the locks on the St. Marys River to 31 January 2
(1986) were able to compare the extent of macro-
phyte beds in the SCDRS before and after a mas-
weeks. Since navigation throughout the winter
sive ice jam in April 1984. Little change was noted
was already occurring on the SCDRS, they pre-
in macrophyte beds due to this severe ice event,
sumed that the existing fish population was per-
as noted earlier.
sisting without any severe stress from prior lev-
The potential effects of suspended solids in-
els of shipping and limited their speculations to
cluded siltation of spawning beds, decreased pro-
the potential effects of increased winter vessel
ductivity, reduced food availability, clogging of
traffic.
gills, reduced respiration and changes in behav-
A total of 57,579 fish of 57 species and three
ior. Liston and McNabb (1986) mentioned that high
hybrids were identified during the study. The pre-
turbidity is generally recognized as an acute stress
dominant species included rock bass, yellow perch,
that fish can tolerate for short periods of time and
walleye and white perch. They also made spawn-
that they may migrate away from it. As discussed
ing condition determinations on 23 species. Yel-
earlier in this report, there has not been substan-
low perch comprised 66% of the fish observed in
tive documentation of large or persistent increases
spawning condition, followed by rock bass (14%)
in turbidity during ship passage on the Great Lakes
and white bass (8%). There was no apparent cor-
connecting channels. Liston and McNabb (1986)
relation with the species composition of fish eggs
also cited documentation where several species
and larvae determined by Muth et al. (1986), in
of fish were exposed to very high levels of sus-
which alewife, smelt and logperch comprised the
pended solids (as high as 20,000 ppm) and tur-
bulk of the eggs collected, while larvae were domi-
bidity (up to 500 NTU) without abnormal behav-
nated by alewife, gizzard shad, white perch and
ior or apparent harm.
emerald shiner.
These levels are far in excess of those observed
A fish tagging and creel survey effort showed
by Poe et al. (1980), Sletten (1986) or Hodek et al.
that the combined shore and boat angling effort
(1986) for ship passages on the St. Marys, St. Clair
in the U.S. waters of the SCDRS averaged 810,000
and Detroit Rivers. Liston and McNabb (1986)
hours on the St. Clair River, 1,409,000 hours on
found ambient turbidity levels at their sites on
the Detroit River and 1,953,000 hours on Lake St.
the St. Marys River to range from 1.3 to 45.5 NTU
Clair. The average annual harvest was 164,000 fish
during the summer and 0.5 to 2.3 NTU in the
from the St. Clair River, 1,421,000 from the De-
winter. For ship passages monitored during the
troit River and 1,198,000 from Lake St. Clair. A
open-water season, no reading exceeded 11.8 NTU.
total of 29,168 fish of 43 species were tagged dur-
The measurements of Hodek et al. (1986) on the
ing the study to gather information on movements,
St. Marys River showed typical ambient turbid-
exploitation and abundance. Angler tag returns
ity levels of 530 JTU, with a maximum reading
during the period from December through March
of 380. During vessel passages their measurements
constituted only 10% of the total 1,081 returns by
typically ranged from 6 to 30 JTU, with a maxi-
sport and commercial fishermen. Ice angling was
mum of 53. On the Detroit and St. Clair Rivers,
determined to account for only 12% of angling
Sletten (1986) reviewed the Environmental Pro-
hours and 17% of the total catch.
tection Agency STORET database and estimated
Haas et al. (1985) considered potential impacts
that mean turbidities varied from 7.3 JTU in the
of winter navigation on both the fish community
summer to 8.7 in the winter. Sletten also moni-
and the winter angling fishery. They felt that fish
tored turbidity during 42 ship passages and found
spawning and food availability might be influ-
maximum levels ranging from 2.3 to 73 JTU. The
enced by physical disruption of critical habitats
maximum turbidity measured during his "win-
by ice gouging and that additional vessel pas-
ter" field periods (April and December 1984) was
sages could alter patterns of ice formation that
7 JTU. Liston and McNabb (1986) concluded that
might interfere with ice fishing activities. Although
suspended solids levels in the St. Marys River
considered less likely, they also mentioned the
would cause no direct harm to the fishery unless
possibility of interference with fish migration. The
catastrophic increases in sediment load occur.
significance of each of these effects was consid-
Haas et al. (1985) studied the movement and
ered to decrease with distance from the naviga-
harvest of adult fish in the SCDRS during 1983
tion channel.
and 1984. The objective of the study was to de-
While they provided no documentation or
scribe the existing adult fish community and to
speculation as to the significance of their proposed
consider any potential impacts from operation of
impact mechanisms, their observations on fish be-
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