Effects of discharge on daytime habitat use by muskellunge in the New River, Virginia

For several fish species, increased river discharge has been linked to behavioral changes, including movement towards particular habitats. From 2000 to 2003, we used radiotelemetry to monitor habitat use by 42 muskellunge Esox masquinongy within a 17‐km reach of the New River, Virginia; to evaluate habitat selection; and to determine whether habitat use and selection were affected by discharge. Water depth, occurrence of aquatic vegetation, substrate type, and distance to riverbanks within the study reach were mapped with hydroacoustic and Global Positioning System technologies. Real‐time discharge measurements from an upstream U.S. Geological Survey stream gauge were used to classify fish locations into those made during periods of reduced (<75 m3/s) or increased (>75 m3/s) discharge. Seasonal habitat selection models for the different discharge levels were created using logistic regression. Differences in logistic regression coefficients between models were tested with multivariate chi‐square tests and Bonferroni‐corrected pairwise comparisons. Meta‐analytic averaging of Pearson’s correlation coefficients was used to determine the overall effect size of discharge on habitat use by muskellunge. Overall, muskellunge exhibited a positive selection for deeper habitats; however, discharge was found to significantly affect both habitat use and selection. Habitat use was consistent with the hypothesis that fish moved to shallower habitats (both summer and winter) located closer to riverbanks (winter only) during periods of increased discharge. In terms of habitat selection, selection strengths for variables such as water depth (summer and winter) and distance to shoreline (winter only) generally weakened during periods of increased discharge, indicating that habitat use became more proportionate to availability. Increased movement as a result of increased discharge has been theorized to potentially reduce winter survival of fish because of seasonal energetic limitations. Thus, indirect effects on fish from dam operating modes (e.g., hydropeaking) may be as important as direct effects when evaluating biotic implications of water release schedules.