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Bronte, C.R., L.M. Edwards, W.P. Brown, K.R. Mayo, and A.J. Edwards, 1997. Fish
Community Changes in the St. Louis River, Lake Superior, 1989-1996: Ruffe or Population
Dynamics?, U.S. Geological Survey
Proceedings of the International Symposium on Biology and Management of
Ruffe, March
21-23, 1997
Fish Community Changes in the St. Louis River, Lake Superior, 1989-1996:
Ruffe or Population Dynamics?
Abstract
Introduced ruffe (Gymnocephalus cernuus) have been implicated for the
declines of native species through egg predation and competition for food. From 1989 to
1996, we developed density-estimates of fishes in the St. Louis River estuary (SLRE) to
measure changes in the fish community that may be the result of ruffe. During the study,
ruffe generally increased in abundance while several native species declined. We examined
and compared the declines of the resident stocks to the population dynamics of the same
species from Chequamegon Bay, (an area with very few ruffe) where we had a 25-year record
of density-estimates. From these data, we developed species-specific distributions of
observed trends in abundance as indexed by the slopes of densities across years. From
these distributions and our observed slopes from the SLRE, we estimated probabilities of
measuring negative change at the magnitude observed in the SLRE. Results indicated we had
a good chance of obtaining the negative slopes measured for some species, which suggests
natural population dynamics rather than interaction with ruffe could explain the declines.
For other species, it was unlikely that population dynamics alone could explain the
declines. Variable recruitment rather than mortality of large juveniles and adults was
implicated for most changes in densities of native fish.
Entire Paper
Contact: Charles R. Bronte, U.S. Geological Survey, Biological
Resources Division, Great Lakes Science Center, Lake Superior Biological Station, 2800
Lake Shore Drive, East, Ashland, WI 54806 or charles_bronte@nbs.gov
Keywords: Ruffe, Population_dynamics, Ecological_interactions
Product Type: Publications, Conference_proceedings
User Type: General
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