Spatial and Temporal Use of a Spawning Site in the Middle Green River by Wild and Hatchery-Reared Razorback Suckers

Abstract

The population of endangered razorback suckers Xyrauchen texanus in the middle Green River (upper Colorado River basin) has declined during the last 40 years. The apparent cause for this decline is a lack of successful recruitment. This study used radiotelemetry to evaluate the ability of hatchery-reared razorback suckers to locate spawning areas where wild fish congregate during the ascending hydrographic limb of the snowmelt runoff. Hatchery-reared razorback suckers appeared to show similar reproductive behavior to wild fish. Both wild and hatchery-reared fish were found near the middle Green River spawning area between 1 and 25 May 2000. Hatchery fish occupied the same areas on the spawning site as wild fish, and remained on the spawning site during both nocturnal and diurnal hours. Males were more abundant on the spawning area than females, but the few females captured tended to stage away from the primary spawning area. The results from this study suggest hatchery-reared fish are capable of responding to natural cues that prompt spawning aggregations and are successful in locating existing spawning aggregations of wild fish. Given attention to stocking criteria, including genetic diversity and the size and time of stocking, the challenges of recovering razorback suckers will center on those factors that led to the population declines, particularly the survival of early life stages in off-channel habitats.