Wetted Ramps Selectively Block Upstream Passage of Adult Sea Lamprey

Dams fragment stream habitat and fishways around dams typically serve few species that are strong swimmers or jumpers. We test a prototype wetted ramp designed to allow upstream passage of small-bodied fishes while blocking upstream movement of invasive sea lamprey in the Laurentian Great Lakes. We tested short, smooth ramps with 5-10 mm water depth in various combinations of ramp angle, water flow and swim channel width with the aim to selectively block adult migrating sea lamprey while passing sub-adult white suckers (Catostomus commersonii) and creek chubs (Semotilus atromaculatus). Sea lamprey easily passed a 0.75 ramp at 5 angle, but very few individuals passed a similar ramp at 10 angle and none passed a longer ramp at the 5 angle. Limiting the amplitude of tailbeats in a narrow channel did not hamper lamprey or the other species. Greater water flow, and thereby greater immersion depth on the ramp fostered passage for all species. Smaller-bodied individual of creek chubs and white suckers performed best on the ramp. We show that wetted ramps could be incorporated into fishways at low-head dams to aid passage of smaller-bodied fishes while also blocking the spawning migration of adult sea lamprey.