Multi-Scale Habitats and Stressors Influencing Lake Pontchartrain Basin Stream Fish Assemblages

This study assessed hierarchical relationships among reach, subwatershed  and watershed characteristics that structure fish assemblages the Lake Pontchartrain Basin, Louisiana and Mississippi. Reach-scale habitat (i.e., instream and riparian) had the strongest association with the assemblage, after removing potential interactions among spatial structure and environmental variation from subwatershed and watershed data (Partial redundancy analysis; 13.5% variation explained).   Channel width, depth, aquatic vegetation, human debris, rapid habitat assessment (RHA) score, and large woody debris volume were the most important variables at the reach scale.  At the subwatershed (pRDA; 9.2%) and watershed scales (pRDA; 12.8%), geomorphic characteristics were important, including elevation, gradient, watershed area, wetland cover and stream density.  Stressors included dam and oil/gas well densities.  Cumulative fit statistics from the pRDA plots revealed that 23 species were influenced primarily by reach-scale habitats, including two rare species.  One species was influenced most by subwatershed characteristics, while six species showed greater variation in abundance with watershed-scale factors.  Species exhibiting greater variation with a particular spatial scale tended to have similar life history characteristics.  For example, the species associated with watershed factors had life spans less than four years, egg diameters less than 2 mm, spawning periods greater than three months, and were foraging generalists.