332 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 12. — Monthly production of whitefish in Lake Huron, 1929 and 1931, in gill nets, deep trap nets, 



pound nets, and all gears combined 



[Percentages are in parentheses] 



only during limited periods, one in late spring and early summer and another in mid- 

 autumn. Many fishermen discontinue pound-net operations at other seasons. It is 

 true also that even in periods of active operation the greatest concentrations of whitefish 

 may be at depths beyond the reach of pound nets. 



The offshore movement that leads to a concentration in relatively deep water in 

 the summer and early autumn exposes the whitefish to the inroads of the deep trap net 

 at the time it is most vulnerable. Formerly, the only toll on the whitefish in its summer 

 concentration was that levied by gill nets, and in the modern fishery of Lake Huron this 

 type of gear has not proved generally effective for the large-scale catching of whitefish. 

 The gill net is so ineffective for the capture of whitefish under modern conditions that 

 gill-net fisheries are supported by this species alone only in very limited areas or over 

 extremely short periods of time (chiefly during the spawning season). 26 The large- 

 mesh gill-net fishery is now conducted ordinarily for the capture of both trout and 

 whitefish or of trout alone, but very seldom exclusively for the taking of whitefish. 27 

 The comparative ineffectiveness of gill nets made the time of summer concentration of 

 the whitefish a "semi-closed" season during which the species was in large measure 

 immune to capture. The introduction of the deep trap net made this same period the 

 season of maximum production. 



The effect of the deep-trap-net fishery on the monthly distribution of the whitefish 

 catch and the high production this gear made possible in the summer months may be 

 illustrated by the data of table 12 and figure 12. The gill-net season extended through 

 the months, May-August, in both 1929 and 1931. (September was a fairly good month 

 in 1929.) No distinct peaks occurred in either year. The pound-net catch, on the 

 contrary, was divided into two distinct seasons, each with a sharp peak. The early- 

 season maximum occurred in July in 1929 and in June in 1931. Both of the autumn 

 maxima were in October. The 1931 data' which show the more pronounced summer 

 depression provide the better description of the monthly distribution of pound-net pro- 

 duction because the 1929 early-summer peak was later and the September catch was 

 relatively higher than usual. The data for both years, however, have a distinct late- 

 summer minimum — August in 1929 and August-September in 1931. 



The curve of total catch in 1929 has a minimum in August corresponding to the 

 August depression in the pound-net data. A similar minimum would have existed in 



M When gill nets were fished on the spawning grounds the catches were sometimes enormous — thousands of pounds in a single lift. 

 JT This statement holds true even in Lake Michigan where the gill net is normally the dominant gear for the production of whitefish. 



