WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 



327 



In the previous section attention was called to the existence of a typical deep- 

 trap-net cycle of production (p. 319) in which the catch "was raised to tremendous 

 heights for about 2 years, only to fall away sharply." It is equally valid to speak 

 of "typical deep-trap-net cycles" of fishing intensity and in the abundance of white- 

 fish. (For graphical representations of the annual fluctuations in the catch and 

 abundance of whitefish and in the intensity of the whitefish fishery in the several 

 districts, see figs. 5 to 10.) The tremendous increases in yields were accompanied by 



I 9 J 3 I S 3 S 



CALENDAR YEAR 



Figi're 1U. — Sixth district, H-6. 



great increases in fishing intensity (table 8). To a large extent these increases in 

 intensity represented deep-trap-net operations (table 9). In about 2 years, however, 

 the fishing intensity declined in a district as the fishermen moved on to more produc- 

 tive grounds. An exception to this cycle of intensity is to be found in H-6 where an 

 extremely intensive fishery was carried on for 5 years (1934-1938) despite a rapid 

 decrease in the returns. Operators of deep trap nets remained longer in H-6 because 

 the more northerly grounds had been exploited thoroughly in previous years (p. 321). 

 H-l and H-2 showed limited secondary increases in fishing intensity (about 1935-1937 

 in H-l and 1934-1935 in H-2) as some fishermen returned from the depleted grounds 

 in the south. 



Without exception the abundance of whitefish fell sharply after a period (usually 

 2 years) of intensive deep-trap-net operations. This fact is brought out clearly by the 

 data of table 10 in which the years of greatest production of deep trap nets have 

 been designated. (The comparison of tables 4 and 9 will reveal that the years of 

 greatest yields of deep trap nets and the years of greatest intensity of the deep-trap-net 

 fishery were not always the same.) The nature of the changes in abundance that fol- 

 lowed heavy removals of whitefish may be summarized for the districts as follows: 



H-l. Abundance began to decline in 1931, the second year of heavy production 

 by deep trap nets. This decline continued through 1933. 



Table 8. — Annual fluctuations in the intensity of the fishery for whitefish in each district of Lake Huron 

 [Expressed as percentages of the average 1929-1939 intensity in the district) 



