PART IV 



OBSERVATIONS ON THE FISHING ACTION OF POUND NETS 

 AND DEEP TRAP NETS 



EFFECT OF THE SIZE OF THE MESH ON THE CATCH OF LEGAL- 

 AND ILLEGAL-SIZED WHITEFISH AND LAKE TROUT 



The question of the proper legal minimum size of mesh is a highly controversial 

 one that involves nearly all commercial fishing gears. Certainly the most desirable 

 size of mesh is that which releases the greatest number of illegal-sized and immature 

 fish without serious loss of legal-sized fish. However, a great diversity of opinion 

 exists as to what this "desirable" size of mesh may be. Although there are a few excep- 

 tions, commercial fishermen usually oppose most vigorously any attempt to increase 

 the legal minimum mesh size, and in practice generally fish the smallest mesh per- 

 mitted by law. 



The lack of proper legal regulations and enforcement in the early years of the 

 deep-trap-net fishery led to a wide range of mesh size in this gear. Many of the 

 early deep trap nets had meshes that were ridiculously small (as small as 2 1 /± inches, 

 stretched measure as fished) for a gear designed to take a species with a 2-pound 

 legal-size limit. Continued experience, however, led many deep-trap-net fishermen to 

 increase the size of mesh in their nets. This increase in mesh size not only reduced 

 the labor of sorting out the illegal fish and returning them to the lake, but also im- 

 proved the catch of legal fish as will now be shown. 



The data in tables 36 and 37 on mesh selectivity in pound nets and deep trap nets 

 are based on comparison of the numbers of legal- and illegal-sized whitefish (2-pound 

 size limit) taken in nets with meshes less than 4 inches (stretched measure as fished) 

 and in nets with meshes of 4 inches and more. For convenience in the discussion, the 

 two groups of nets will be termed "small-mesh" and "large-mesh" nets. 36 



Table 36 lists the total numbers of legal and illegal fish, the average numbers per 

 lift, and the percentages of fish of both size groups in all lifts of large-mesh and small- 

 mesh pound nets and deep trap nets observed in the course of the investigation. On 

 the average, small-mesh nets took more fish per lift, both legal and illegal, than did 

 large-mesh nets. The percentage of legal fish in the lift was higher (58.7 as compared 

 with 51.3) in large-mesh nets. 



Table 36. — Comparison of total numbers, averages per lift, and percentages of legal and illegal whitefish 

 taken in small-mesh and large-mesh pound nets and deep trap nets 



[The 1931-1932 data have be<>n combined for all ports, all depths, and all months. Numbers of lifts in parentheses] 



Item 



Whitefish taken in mesh 



Less than 4 inches 



Legal 



Illegal 



4 inches and more 



Legal 



Illegal 



Total number of whitefish taken 



Average number of whitefish per lift . 

 Corrected for equal commercial yields 

 Percentage legal and illegal 



48.939 



81.8 

 81 8 

 51 3 



(598) 



77.7 

 77.7 

 48 7 



76 6 

 31 8 

 58 7 



(238) 



12,820 



53 9 

 57 6 

 41 3 



The unequal numbers of fish in the lifts of large-mesh and small-mesh nets make 

 a comparison of their selective action difficult. A better comparison is made possible 

 by the determination of the numbers of illegal fish that must be handled in nets of 



« In the original compilations the nets were grouped according to m?sh size by half-inch intervals. This grouping proved unsatisfactory, how- 

 ever, since nets that fell within som? intervals of m'sh s'z> were fished chieflv on grounds with an abundance of undersized whitefish whereas the 

 nets of other mesh sizes were fished predominantly on grounds where young whitefish were extremely scarce. In order to reduce irregularities from 

 this source, only two size groups of mesh were employed in the preparation of data on the release of illegal-sized whitefish. 



365 



