Factors Influencing Poststocking Dispersal of Razorback Sucker

Efforts to reintroduce razorback suckers Xyrauchen texanus to specific river reaches have been plagued by downstream drift and poor survival, which have been attributed to stress, disorientation, predation, and poor conditioning. Poststocking dispersal of eight test groups (15 fish each) of razorback suckers was examined for 28 d with telemetry equipment. Fish were released in three different locations in the Colorado River basin of Utah, Arizona, and Nevada: (1) a 65,000-ha reservoir, (2) a small (<1-ha) backwater, and (3) a large (30-ha) backwater on the mainstem river. At each location, subgroups were released immediately (reference) or held to acclimate them to the site (3-7 d) before release. Two of four subgroups for the large-backwater test were preconditioned to flow. Dispersal from the stocking sites was rapid and declined with time for all tests, as fish appeared to seek and find cover. Downstream drift was most pronounced (<(x)over bar> = 69.5 km) from the small backwater and significantly (Kruskal-Wallis test, P < 0.01) greater than either the reservoir (<(x)over bar> = 3.7 km) or large-backwater sites ((x) over bar = 7.7 km). Site-acclimation tests were inconclusive, but downstream movement was significantly (Wilcoxon two-sample test, Z = -2.298, P < 0.01) less for fish preconditioned to flow (<(x)over bar> = 1.9 km) compared with pond-reared fish ((x) over bar = 7.7 km). We concluded that poststocking dispersal may decrease if razorback suckers are preconditioned to flow.