WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 



345 



Table 21. — Annual fluctuations in the abundance percentages for whitefish in the various districts and areas 



of Lake Michigan, 1929-1939 



[Expressed as percentages of average 1929-1939 abundance. In the computation of percentages for areas of more than one district and for the 



entire late the abundance percentage for each district was weighted according to the percentage of the total 1929-1939 



production contributed by that district] 



A suggestion of overfishing is provided by the data for M-7. In this district the 

 greatest maximum yield (433 percent of the 1929-1939 average) was associated with 

 the lowest relative abundance (33 percent) in 1939 (table 18). Abundance in 1939 

 was low also in M-6 (53 percent), the district with the second highest maximum pro- 

 duction percentage (345). The maximum fishing intensity also was relatively high in 

 both M-6 and M-7 (242 and 271, respectively). On the other hand, the 1939 abun- 

 dance was low (41 percent) in M-5, where there was no indication of overfishing in 

 1929-1939 (maximum production, 183 percent of normal; maximum intensity, 129 

 percent of normal). 



Although, as stated previously, overfishing cannot be disregarded as a possible 

 contributing factor in the decline in abundance of the Lake Michigan whitefish, there 

 can be no doubt that overfishing was relatively unimportant in Lake Michigan as 

 compared with Lake Huron. In the discussion of the data for Lake Huron emphasis 

 was placed on the unreasonable expansion of fishing intensity and especially on the 

 fact that this intensity remained abnormally high even in the face of decreasing 

 abundance. The data for Lake Michigan, on the contrary, reveal a much more rational 

 relationship between abundance and fishing intensity (and hence between abundance 

 and yield). 



Despite certain exceptions it can be said that in the Lake Michigan districts, as a 

 whole, periods of relatively high abundance were also periods of relatively high fishing 

 intensity and production (tables 15, 19, and 21; figs. 13 to 20). It is true that the 

 changes in fishing intensity tended to lag somewhat behind the changes in abundance. 

 Commonly the peak of fishing intensity occurred a year or two later than the peak of 

 abundance, and the subsequent decline in fishing intensity was delayed correspondingly. 

 Nevertheless, fishing intensity and yield were above average in a large majority of the 

 years in which the abundance of whitefish was above average, and, conversely, fishing 

 intensity and production were below average in the majority of the years in which the 

 abundance of whitefish was below average. There was a tendency also for the per- 

 centages of fishing intensity and catch to be greater than the abundance percentages 

 when abundance was above average and less than the abundance percentages when 

 abundance was below average. The curves of fishing intensity tended to lie outside 

 (with reference to the average) the curves of abundance, and the curves of production 

 tended to fall outside both the curves of abundance and fishing .intensity. 



The tendency for the Lake Michigan fishermen to regulate their fishing activities 

 according to the abundance of whitefish is brought out further by the fact that the 

 coefficient of correlation between the percentages of fishing intensity and abundance 



