typically 36F cooler in 1983. The Detroit River
behavior. Waterfowl and raptors were observed
is typically about 5F warmer than the St. Clair
on 60 days between January and April 1979. About
River during May through July, when many spe-
1000 ducks were present in January, declining
cies spawn.
slightly in February due to emigration, and in-
Interestingly the mean monthly water tempera-
creasing again in late March. The most frequently
tures collected at the water intakes for the cities
observed raptors were a pair of adult bald eagles.
of Port Huron and Detroit cited by Hudson et al.
Bird mortality appeared to be very low during
(1986) as a possible cause of the lower abundance
the winter of 1978-79 (no dead birds were found)
of macrophytes, benthos and fish in 1984 directly
despite unusually harsh weather.
conflicts with the trends used by Muth et al. (1986)
Critical areas occupied by wintering duck
to explain lower egg and larvae abundance in 1983.
populations were identified as the St. Marys Rap-
Mean monthly water temperatures near Port Hu-
ids, the Edison Soo hydroplant outfall and open-
ron on the St. Clair River were higher for 1983
water stretches along the Canadian shore near
than for 1984 during April, May, July and Sep-
Sault Ste. Marie. Open water in the shipping lanes
tember and were equal during June and August.
was scarcely used by ducks, perhaps due to a lack
On the Detroit River near Belle Isle, 1983 tem-
of food there. For eagles, two perch areas along
peratures were higher from May through Octo-
the northeast shore of Sugar Island were found
ber, with the exception of June, when the 1984
to be important. The direct impact of the 425 ves-
temperature was 2F higher.
sel passages that occurred during the study pe-
Because only three species of fish identified
riod was considered minor, with flushing of birds
during their study spawn during fall or winter
being the only observed effect. In virtually all in-
(and none were abundant in their samples), Muth
cidents where ducks were flushed by ships, the
et al. (1986) felt that it was highly unlikely that
number of ducks did not return to their pre-pas-
extended season navigation would destroy sig-
sage levels. During the colder months, however,
nificant numbers of fish eggs or recently hatched
both ducks and eagles tended to avoid the ship-
larvae. They did, however, speculate on the po-
ping lanes and incidents of flushing were rare.
tential for adverse impact due to habitat alter-
By April, with more open water and more ships,
ation. They suggested that increased shipping
the number of incidents increased dramatically.
could result in increased ice accumulations and
The metabolic significance of flushing, because
movement that could scour spawning sites and
of energy expenditures, remains unknown. How-
reduce available habitat. Such scouring, however,
ever, most flushing takes place in April (during
has not been documented. They also felt that ex-
the regular shipping season) when food resources
tended season navigation could alter water tem-
are being uncovered and are becoming available.
peratures by facilitating or delaying ice breakup
The influence of ship-induced turbidity and
or jamming. If water temperatures were altered,
ice scouring of vegetation on duck foods, and the
the impact could be either positive or negative.
possibility of spills of oil or toxic materials, were
Although a major jam occurred during their pe-
cited as potential effects but were not assessed,
riod of study, and significant shipping and
and no data were presented. The potential for
icebreaking activities took place during its three-
scouring of vegetation by ice has been consid-
week duration, they did not attempt to directly
ered by Liston and McNabb (1986) and discussed
address its impact on egg and larvae populations.
in the section of this report on aquatic plants.
Hudson et al. (1986) also described the 1984 ice
jam on the St. Clair River and its impact on aquatic
Birds
The potential effects of winter navigation on
plants. The potential for oil or toxic material spills
waterfowl and raptorial birds were studied by
is addressed in a separate part of this report.
Robinson and Jensen (1980) in the vicinity of the
Although the critical open-water areas cited
St. Marys River as part of the FY79 Environmen-
in the report have not been sampled, studies by
tal Effects Working Group program. The objec-
Hodek et al. (1986), Sletten (1986), Gleason et al.
tives were to describe the species and numbers
(n.d.) do not support large or persistent increases
of waterfowl and raptors in the area, to define
in turbidity during vessel passages. This would
areas used by resident and migrating populations
appear to be particularly true for sites isolated
along with the frequency of visits and their ac-
from the navigation channel, such as the St. Marys
tivities while observed, and to analyze the effects
Rapids and pools along the Canadian shoreline.
of winter-navigation-related activities on bird
Further, the lack of an ice cover in these areas is
35
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