mesh was changed to 2-1/2 inches, flexible- 

 rule measure. 9/ This last change had little 

 actual effect on the legal mesh size since a 

 2-1/2 inch mesh, flexible-rule measure, is 

 roughly equivalent to 2-5/8 inch mesh, stretched 

 measure. The 2-1/2 inch mesh continued to be 

 the legal minimum in Michigan through 1953 . 



In Illinois, where records of catch-per- 

 unit-effort start with 1950, the minimum legal 

 mesh size for chubs was 2-3/8 inches, flexible 

 rule, in 1950 through June 30, 1951; after June 

 30, 1951, it was 2-1/4 inches. The minimum 

 mesh size in Wisconsin was 2-1/2 inches, flex- 

 ible rule, in 1953, the one year for which we 

 have these records . There are no records of 

 catch -per-unit-effort for Indiana. 



The extent of variability in the enforce- 

 ment of the law and the effects of lax enforcement 

 on records of catch -per -unit -effort are difficult 

 to determine . It is well known that over extended 

 periods little enforcement was attempted. Con- 

 cerning this matter Van Oosten has written as 

 follows: 10/ 



"As a matter of fact, for many years 

 none of the four states fronting Lake Michigan 

 enforced its law on the mesh of chub nets . Be- 

 cause of this lack of enforcement the mesh in 

 actual use became smaller and smaller until 

 many nets had meshes as small as 2-1/4 and 

 2-1/8 inches, stretched measure . Michigan 

 fishermen, however, seldom if ever employed 

 meshes smaller than 2-1/2 inches. It is safe 

 to say that for many years not a legal mesh net 

 was actually employed for chubs in the Lake 

 Michigan waters of Wisconsin, Illinois and 

 Indiana." 



0/ A thin steel rule of a length equal to the mini- 

 mum mesh size is bent slightly, inserted in the 

 mesh, and released; if it straightens within 2 

 seconds without slipping the knot or breaking 

 the twine, the mesh is legal. Inasmuch as the 

 rules are so constructed that they exert pres- 

 sure of approximately 1 pound when bent so 

 that the center is deflected 1/10 of the length, 

 this method of gaging is objective and influenced 

 only moderately by the flexibility of the twine . 



Dr. Van Oosten also has advised us per- 

 sonally that in the early 1930' s Michigan officials 

 were deliberately lenient in the enforcement of 

 the chub-net law pending issuance of recommenda- 

 tions on mesh size resulting from the experiment- 

 al fishing of the Fulmar . (Actually, the recom- 

 mendation of 2-3/4 inch mesh was ignored by all 

 four states.) It seems possible, therefore, that 

 the change of minimum mesh size from 2-3/4 to 

 2-5/8 inches in 1933 had little effect on the gear 

 fished by State of Michigan fishermen; it may 

 only have made legal the equipment long in use. 

 Since enforcement of the mesh law in Michigan 

 has been reasonably efficient the last 20 years 

 or longer and since the shift in 1939 from 2-5/8 

 inch mesh, stretched measure, to 2-1/2 inch 

 mesh, flexible rule, entailed little real change, 

 it appears that the effects of changes in the law 

 on records of catch-per-unit-effort were smaller 

 than might be suspected- -indeed, may have been 

 of limited consequence . 



There is reason to believe that in 1953 

 most nets fished in Wisconsin had legal-sized 

 meshes. We do not know of changes in enforce- 

 ment policies in Illinois in 1950-1953. 



Two changes in the twine in chub gill nets 

 have biased our records of catch -per -unit of 

 effort. First was the substitution of "Sea Island" 

 cotton, a highly flexible twine, for the traditional 

 linen webbing. According to Van Oosten (see 

 footnote 10) this changeover started in Wisconsin 

 in 1929. These "rubber nets" had two significant 

 characteristics: first, they were good fish- 

 catchers and second, the extreme flexibility of 

 the twine made laws on minimum mesh size 

 largely ineffective under the stretched-measure 

 system of gaging. (This second "advantage" 

 was much reduced by the introduction of the 

 flexible rule.) Once the cotton nets were intro- 

 duced their use spread rapidly and soon became 

 general throughout the lake . 



10/ "Brief resume of the history of the changes 

 in the size of mesh employed in chub nets in Lake 

 Michigan, particularly in Wisconsin waters, " by 

 John Van Oosten; this memorandum was prepared 

 in 1941 and was mimeographed by the Wisconsin 

 Conservation Department in 1947. 



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