Fishery bulletin of the Fish and Wildlife Service - NOAA

WHITEFISH FISHERY OF LAKES HURON AND MICHIGAN 359
of two distinct concentration zones for both legal and undersized fish and in showing a
somewhat shallower habitat for ,the whitefish. The inshore concentrations, in both of
which the numbers of fish per lift exceeded those of the offshore concentrations, were 10
feet shallower than the maxima for the corresponding size groups in Lake Huron.
Consequently, the most suitable limit for the depth of water in which impounding nets
should be operated in Lake Michigan is 70 feet, 10 feet shallower than in Lake Huron.
BATHYMETRIC ÖISTRIBUTION OF OTHER SPECIES
Other species were much less numerous in the catches of pound nets and deep trap
nets than were whitefish. The data on the bathymétrie distribution of these "miscellaneous"
species, therefore, will not be given in the same detail as those on the distribution
of whitefish.
LAKE TROUT
Nearly all of the lake trout (Cristivomer namaycush) were of legal size (minimum
legal weight, 1% pounds). As undersized lake trout were so few and because there
was no evidence of important differences in the vertical distribution of legal and undersized
fish, tables 30, 31, and 32 have been prepared from the records of all trout taken,
regardless of size.
Lake Huron.—In the Alpena-Ossineke area (table 30) lake trout were numerous
in May (31.0 to 39.8 fish per lift) at depths greater than 100 feet, but only one trout
was taken in the lift from 81-90 feet. In June lake trout were fairly numerous in the
shallower water (41-70 feet) while the average catch per lift declined (in comparison
with the averages for May) in depths greater than 100 feet. The records for four lifts
from depths between 40 and 71 feet in July and August suggest that most lake trout
had abandoned the shallower water in these two months. Possibly this offshore movement
accounts for the increase over the catch for the month of June in the average
number of trout per lift from 81-120 feet. The average lifts in August were consistently
below those of July from depths of 71-120 feet, and the September catches were smaller
than those of August from the 101-120 foot interval. These decreases possibly may
represent a movement of the lake trout to depths greater than those in which .deep
trap nets were operated.
May
July
TABLE 30.—Number of lake trout per lift of pound nets and deep trap nets in the Alpena-
Ossineke area, 1931-1938
Month
41-80
Г 21.3
t (4)
í 0.0
1 (D
f 6.0
\ (2)
1 13.6
1 (7)
61-70
40.0
(D
1.0
(1)
20.5
(2)
[Number of lifts in parentheses^
Number of lake trout per lift at depth fin feet)
71-80
56.0
(D
7.9
(7)
13.9
(8)
81-90
Г 1.0
i (D
12.0
(1)
40.2
(5)
19.7
(9)
24.5
(16)
91-100
S.O
0)
35.5
(12)
25.5
(3)
31.9
(16)
101-110
31.0
(1)
16.9
(6)
26.2
(7)
22.4
(5)
/ 6.6
\ (5)
19.2
(24)
111-120
The seasons' averages indicate an irregular trend toward an increase in the abundance
of lake trout with increase in the depth gf the water. The decline in numbers in
depths of 101-110 feet may be real since similar decreases occurred in the catch for July
37.4
(23)
11.8
(18)
50.0
(23)
26.7
(Ш)
15.5
(2)
33.2
(76)
>120
39.8
(4) '
18.8
(5)
28.1
(9)