Swimming Performance of Juvenile Paddlefish: Quantifying Risk of Entrainment
Jan Jeffrey Hoover, April Turnage, and K. Jack Killgore
Abstract.—Rheotaxis, endurance, and behavior of juvenile paddlefish Polyodon spathula (<115 mm eye-to-fork length) were measured in a laboratory swim tunnel. Paddlefish were positively rheotactic (>80% of individuals tested). They exhibited sustained swimming ($200 min) at water velocities up to 40 cm/s, prolonged swimming (0.5–52 min) at 30–50 cm/s, and burst swimming (<0.5 min) at water velocities 60–75 cm/s. Behavior consisted exclusively of free swimming in the water column. Fish recovered from white spot Ichthyophthirius multifiliis disease appeared healthy but had reduced endurance at low to moderate water velocities. Data were used to quantify risk of entrainment by dredges at a given water velocity as an index, values of which ranged from 0.00 (unlikely) to 1.00 (inevitable). Entrainment risk was evaluated for escape speeds considered environmentally conservative (based on prolonged swim speed) and operationally conservative (based on burst swim speed), using flow field models of three cutterhead dredges having pipe diameters of 71, 51, and 30 cm. Entrainment was likely within a radius of 1.25 m of the cutterhead, but degree of risk and distance of entraining flow varied substantially with pipe size. Entrainment risk of paddlefish can be reduced by (1) temporal restrictions on dredging, (2) stocking juveniles that have not been treated for disease, and (3) use of small diameter pipes (ideally < 30 cm).