Fish-continue - CR95

havior are relevant. They noted that their data

before (1983) with those after the ice jam. This

on winter fish distribution in the SCDRS suggest

jam represents perhaps a worst-case scenario for

that fish generally move to overwintering areas

ice effects. Fish catches were usually lower in 1984

in the fall and that wintertime movement rates

in both rivers, but Hudson et al. did not consider

are low. From their fish tagging and net catch data

the difference to be statistically significant. They

they further concluded that fish concentrations

felt that the lower catches may have been due to

are substantially reduced in the vicinity of the

the effect of lower water temperatures on the de-

channels and that fish that remain near the navi-

velopment of plant beds, general activity level

gation channel seek out the adjacent marshes and

and seasonal migrations.

channels as overwintering sites. They also noted

Muth et al. (1986) conducted a study on the

that the angler effort and harvest on the SCDRS

SCDRS to provide baseline information on the

were quite low in winter with the exception of

abundance and distribution of fish eggs and lar-

the yellow perch fishery. That fishery was con-

vae and to assess potential impacts on fish re-

centrated in Anchor Bay, an apparent wintering

production that might occur from extending the

area, which is well away from the navigation

lock operation season on the St. Marys River.

channel. Further, much of the St. Clair and De-

Analyses of the distribution and abundance of

troit Rivers remain ice free, limiting ice fishing

the eggs of 19 species and the larvae of 29 species

opportunities.

suggested that abundance varied significantly

To evaluate the validity of their postulated im-

between the St. Clair and Detroit Rivers and be-

pact mechanisms, they proposed that a two-year

tween the 1983 and 1984 data collection seasons.

study take place if the season were extended to

The number of eggs collected from the Detroit

evaluate possible impacts on fish and furbearers.

River (22,000) was more than 2.5 times greater

They suggested that such a study should be con-

than from the St. Clair (8,974). Rainbow smelt eggs

centrated on the St. Clair River, where they felt

dominated the St. Clair River samples, while those

that winter shipping would have the most influ-

of gizzard shad and white bass dominated samples

ence on fish and the sport fishery. Data from that

from the Detroit River.

effort could be compared with the information

Egg abundance was less in 1983 than in 1984

from their present report, which would serve as

for both rivers. Fish larvae were also less abun-

a baseline. Since their combined catch of nine

dant in 1983, but the difference was greater for

selected species varied approximately 28% from

the St. Clair River. Alewives were the most abun-

1983 to 1984, however, they noted that extended

dant larvae in both rivers during both years. The

season operations would have to cause even

larvae of rainbow smelt, various darters and

greater changes in the fish population to be de-

logperch were also abundant in the St. Clair River,

tectable. Further, since winter trap net catches

while gizzard shad and emerald shiners were

yielded only about 8% of those during summer

abundant in the Detroit River. The distribution

high-catch periods, it would be difficult to make

of larvae varied significantly between rivers, sites,

judgments about winter fish behavior.

months and study years.

Hudson et al. (1986) captured 1771 fish of 36

Muth et al. (1986) noted that both water tem-

species in 1983 and 1038 fish of 26 species in 1984

perature and ice conditions can affect the abun-

in the Detroit and St. Clair Rivers during the open-

dance of eggs and larvae. They attributed low egg

water season. The catches were dominated by yel-

and larvae abundance in 1983 to low water tem-

low perch, rock bass, hornyhead chub, spottail

peratures and a slow rate of warming. Although

shiners, striped shiners, rainbow smelt and white

the 1984 ice jam on the St. Clair River probably

suckers. These species made up 86% of the total

delayed fish spawning throughout the system,

catch. They conjectured that the fish communi-

they felt that rapid warming in May and June may

ties observed in their study did not exhibit obvi-

have resulted in greater egg and larvae produc-

ous ill effects from existing levels of winter navi-

tion than in 1983. While the water temperatures

gation. However, winter vessel traffic and other

at their sites on the St. Clair River were compa-

physical changes have occurred for many years,

rable in May of each year, June temperatures were

typically 35F lower in 1983 than in 1984 and

and there was no true baseline from which to judge

prior effects.

July and August temperatures were typically 1

2F lower. Water temperature differences between

As discussed in the section on benthos, how-

ever, a major ice jam on the St. Clair River in 1984

the two years were not as consistent on the De-

afforded an opportunity to compare conditions

troit River, but June and August temperatures were