Project
Evaluating vessel avoidance during acoustic/trawl surveys of pelagic forage fish using a hybrid research vessel
Annual acoustic/trawl surveys on the Great Lakes assess fish populations but are subject to bias due to fish behavior and gear limitations. Near-surface fish are difficult to detect with hull-mounted transducers and difficult to capture with nets due to vessel avoidance, and the target strength of individual fish decreases as fish dive to avoid vessel noise, which can bias biomass estimates. Avoidance may increase with vessel-noise intensity, yet even noise-reduced vessels under diesel propulsion can still elucidate significant avoidance responses in fish. We are conducting in-lake experiments to quantify vessel avoidance by coupling up-looking echosounders on the bottom of Lake Champlain with a hybrid diesel-electric research vessel. Our study is unique because using the same ship under different engine propulsion systems allows us to separate the effects of engine vs hull noise on fish avoidance behavior and subsequent acoustic and trawl estimates. Improved estimates of pelagic fish populations will provide better assessments of predator-prey balance, impacts of management actions, and factors influencing population dynamics of important prey fishes.