342 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



the four consecutive years, 1929-1932 (table 15), may well have contributed to the 

 sharp decline in abundance in 1933 (table 21). Similarly, in other districts the declines 

 in abundance that followed years of increased fishing intensity and high yields might 

 have been less severe had the fishery of the preceding years been less intensive. The 

 actual detection of the possible effects of high production on the abundance of white- 

 fish in later years is difficult, since in Lake Michigan as in Lake Huron a decline from 

 the peak of abnormal abundance was to be anticipated whether or not extensive over- 

 fishing occurred. Furthermore, the data for Lake Michigan do not provide the sharp 

 contrasts that made the presence and effects of overfishing in Lake Huron so easy to 

 detect. (Compare especially the annual fluctuations in the production and fishing 

 intensity in the various districts of the two lakes — figs. 5-10 for Lake Huron and 

 13-20 for Lake Michigan.) 





f 9 3 3 19 3 5 



CALENDAR YEAR 



Figure 14. — Second district, M-2. 



- ISO 



I 



- 2 5 



2 < Q 



19 3 3 

 CALENDAR 



I 9 3 5 

 YEAR 



Figure 15.— Third district, M-3. 



19 3 3 19 3 5 



CALENDAR YEAR 



Figire 16— Fourth district, M-4. 



