16 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



of accounting for the simultaneous increase (from 

 159,000 pounds to 714,000 pounds) in the average 

 annual take of whitefish — a species much higher 

 priced than the lake herring, always in market 

 demand, and continually subject to intensive 

 fishing. 



Seemingly paradoxical situations such as the 

 one just described become less perplexing if we 

 admit the concept that in mixed stocks of the type 

 found in Green Bay and other shallow-water 

 areas of the Great Lakes (that is, stocks in which 

 several species not closely related and of different 

 habits are present in number) the effects of fishing 

 should be considered in terms of the entire popu- 

 lation rather than individual species, and recog- 

 nize that a major effect of fishing lies in the dis- 

 turbance of ecological relations among the fishes. 

 Thus, fishing pressure to which the species are 

 subject in common may give one a competitive 

 advantage and place another at a disadvantage. 

 Differences of fecundity, growth, and longevity, 

 . . . that lead to a particular species composition 

 at one level of fishing intensity may bring about a 

 greatly different composition at another. Changes 

 of this origin can be accentuated if fishing pres- 

 sures, relative to the actual stock, differ from spe- 

 cies to species. Furthermore, the generally lower 

 level of commercial production in the modern pe- 

 riod suggests the possibility that fishing pressure 

 on commercially exploited species may have oper- 

 ated so much to the advantage of the smaller, non- 

 commercial species that the latter now make up 

 an increased percentage of the total biological 

 production. 



SEASONAL TRENDS OF PRODUCTION 



AND COMPOSITION OF THE CATCH 



ACCORDING TO GEAR 



The statistics on seasonal trends of production 

 (tables 7 and 8) and on the gear composition of 

 the catch (table 9) of the principal species in State 

 of Michigan waters of Green Bay were based on 

 the records for 1929^19. The presentation of 

 these data for the 1929-43 base period would be 

 little to the point since we are concerned here with 

 average conditions and not with trends of annual 

 fluctuation about a norm. Seasonal trends and 

 gear composition both varied considerably from 

 year to year, but the expansion of the tabular ma- 

 terial to show these variations is not justified. 



SEASONAL DISTRIBUTION OF THE CATCH 



The data on monthly and quarterly trends of 

 production for five of the seven species listed in 

 tables 7 and 8 were affected materially by closed 

 seasons. These seasons as presently defined by 



Table 7. — Percentage distribution, by month and quarter, 

 of the average annual catch of the principal species of 

 fish in Green Bay, 1929-49 



Table 8. — Distribution, by month and quarter, of the 

 average catch of the principal species of fish in Green 

 Bay, 1929-1,9 



[In thousands of pounds] 



Michigan State law 6 are as follows (seasons open 

 and close at noon on the dates indicated) : Lake 

 trout, October 10-November 10 ; whitefish, Novem- 

 ber 5-December 10; walleye, April 1-May 20; 



Some adjustments have been made in the closed seasons since 

 1928, but a detailed account of these changes does not seem 

 desirable. 



