Analysis of Fish Assemblage Data
of Thunder Bay, Alpena MI

Scott R. Koproski
School of Science and Natural Resuorces
Lake Superior State University
Sault Ste. Marie MI 49783


	The ruffe (Gymnocephalus cernus) is an exotic species of great concern in the
Great Lakes. It was first discovered in Duluth Harbor in 1986, and by 1992 the
population numbered 1.8 million. Ruffe expansion could have serious ecological
and economic impacts for existing fish communities due to competition for food
resources. Two species of grave concern are the yellow perch (Perca flavescens)
and walleye (Stizostedion vitreum). Ruffe have been shown to forage on eggs
produced by these and other species. Because of these effects, failure to prevent
dispersal of ruffe from Lake Superior has potential to significantly impact the
perch and walleye fishery in Saginaw Bay, Lake St. Clair, and Lake Erie.
	This study was the first year of an on going study to identify the fish
assemblage in Thunder Bay, Ml, a midway point between Duluth Harbor and the
lower Great Lakes. Four different gear types were used to collect fish: gillnets,
experimental gillnets, a bottom trawl, and a DC electro-fishing boat. This
combination of gear types was used because no single gear type can adequately
sample all species and sizes of fish. Identifying the fish assemblage in Thunder
Bay before the invasion ofthe ruffe allows monitoring of this system should the
ruffe invade. Relative abundance and diversity, using the Shannon-Weaver Index,
of species caught at each site and by each gear type were estimated. Both site 1,
which had the best habitat out of the three sites, and the experimental gillnets,
which had mesh ranging fiom I .5 inches to 3.5 inches, had the greatest relative
abundance of fish and the greatest diversity of species.
	As of 1 994, no ruffe were found outside Lake Superior, but in I 995 and 1996,
respectively, 36 ruffe were collected in Thunder Bay. Ifrufte are allowed to
invade the lower Great Lakes as easily as they did Lake Superior, they could have
serious impacts on the nearshore fisheiy, pa~cularly for yellow perch and
walleye.

Literature Cited:
Ogie. D.H.. J.H Selgcbv. J.F. S(I\iHo. R.M. Newm~n. (md M.G. Hcn~. ~996.
Pred~tion on Ruffe bv N(~ti\c Fishes ofthe St. Lotus River Estu(~PN'. L~ke
Superior. I 9~9- 1 ()9 I . North Amenc~~n JOtl~(iI of Fishenes M~~n~gement
16: ~15-[23.
We3\er, M.J.. J.J. M~~gntisoii. (~fld M.K. C1~yton. 1993. Aii~Ivsis for
Differeflti(ltiflg Littor~I Fish Assemb1~igcs with C~tch D~1(~ from Multiple
S(lmpliug Ge~rs. Tr(ifls(~ctiofls of tI)e Anicric~n Fishenes Society 1 1 2:
1111-I I I~).