Fishery bulletin of the Fish and Wildlife Service - NOAA

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 whiteflsh 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 bathymétrie distribution
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 information.
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 bathymétrie 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