FISHERIES EST MICHIGAN WATERS OF GREEN BAT 



15 



200 



00 



UJ 



< 



H 



Z 

 UJ 



O 

 rr 

 in 

 n. 



1930 



1935 



1940 



1945 



Figure 15. — All species: Commercial production in State of Michigan waters of Green Bay, 1929-49, in millions of 



pounds and as percentages of the 1929-43 mean. 



trout — 87,000 pounds), and except for the stur- 

 geon 5 did not exceed 40.8 percent (the figure for 

 the lake trout). 



Table 6. — Comparison of production in the commercial 

 fisheries of Oreen Bay, by species, 1891-1908 and 

 1929-49 



' All suckers in 1891-1908; white and redhorse suckers in 1929-^9. 

 » See tables 2 and 4 for list of species included. 



The changes from 1891-1908 to 1929-^9 in total 

 production, in the take of the individual species, 

 and in the species composition of the catch offer 

 wide fields for speculation but the theories that can 

 be advanced in explanation of these changes are 



• The taking of sturgeon became illegal In 1929. 

 227160—53 3 



mostly without supporting evidence. The shifts 

 in production — increases of yield for some species 

 and decreases for others — give prima facie evi- 

 dence of changes in the conditions affecting the 

 population as a whole, but we have little knowledge 

 of the mechanisms whereby these changes came 

 about. Fishing surely played an important role ; 

 however, it must have placed different degrees of 

 pressure on different species and in turn the several 

 species must have exhibited varying degrees of 

 resistance to fishing pressure. Similarly, the ef- 

 fects of physical-chemical changes brought about 

 by sawdust, bark, and other debris from the earlier 

 lumbering period, by the varied industrial waste 

 of the present era, by the fertilizing action of 

 domestic sewage and of drainage from agricultural 

 lands must have been significant and must have 

 varied with the species of fish. 



The differences from species to species in the 

 direction of change in production from 1891-1908 

 to 1929-49 make any attempt to appraise the effects 

 of fishing on the stocks especially difficult. Sta- 

 tistics on lake herring and whitefish illustrate the 

 nature of the problem. It is inviting, for example, 

 to explain the enormous drop in the production of 

 lake herring from nearly 6 million pounds to barely 

 1 million pounds as depletion resulting from over- 

 exploitation. If this explanation is accepted, how- 

 ever, we are confronted at once with the problem 



