Combining Split-Beam and Dual-Frequency Identification Sonars to Estimate Abundance of Anadromous Fishes in the Roanoke River, North Carolina

Abstract

Riverine hydroacoustic techniques are an effective method for evaluating abundance of upstream migrating anadromous fishes. To use these methods in the Roanoke River, North Carolina, at a wide site with uneven bottom topography, we used a combination of split-beam sonar and dual-frequency identification sonar (DIDSON) deployments. We aimed a split-beam sonar horizontally to monitor midchannel and near-bottom zones continuously over the 3-month spring monitoring periods in 2010 and 2011. The DIDSON was rotated between seven cross-channel locations (using a vertical aim) and nearshore regions (using horizontal aims). Vertical deployment addressed blind spots in split-beam coverage along the bottom and provided reliable information about the cross-channel and vertical distributions of upstream migrants. Using a Bayesian framework, we modeled sonar counts within four cross-channel strata and apportioned counts by species using species proportions from boat electrofishing and gill netting. Modeled estimates (95% credible intervals [CIs]) of total upstream migrants in 2010 and 2011 were 2.5 million (95% CI, 2.4–2.6 million) and 3.6 million (95% CI, 3.4–3.9 million), respectively. Results indicated that upstream migrants are extremely shore- and bottom-oriented, suggesting nearshore DIDSON monitoring improved the accuracy and precision of our estimates. This monitoring protocol and model may be widely applicable to river systems regardless of their cross-sectional width or profile.

Received July 16, 2014; accepted November 21, 2014

ACKNOWLEDGMENTS

Funding for this project was provided by Dominion Power Company and the North Carolina Wildlife Resources Commission. We thank fisheries technicians Joshua Ashline and Jacob Johnson for field assistance, Anna-Marie Mueller and Don Degan of Aquacoustics for hydroacoustic training and guidance, and Charlton Godwin of North Carolina Division of Marine Fisheries for providing monthly catch data from netting surveys. This manuscript benefited from the comments of Carolyn Griswold and two anonymous reviewers. The Cooperative Fish and Wildlife Research Unit is jointly supported by North Carolina State University, North Carolina Wildlife Resources Commission, U.S. Geological Survey, U.S. Fish and Wildlife Service, and Wildlife Management Institute. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Sampling was conducted under Institutional Animal Care and Use Committee protocols 08-008-O and 11-037-O.