RELATIVE ABUNDANCE AND DISTRIBUTION OF RUFFE (GYMNOCEPHALUS-CERNUUS) IN A LAKE SUPERIOR COASTAL WETLAND FISH ASSEMBLAGE

Fish assemblages from Allouez Bay Wetland in the St. Louis River estua ry were sampled with fyke-nets from May to October, 1995, to character ize typical use patterns in different seasons and microhabitats. The r elative abundance and distribution of ruffe (Gymnocephalus cernuus) in these habitats was of interest because their recent invasion into the Great Lakes has the potential to disrupt native fish assemblages. A t otal of 15,867 fish comprised of 34 species were captured in 2,300 h o f netting. The majority of fish over the whole study were caught in th e outer marsh (63%, 9,957 individuals), and seasonally during late Jun e (7,384 individuals/4 net-nights) and early May (2,281 individuals). Yellow perch (Perca flavescens), brown bullhead (Ameiurus nebulosus), emerald shiner (Notropis atherinoides), and silver redhorse (Moxostoma anisurum) were the most abundant species, comprising 85 percent of th e total catch. Ruffe was the seventh most abundant species captured (2 94 individuals), comprising only two percent of the total catch. They were the fifth most abundant species in the outer marsh, but only thir teenth most abundant in the inner marsh. Ninety-one percent of all ruf fe (268 individuals) were caught in the outer marsh. Of the 75 species by life-stage combinations derived by classifying all individuals cap tured into one of 3 life stage categories (YOY, yearling, and adult), yearling ruffe were the twelfth h most abundant, adult ruffe were sixt eenth, and YOY ruffe were twenty-seventh. While ruffe have been rite m ost abundant fish captured in bottom trawls in St. Louis River estuary during the 1990s, our results indicate the invasion of ruffe in shall ow, heavily vegetated areas like those in Allouez Bay has been much le ss successful. Our results also suggest further degradation of coastal wetlands and other vegetated habitats would eliminate significant ref ugia from ruffe competition and could lead to increased dominance of r uffe in shallow water habitats in the Great Lakes.