358 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



young fish from capture and excessive handling, and of reducing production 35 to a level 

 which does not threaten the extermination of the commercial stock?" 



Ordinarily fishery legislation must be framed in conformity with average condi- 

 tions during the entire season over a large part of a lake or an entire lake. Consequently, 

 the most suitable data on the bathymetric distribution of whitefish in Lakes Huron and 

 Michigan, as they pertain to fishery regulation, are those obtained by combining the 

 available material for all grounds and all times in the fishing season in each of the 

 two lakes. The data of table 29 (see also fig. 23) represent such combinations. 



Table 29. — Number of legal and illegal whitefish per lift of pound nets and deep trap nets in Lakes Huron 



and Michigan, 1931-1932 

 [Number of lifts in parentheses. Asterisks indicate concentrations] 



It should be pointed out, however, that recommendations based on the averages of 

 table 29 which cover general conditions likewise cover very well the local conditions on 

 the different grounds in the lake despite the variations in the bathymetric distribution of 

 the legal and illegal whitefish in different localities. 



In Lake Huron the average number of legal whitefish per lift increased continu- 

 ously with increase in the depth of the water up to a maximum at 91-100 feet, 

 decreased in the next two intervals, and increased slightly at more than 120 feet. The 

 increase in the deepest water can be traced to the small number of lifts from this depth 

 off Alpena, a region in which legal-sized whitefish were scarce. The limits of the general 

 region of greatest abundance of legal fish may be set at approximately 81-110 feet. The 

 number of undersized whitefish increased also from shallow to deeper water, but the 

 maximum occurred at 81-90 feet, or 10 feet shallower than the depth of maximum 

 abundance of legal fish. A second but lower peak in the number of illegal whitefish 

 per lift was found at 101-110 feet. If legal fish are to be protected from excessive 

 exploitation and illegal fish from frequent handling, the obvious depth limit beyond 

 which impounding nets should not be fished in Lake Huron is 80 feet. Although this 

 restriction curtails the production of deep trap nets severely, it cannot be considered 

 extreme or oppressive, since a closely similar gear, the pound net, long supported a 

 productive and prosperous fishery in even shallower water. (Few pound nets are fished 

 in depths of more than 65 or 70 feet.) 



The restriction of impounding nets in Lake Huron to depths of 80 feet or less does 

 not mean the complete closure of the deeper waters to the commercial fishery for white- 

 fish. These deeper areas are still open to the gill net, which was formerly the only gear 

 fished in them. However, past experience has demonstrated that in these areas gill nets 

 ordinarily did not catch whitefish in quantities dangerous to the stability of the stock. 

 Furthermore, the selective action of the gill nets commonly employed precludes the 

 capture of excessive numbers of small fish and also spares the large individuals that 

 constitute the spawning reserve. 



The Lake Michigan data differ from those of Lake Huron chiefly in the presence 



11 The present policy of fishery regulation in the State of Michigan waters of the Great Lakes does not include control of production through the 

 limitation of the amount of gear fished or the setting of arbitrary limits on the season's catch. 



