The Great Lakes Fishery Commission monitors and/or maintains >1000 barriers in watersheds draining to the Great Lakes for the purpose of restricting sea lamprey access to spawning habitat. Although a critical aspect of sea lamprey control, growing concern over the impacts of bi-directional blockage on native fishes has prompted considerable interest in the retrofitting of existing barriers with fish passage devices (per GLRI Action Plan II). The best design for a sea lamprey-blocking fishway will have two features: (1) the ability to entrain and selectively remove migrating sea lamprey whilst (2) passing native and desirable fishes, an approach we term ‘Pass-and-Trap’. Behavioral differences between anguilliform lamprey and fusiform fishes may allow for such a design. Specifically, recent evidence suggests a channel equipped with a vertical-slot fishway and emitting a natural repellent may block sea lamprey and allow natives to pass, whereas an adjacent channel equipped with an eel-ladder and trap may capture sea lamprey whilst blocking native fishes – effectively removing sea lamprey from the fishes moving through the fishway without manual sorting. We will test the viability of this design in a two-channel model fishway. Our test designs will be informed by lessons-learned from detailed examination of successes and failures to pass migrating lampreys through European fishways and attempts to capture them in traps with eel-ladders in the Great Lakes. The results will be used to develop design criteria to retrofit existing fish passage devices at sea lamprey barriers into ‘Pass-and-Trap’ designs.
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