330 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



78 percent in 1932 was followed by recoveries in 1933 and 1934 (89 and 106 percent, 

 respectively) and relatively high abundance in 1935 (91 percent). The decreases in 

 1935-1937 that led to the minimum of 45 in 1937 were followed by a recovery in 1938 

 and a slight decline in 1939. In both H-l and H-2 the secondary declines in abundance 

 were preceded by secondary increases in fishing intensity — increases traceable to revi- 

 vals of deep-trap-net operations. 



The remaining districts experienced greater ultimate declines than did H-l and 

 H-2. Furthermore, these districts failed to show recoveries comparable to those that 

 occurred in H-l and H-2. In H-3 the decline in abundance continued through 1935; 

 abundance remained rather stable at about 25 in the years, 1935-1938, and declined to 

 19 in 1939. The abundance in H-4 declined through 1934, was at approximately 50 

 percent in 1934-1937, and dropped to an extremely low level in 1938 and 1939. In both 

 H-5 and H-6 the decline in abundance that followed the introduction of the deep trap 

 net proceeded without interruption (albeit at an irregular rate) through 1939. In that 

 year whitefish were extremely scarce in both districts. 



The data that have been discussed in the preceding pages support the general con- 

 clusion that the deep trap net was in large measure responsible for a disastrous deple- 

 tion of the whitefish in the four southernmost districts of Lake Huron. This depletion 

 was the result of the unreasonable increases in fishing intensity and hence in production 

 in these districts. In the northern portion of the lake where the' net was used more 

 moderately the decline in the abundance of whitefish was severe but it did not reach 

 such extremes as were found in the central and southern regions of the lake. 



Largely for the sake of completeness the annual fluctuations of production, abun- 

 dance, and fishing intensity for all six districts combined have been presented graphically 

 in figure 11 (data from tables 5, 9, and 10 1. To some extent the data for the entire 



=1 Q 



19 3 3 

 CALENDAR 



19 3 5 

 YEAR 



Figure 11. — Annual fluctuations in the production (solid line) and abundance (long dashes) of whitefish and in the intensity of the whitefish fishery 

 (short dashes) in Lake Huron (all six districts combined). 1929-1939. 



lake lack significance as the combination of the data for all districts obscures the extreme 

 nature of the fluctuations that took place within the individual districts. The data 

 serve chiefly to show that a relatively great abundance of whitefish contributed ma- 

 terially to the high production in 1930-1932 (especially in 1930 and 1931), and that 

 the decline in catch subsequent to 1932 would have been much more rapid had not the 

 intensity of the fishery been so great. Although the decline in abundance began in 1932 

 the intensity of the fishery increased rapidly until 1933. Beyond 1932 the abundance 

 of whitefish was below the 11-year average and decreasing in every year. Fishing in- 

 tensity, however, did not return to the 11-year average before 1937 or to the 1929 level 

 before 1939. 



The question now arises, "What characteristics made the deep trap net so deadly 

 effective?" The tremendous production of deep trap nets was possible chiefly because: 

 (1) they can be set in deeper water, and hence in areas with greater concentrations of 

 whitefish, than can the pound nets; and (2) they are much more efficient in taking 

 whitefish than are gill nets fished on the same grounds. Attention will be given first 

 to the advantages of the deep trap net over the pound net. 



