Fishery bulletin of the Fish and Wildlife Service - NOAA

378 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
255,000 pounds was less than half the previously reported all-time low (555,000 pounds
in 1900).
c. The statistics of the whitefish fishery of northern Lake Michigan (districts M-l,
M-2, and M-3) for the years, 1929-1939, lend support to the conclusions based on the
data for Lake Huron. In these Lake Michigan districts as in H-1 and H-2 the development
of the deep-trap-net fishery may be termed relatively moderate. Although the
whitefish fishery of northern Lake Michigan underwent a decline—a decline to which
the use of deep trap nets may have contributed substantially—the seVerity of the
decreases did not approach that of the decreases of central and southern Lake Huron;
rather the changes resembled those that took place in northern Lake Huron. The deep
trap net was of no significance in the State of Michigan waters south of district M-3,
except in M-7 where it was the dominant gear for the production of whitefish in the
single year, 1934.
6. The harmful effects of the deep-trap-net fishery can be traced to its great efficiency
for the capture of whitefish in comparison with'pound nets and large-mesh gill
nets. Pound nets, which are held in position by stakes driven into the bottom of the
lake, occupy the same position throughout the season, can be set only on soft bottom,
and seldom are fished in water deeper than 60 feet. Deep trap nets, which are held
• in position by anchors and buoys, can be set on almost any kind of bottom and can be
moved readily to any depth of water in which whitefish occur abundantly. These
characteristics of the gear made possible the heavy exploitation of the whitefish at the
time of their summer concentration in relatively deep water—far beyond the reach of
pound nets. Gill nets have long been fished in these depths of the summer concentration
of whitefish but in the modern fishery this gear has proved to be relatively unsuccessful
for the capture of whitefish, except under certain special conditions (as during
the spawning run or in limited local areas).
7. Records of the catch per lift of deep trap nets revealed that the gear was much
less successful in northern Lake Huron (districts H-1 and H-2) and Lake Michigan
(districts M-l, M-2, M-3, and M-7) than in central and southern Lake Huron (H-3 to
H-6). This situation doubtless accounted in part (see p. 339) for the relatively less
extensive development of the deep-trap-net fishery in Lake Michigan and northern
Lake Huron.
8. Counts of legal- and illegal-sized whitefish in lifts of pound nets and deep trap
nets from different depths of water were employed in a study of the bathymétrie distribution
and vertical movements of the species during the summer and early autumn.
9. The combined data for the months, May to October, inclusive, indicated that
legal-sized whitefish were most abundant in Lake Huron at depths of 81 to 110 feet
with the peak concentration in 91 to 100 feet. Illegal-sized fish were most abundant in
71 to 110 feet with a maximum concentration at 81 to 90 feet, 10 feet shallower than the
depth of greatest abundance of legal fish. The records for the grounds off Alpena and
in the Saginaw Bay area suggest that both legal- and illegal-sized whitefish may move
onshore during the summer and return to deeper water in the autumn.
10. The whitefish lives in shallower water in northern Lake Michigan than in Lake
Huron. The averages for the entire season (May to October, inclusive) showed legalsized
whitefish to be most abundant in 71 to 110 feet (peak concentration at 81-90
feet) and illegal-sized fish in 61 to 110 feet (peak at 71-80 feet). The depths of the
peak concentrations were 10 feet shallower in northern Lake Michigan than in Lake
Huron for fish of corresponding size.
11. The records for the individual months indicated that both legal- and illegalsized
whitefish in northeastern Lake Michigan moved toward deeper water from June
to September. The October data provided some indication of a return migration in
the autumn. These movements are the reverse of those indicated by the data for the
Lake Huron whitefish.
12. The vertical distribution of whitefish in northeastern Lake Michigan was characterized
by the presence of two concentration zones of both legal- and illegal-sized fish..
Although the actual depths at which the zones occurred varied from month to month
with the offshore and onshore movements of the fish, the two concentrations remained '