Landscape character and fish assemblage structure and function in western Lake Superior streams: General relationships and identification of thresholds

• Published in: Environmental management (New York) 2004-06, Vol.33 (6), p.855-875
• Main Authors: BRAZNER, John C, TANNER, Danny K, DETENBECK, Naomi E, BATTERMAN, Sharon L, STARK, Stacey L, JAGGER, Leslie A, SNARSKI, Virginia M
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Biological and medical sciences; Conservation, protection and management of environment and wildlife; Environment; Environment Design; Environmental management; Environmental Monitoring; Fish; Fishes; Freshwater; Fundamental and applied biological sciences. Psychology; General aspects; Geological Phenomena; Geology; Great Lakes Region; Habitats; Lake basins; Lakes; Land use planning; Pisces; Population Dynamics; Regression analysis; Seasons; Streams; Water Movements; Watersheds
• ISSN: 0364-152X; 1432-1009
• DOI: 10.1007/s00267-004-3031-0

As part of a comparative watershed project investigating land-cover/land-use disturbance gradients for streams in the western Lake Superior Basin, we examined general relationships between landscape character and fish assemblage structure and function. We also examined the shape of those relationships to identify discontinuity thresholds where small changes in landscape character were associated with marked shifts in the fish assemblages. After completing a geographic analysis of second- and third-order watersheds in the western Lake Superior drainage, we randomly selected 48 streams along mature forest and watershed storage gradients in 2 hydrogeomorphic regions as our study sites. During the summers of 1997 and 1998, we used electrofishing to sample fish assemblages from each stream. Each of the landscape factors was significantly associated with fish assemblage structure and function based on analysis of covariance. Watershed storage was related to the greatest number of fish assemblage characteristics, but hydrogeopmorphic region and mature forest cover were strongly associated as well. The hydrogeomorphic region also mediated relationships between watershed character and fish assemblages. Discontinuity thresholds for our fish assemblages averaged 11% for watershed storage and 50% for watershed mature forest cover based on piecewise regression analysis. Although many of the landscape-fish relationships might have been manifest through effects on in-stream habitat, our results highlight the importance of management and land-use planning decisions at the watershed and landscape scales.