Fishery bulletin of the Fish and Wildlife Service - NOAA

372 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
of bloated fish (legal and illegal fish combined) in the lift rose consistently as the depth
of water increased. No fish were bloated in nets (mostly pound nets) set at depths of
60 feet and less. At depths of 61-80 and 81-100 feet slightly less than one-half of
one percent were bloated. The percentage of bloated whitefish increased to 1.08 in 101-
110 feet, and rose still further to 1.70 percent in deep water (more than 110 feet).
The data on the percentages of the legal and of the illegal whitefish that were
bloated reveal that both sizes of fish share the general trend toward increased bloating
with increase in the depth of the water. The greater percentage of bloated legal fish at
61-80 feet in comparison with the percentage at 81-100 feet constitutes the only
exception. At all depths beyond 80 feet relatively more of the illegal whitefish than
of the legal whitefish were bloated. This difference was probably due to the thinner
body wall of the younger fish. The averages for fish taken at all depths show that
0.63 percent of all legal fish and 1.17 percent of all illegal fish were bloated.
The bloating of live whitefish was probably an unimportant source of destruction
of undersized individuals. Only 1.17 percent of all illegal fish were bloated and the
maximum percentage of bloated fish at any one depth was 2.08 (deep water). However,
the repeated capture of undersized fish, would increase the risk of injury or death
through bloating.
DEAD WHITEFISH IN POUND NETS AND DEEP TRAP NETS
Commercial fishermen opposed to the use of deep trap nets contended that confinement
in this type of gear was fatal to whitefish and that dead illegal fish were very
numerous in the lifts. The data of table 45, which show the number and percentage of
dead fish (exclusive of dead gilled fish) at three different depths and the percentages of
the legal and of the illegal fish found dead at these same depths, do not, in general, support
this contention.
TABLE 45.—Relationship between the depth of the water and the numbers and percentages of dead whuefiah
in deep trap nets in Lakes Huron and .Michigan, 1931-1932 data combined for all localities in
each lake
Michigan
1
1
Lake
Depth of water
(feet;
(110 . .
All depths
(110
All depths
Total number of
fiah'
4,734
35736
30,313
70783
11,613
36215
• 827
48655
Includes only lifts in which dead fish were counted.
Only 72 percent of the dead fish were separated as to sue.
Number of dead
fuh
107
209
195
511
24
69 2
95
Percentage dead
Esh
2 26
0 58
0 64
0 72
0 21
0 19
0 24
0 20
Percentage dead
legal fish:
0.44
0 32
0 45
0.38
0.05
0 08
0 26
0 08
Percentage dead
illegal fish>
Almost 4 percent of the undersized whitefish were dead in the Lake Huron deep trap
nets lifted from depths of 80 feet or less. However, at that time (1931-1932)
relatively few deep trap nets were fished in such shallow water. Less than 1 percent
of the illegal whitefish were dead in nets lifted from greater depths. The average percentage
of the undersized fish found dead in the lifts of all deep trap nets observed
in Lake Huron was slightly above 1 percent. The percentage of the dead among the
legal whitefish in Lake Huron deep trap nets was small (average, 0.38 percent) and
showed little variation with the depth of the water.
The percentages of both the legal and the illegal whitefish found dead in deep trap
. nets were much smaller in Lake Michigan than in Lake Huron. The shallow-water lifts
(80 feet and less) in particular had relatively few dead fish as compared with nets
from the same depth in Lake Huron. The percentages of dead whitefish in Lake
3 96
0 90
0 84
1 10
0 35
0 35
0 22
0 35