PART III 



BATHYMETRIC DISTRIBUTION OF WHITEFISH AND OF CERTAIN 



OTHER SPECIES IN THE SHALLOWER WATERS OF 



LAKES HURON AND MICHIGAN 



The following sections are based on counts of whitefish and certain other species 

 in 456 lifts of pound nets and deep trap nets in Lake Huron and 380 lifts in Lake 

 Michigan in the years, 1931-1932. The original compilations of the data were much 

 more detailed than those presented here. The tables showing the bathymetric distri- 

 bution of the fish represent combinations of large-mesh (4 inches and larger, stretched 

 measure) and small-mesh (less than 4 inches) nets of different dimensions, of different 

 fishing grounds in the same general area, and of data for corresponding months in 1931 

 and 1932. However, these combinations were made only after a careful examination 

 of the material demonstrated that the condensed data did not lead to conclusions that 

 were at variance with those that would have been drawn from more detailed infor- 

 mation. 



In the main, the data have been compiled according to 10-foot depth intervals. 

 However, for species other than the yellow pike, all lifts of nets from depths of 40 feet 

 and less have been combined, as have also those from 41-60 feet. In deep water 

 all lifts from more than 120 feet (more than 110 feet in Lake Michigan) have been 

 combined. The greatest depth in which a deep trap net was set, so far as we know, 

 was about 160 feet. This net was set in Lake Huron. Seldom were deep trap nets 

 placed in water deeper than 140 feet. In Lake Michigan the whitefish grounds were 

 located in much shallower water. Although a few pound nets set in more than 60 feet 

 of water were visited and a few deep-trap-net lifts from depths of 60 feet or less were 

 observed, for practical purposes the 60-foot contour may be considered as the line of 

 separation of the two types of gear. The change from pound nets to deep trap nets at 

 a depth of about 60 feet should not affect the value of the data, since we did not find 

 any important differences in the catch of pound nets and deep trap nets that were 

 fished in the same depth of water. All lifts observed from depths of more than 120 

 feet were made in Lake Huron. 



As a convenience in reading the tables, asterisks have been employed to designate 

 those depth intervals that contained the more significant peak concentrations of fish. 

 As an additional convenience, whitefish and yellow pike frequently will be termed 

 merely "legal" and "illegal" fish on the basis of a 2-pound and l^-pound size limit, 

 respectively, which limits were in effect in Michigan at the time of the investigation. 



BATHYMETRIC DISTRIBUTION OF WHITEFISH IN LAKE HURON 



NORTHERN LAKE HURON (CHEBOYGAN AND ROGERS CITY) 



The number of lifts (20) of pound nets and deep trap nets observed in northern 

 Lake Huron was insufficient to provide reliable data on the bathymetric distribution of 

 the whitefish. The largest lifts of legal-sized whitefish were taken from depths of 71-80 

 feet in July and August and of 61-70 feet in September (table 23). The greatest 

 numbers of illegal-sized fish occurred in lifts from 71-80 and 91-100 feet. (Only 

 one lift from the latter depth was observed.) 



ALPENA- OSSINEKE GROUNDS 



Although a fairly large number (158) of pound-net and deep-trap-net lifts was 

 examined on the Alpena and Ossineke grounds, the scarcity of data for the shallower 

 water makes a detailed description of the depth distribution of whitefish in this area 

 impossible (table 24). Nearly half of the lifts were from depths of 111-120 feet and the 



348 



