U. S. Geological Survey, Lake Superior Biological Station, 2800 Lake Shore Drive East Ashland, Wisconsin 54806

Summary

         Status and trends of the fish community of the inshore waters of Lake Superior (<80 m depth, <5 km from shore) were monitored through annual bottom trawl surveys conducted around the perimeter of the Lake during 1978-2003 in U.S. waters and 1989-2003 in Canadian waters. Of 35 species captured over the 26-year period, 17 were commonly caught and represented 99.4% of the total community biomass. Four prey species, lake herring (Coregonus artedi), bloater (Coregonus hoyi), lake whitefish (Coregonus clupeaformis), and rainbow smelt (Osmerus mordax), represented 76.3% of the total community biomass. At the start of the monitoring period, biomass and commercial yields of the exotic rainbow smelt were at historic highs while biomass and commercial yields of native lake trout (Salvelinus namaycush), lake whitefish and lake herring were at historic lows because of decades of overharvest and depredation by the exotic sea lamprey (Petromyzon marinus). In an effort to reverse the declines in native fish stocks, management agencies implemented lamprey control programs, lake trout stocking programs, and closed or restricted commercial trout fisheries in the 1960s and 1970s. The structure of the Lake Superior fish community changed considerably over the 26-year monitoring period. During the first phase (1978-1979), the inshore fish community was dominated by non-native species: rainbow smelt was the principal prey fish and accounted for ~50% of the total community biomass, and planted hatchery strains of lake trout were the principal predator and accounted for ~10% of total community biomass. The second phase (1980-1983) was marked by a transition in community structure: biomass of rainbow smelt populations declined sharply while wild lake trout populations rebounded and small, but successful new cohorts of lake herring began to emerge. The appearance of the large 1984 lake herring year-class and a rapid increase in wild lake trout biomass signaled the beginning of the third phase of the Lake Superior fish community. During 1984-1996, recovery of the native fish community became evident; biomass of lake herring, bloater, lake whitefish, and wild lake trout (lean and siscowet) increased while biomass of rainbow smelt increased over levels observed during the transition period, but remained well below their 1978-1979 level. After 1996, the fish community entered the final phase in which biomass of the principal prey species, lake herring, and wild lake trout gradually declined, and by 2003 approached the low levels observed in 1980-1983. Primary factors that affected the structure and dynamics of Lake Superior fish communities since 1978 included recovery of wild lake trout and lake herring populations and the decline in dominance of rainbow smelt populations. Rapid shifts in community structure were linked to recruitment of large year classes of lake herring and a sharp increase in mortality of rainbow smelt. Changes in the structure of the Lake Superior fish community are likely to continue in the future as lake trout populations continue to evolve in response to new conditions, and fishery managers implement new strategies to continue the restoration of prey fish populations.