Tuesday, May 27, 2008
330

Effects of low-head dams on crayfish assemblages in Alabama streams

Emily E. Hartfield, Biological Sciences, Auburn University, 331 Funchess Hall, Auburn, AL 36849, Jack W. Feminella, Department of Biological Sciences, Auburn University, 331 Funchess Hall, Auburn, AL 36849, and Michael M. Gangloff, Biology, Appalachian State University, 572 Rivers Street, Boone, NC 28608.

Dams affect stream habitats by altering temperature regimes, water chemistry, hydraulic and sediment regimes, and channel morphology.  In addition, these impoundments can impede upstream movements of migratory organisms, such as stream fishes, and cause accumulations of individuals directly downstream of dams.  Effects of large dams on the physical and biotic properties of streams have been well documented, whereas effects of small, low-head dams on streams are comparatively less understood.  Low-head dams, such as mill dams, are widespread in many southeastern US streams and have the potential to affect many imperiled fishes and benthic invertebrates.  In 2006 and 2007 we quantified crayfish and their habitats in 6 Alabama drainages, comparing populations at upstream, immediately downstream, and > 500m downstream reaches of 3 low-head mill dams (2 intact, 1 breached) per drainage.  Preliminary data suggested that crayfish abundance and richness were lower and species composition different immediately downstream of most intact dam sites compared with upstream and further downstream sites.  In addition, some populations upstream of dams showed strongly dissimilar size distributions than downstream populations.  We hypothesize that changes in physicochemical conditions, disrupted upstream movement, and aggregation of predacious fishes brought about by intact dams are responsible for these patterns.


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