Assessing the risk of entrainment by cutterhead dredges to juvenile lake sturgeon (Acipenser fulvescens) and juvenile pallid sturgeon (Scaphirhynchus albus)

Abstract

Summary Sturgeon are threatened by dredging, but there is no established protocol for determining risk of entrainment to different populations of wide-ranging species. We demonstrate that laboratory evaluations of swimming performance for individual populations are an effective way to describe susceptibility of entrainment. Using a Blazka-type swim tunnel, we quantified positive rheotaxis (head-first orientation into flowing water), endurance (time to fatigue), and behaviour (method of movement) of juvenile sturgeon in water velocities ranging from 10 to 90 cm s−1. Sturgeon representing four different populations of the United States were tested: two populations of lake sturgeon (Acipenser fulvescens) and two populations of pallid sturgeon (Scaphirhynchus albus). Lake sturgeon from Lake Winnebago were weaker swimmers than those from the Wisconsin River, and pallid sturgeon from the Yellowstone River were weaker swimmers than those from the Atchafalaya River. Rheotaxis, endurance, and behavioural data were used to calculate an index of entrainment risk, ranging from 0 (unlikely) to 1.00 (inevitable), which was applied to hydraulic models of dredge flow fields. Risk of entrainment varied among populations but for all groups tested, substantial entrainment risk occurred only within a 1.25 m radius of the draghead and this risk could be significantly reduced or eliminated by reducing the diameter of the dredge pipe.