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REGIONAL, WATERSHED, AND SITE-SPECIFIC ENVIRONMENTAL INFLUENCES ON FISH ASSEMBLAGE STRUCTURE AND FUNCTION IN WESTERN LAKE SUPERIOR TRIBUTARIES
Citation:
Brazner, J. C., D K. Tanner, N E. Detenbeck, S L. Batterman, S. L. Stark, L. A. Jagger, AND V M. Snarski. REGIONAL, WATERSHED, AND SITE-SPECIFIC ENVIRONMENTAL INFLUENCES ON FISH ASSEMBLAGE STRUCTURE AND FUNCTION IN WESTERN LAKE SUPERIOR TRIBUTARIES. CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES. National Research Council Canada, 62(6):1254-1270, (2005).
Description:
The relative importance of regional, watershed, and in-stream environmental factors on stream fish assemblage structure and function was investigated as part of a comparative watershed project in the western Lake Superior basin. We selected 48 second and third order watersheds from two hydrogeomorphic regions to examine fish assemblage response to differences in ecological region, forest fragmentation, watershed storage, and number of other watershed, riparian and in-stream habitat conditions. Electrofishing was used to sample fish from second order streams in 1997 and third order streams in 1998 during summer baseflow conditions. Floodplain, riparian, and in-stream habitat variables were measured at 13 transects within each reach following fish sampling. Although a variety of regional, fragmentation, and storage related factors had significant influences on the fish assemblages, water temperature appeared to be the single most important environmental factor. We found lower water temperatures and trout-sculpin assemblages at lower fragmentation sites, and while fishes with higher silt tolerances, warmer temperature preferences, weaker sustained swimming capabilities, and general current preferences were most common at higher storage sites. Our results suggest site-specific environmental conditions are highly dependent on regional higher temperatures and minnow-sucker-darter assemblages as storage increased. Factors related to riparian shading and flow separated brook trout streams (shaded/lower flow) from brown/rainbow trout streams (less shaded/higher flow). Functionally, fish assemblages at lower fragmentation sites were dominated by coldwater fishes that had low silt tolerance and preferred moderate current speeds, and watershed scale characters and that a combination of these factors operate in concert to influence the structure and function of stream fish assemblages.