Fish Biomass in Relation to Stream Condition and Connectivity in the Mid-Atlantic

Biomass is a fundamental ecosystem property, integrating physiological, environmental, top-down and bottom-up effects. We used depletion sampling to determine the biomass of fish assemblages from streams of the Delaware River drainage. We will examine relationships among stream size, land cover, and biomass of different species. These sites cover a range of stream conditions and include sites with American eel and sites where eels are blocked by downstream dams. Preliminary analyses using 2013 monitoring data indicate that total biomass at many sites increased with development and was correlated with diatom-based nutrient indices, consistent with expectations from effects of nutrient enrichment and increased light. However, the increase was evident mainly in streams accessible to eels, where eels comprised a large part of total biomass. American eel comprised a small part of biomass in small, forested streams. These results, if general, imply that a large part of the increased biomass from bottom-up effects go to eel biomass.  We will apply the analysis to a greater range and number of sites, including some with data taken before and after dam removal, expand the analysis to more potential explanatory variables, and examine accuracy and bias of different methods of estimating biomass from depletion data.