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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



each mesh size when the commercial yields are equal. This determination (third row 

 in body of table) shows that large-mesh nets that take an average of 81.8 legal fish 

 may be expected to contain an average of 57.6 illegal individuals as compared with 

 77.7 undersized whitefish in small-mesh nets with equal commercial lifts. 



From the averages of 77.7 and 57.6 illegal whitefish per lift it may be estimated 



that large-mesh nets released 100 X 



77.7 



57.6 



77.7 



or 25.9 percent of the undersized 



individuals. For every 100 illegal whitefish taken in small-mesh nets, 74.1 should 

 be taken by large-mesh nets with the same commercial catch. 



The data of table 36 and the computations based upon them are open to the very 

 serious objection that the actual numbers and the percentages of legal and illegal fish 

 taken in nets of any size of mesh vary according to the nature of the stock at the place 

 and time the nets are fished. Truly discriminating data on selectivity must be founded 

 on the lifts of nets that are identical except for the size of mesh and that are fished 

 under strictly comparable conditions, that is, on the same grounds, at the same depth, 

 in the same year, and at the same time within the season. 



Table 37 contains comparisons of the catch of large-mesh and small-mesh pound 

 nets and deep trap nets, based on lifts made- in the same year (1932), in the same 

 month, on the same grounds, and at the same depth. The data are confined to com- 

 parisons in which nets of both sizes of mesh are represented by at least 5 lifts. The 

 necessary restrictions reduced the number of possible comparisons. However, the 

 averages of the 10 independent sets of observations are reasonably reliable. 



Table 37. — Comparison of the numbers of legal and illegal whitefish per lift in small-mesh and large-mesh 

 pound nets and deep trap nets fished in the same year (1932) and month, on the same grounds, and at 

 comparable depths 



[Number of lifts in parentheses] 



The averages of the 10 comparisons show that the large-mesh pound nets and 

 deep trap nets took more legal whitefish and fewer illegal fish than the small-mesh 

 nets fished under comparable conditions. In round numbers, small-mesh nets took an 

 average of 92 undersized individuals in producing 74 fish of marketable size, whereas 

 large-mesh nets took only 78 illegal whitefish for a commercial production of 92 fish. 

 The correction for equal commercial production shows that small-mesh pound nets 

 and deep trap nets with a commercial catch equal to that of large-mesh nets (92 fish) 



