x / 2 to 3 15/16 inches (indicating re- 

 lease of only a few fish), but increased to a greater degree with a further %-inch 

 increase of mesh size, suggesting that some of the smaller fish of legal size had es- 

 caped. Nearly all of the trout gilled in meshes of 4 to 4 7/16 inches weighed 1 3 A 

 pounds or more. 



In general, the data on the gilled fish and on the average sizes of fish retained 

 in the impounding nets indicate that Michigan's minimum size of mesh (4V:> inches as 

 found in use) prescribed for the pots of impounding nets employed in catching whitefish 

 and lake trout should not be reduced. This mesh is in fact too small to liberate a large 

 proportion of the undersized whitefish found in the nets, although on the other hand it is 

 too large to hold the smaller individuals of the legal-sized trout. A 4-inch mesh as 

 found in use would probably prove more effective for the capture of trout at the present 

 size limit of 1H pounds. A better solution than a reduction in mesh to prevent the 

 escape of legal-sized trout would be a substantial increase in the legal size limit since 

 most lake trout (especially the females) under 3 pounds are sexually immature. It is 

 not practicable to prescribe different meshes for whitefish and trout as both species are 

 usually taken together on the same grounds. Further, a 4* o-inch mesh is also prescribed 

 for gill nets employed for both species. | ;t j, 



DESTRUCTION OF WHITEFISH THROUGH GILLING IN THE MESHES 

 OF POUND NETS AND DEEP TRAP NETS 



The gilling of undersized fish in the meshes of impounding nets constitutes a cer- 

 tain source of destruction since death follows soon after the individual is enmeshed. 

 It is, therefore, of importance to know what percentage of the illegal-sized whitefish 

 become gilled in commercial pound nets and deep trap nets, and how this percentage 

 varies with the size of the mesh. The death of legal individuals through gilling is of 

 lesser importance, although the market value of such fish may be impaired and large 

 numbers of gilled fish of any size add considerably to the fishermen's labor in clear- 

 ing their nets. 



