The soft-bottom benthic fish community of the St. Louis River and Duluth-Superior Harbor was examined yearly (20 of 23 years) from 1989 through 2011 using bottom trawling. Catch per unit effort (CPUE) and fish lengths were used to assess the impact of the round goby, which appeared in trawl records in 1998, on benthic native fishes. Logperch (Percina caprodes), spoonhead sculpin (Cottus ricei), johnny darter (Etheostoma nigrum), channel catfish (Ictlarus puncatus), tadpole madtom catfish (Noturus gyrinus) and bullhead catfish (Ictalurus spp.) plus the invasive Eurasian ruffe (Gymnocephalus cernuus) populations were assessed. After detection in the trawl record in 1998, round goby continued to increase in abundance through 2006. Logperch showed a 65% decline in median CPUE from 2.4 to 0.85, while johnny darter increased almost three-fold from 0.24 to 0.68 CPUE following round goby detection. Bullheads dropped from 7.5 CPUE to being virtually extirpated from the study area. However, their decline preceded round goby appearance, and was linked to the stocking of predator fish to combat the Eurasian ruffe. It is hypothesized that the presence of the Eurasian ruffe contributed to depressing the native fish population to the extent that the round goby appearance had less impact on the community. However, after 20 years of decline, the native fish appear to be rebounding due to declines in the Eurasian ruffe and round goby populations and improvements in water quality.
Bibliographical noteFunding Information:
We would like to acknowledge the United States Geological Survey, the Environmental Protection Agency and the 1857 Treaty Authority for providing access to their trawl records. Funding for the research was partially provided by the Minnesota Environmental Trust Fund. Thanks to B. Vetter and K. Murchy for providing helpful comments on the manuscript and T. Hrabik for assistance with statistical analysis.
© 2016 International Association for Great Lakes Research.
Copyright 2017 Elsevier B.V., All rights reserved.
- Eurasian ruffe
- Invasive fish