Effect of Discharge on Daytime Habitat Use and Selection 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 m/s) or increased (.75 m/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 Bonferronicorrected 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. The muskellunge Esox masquinongy is a primarily piscivorous fish species having a native range restricted to the Mississippi, Ohio, St. Lawrence, and Tennessee River drainages of North America (Crossman 1978). Due to its popularity as a sport fish, though, the muskellunge has been introduced throughout North America (Crossman 1986). In the southeastern United States, the muskellunge has been introduced to water bodies in Alabama, Arkansas, Georgia, Kentucky, North Carolina, South Carolina, Tennessee, Virginia, and West Virginia (USGS 2004a). Some of the most productive muskellunge fisheries resulting from these introductions have been in riverine environments due possibly to factors such as greater food availability (Harrison and Hadley 1979) or cooler water temperatures. In Virginia, the top trophy-producing muskellunge fisheries (trophy muskellunge size in Virginia is designated as 1,016 mm or 6.8 kg) have been the New and James rivers. From 1990 to 2003, these rivers produced 58% (n 1⁄4 546) of trophy muskellunge registered with Virginia’s Angler Recognition Program, the remaining number divided among 20 other lakes, reservoirs, and rivers (Virginia Department of Game and Inland Fisheries [VDGIF], unpublished data). Despite the recreational opportunities provided by riverine muskellunge fisheries in the southeastern United States, very little regional research related to muskellunge biology and ecology in rivers has been conducted. The only information regarding muskellunge habitat use in southeastern U.S. rivers comes from descriptions of fish sampling locations (Parsons 1959; Miles 1978; Brewer 1980; Axon and Kornman 1986; Monaghan and Borawa 1988). The ability to link such descriptions to actual habitat selection, though, is premised on sampling being equally effective across habitat types, an assumption that rarely is met. Boat electrofishing, which often is used to sample muskellunge in rivers (Miles 1978; Axon and Kornman 1986; Monaghan and Borawa 1988), is generally effective over a limited range of water depths (Reynolds 1996). Electrofishing also is often conducted exclusively along riverbanks; thus, it may not be known to what * Corresponding author: [email protected] 1 Present address: Quantitative Fisheries Center, Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan 48824-1222, USA. Received October 24, 2005; accepted June 22, 2006 Published online November 9, 2006 1546 Transactions of the American Fisheries Society 135:1546–1558, 2006 Copyright by the American Fisheries Society 2006 DOI: 10.1577/T05-256.1 [Article]