Bureau of Reclamation - Lower Colorado Region

Description

Razorback sucker (Xyrauchen texanus) were once abundant and broadly distributed throughout the Colorado River basin. Water development and introduction and establishment of non-native species resulted in widespread extirpation and declines in distribution and abundance of these and other native species. The razorbacks immediately benefitted from the large newly created impoundments as its populations increased considerably in the years following dam closures. Unfortunately, these and other populations failed to recruit, resulting in dramatic reductions in the number and size of populations as adult fish aged and died, ultimately leading to its listing as endangered (U.S. Fish and Wildlife Service 1991). Razorbacks exhibit high levels of genetic variation that persist, especially in the largest remaining population of Lake Mohave (Dowling et al. 1996b, 2005, 2007). Given this combination of population size and high levels of genetic diversity, the lower river has been a focal point for management action for this species. Early efforts focused on stocking large numbers of hatchery-reared individuals; however, this approach has met with limited success (Marsh et al. 2003, 2005; Schooley and Marsh 2007; Schooley et al. 2008). Most early stockings were of small fish that apparently were lost to predation. A separate repatriation program for restoring razorback sucker in Lake Mohave was begun in the early 1990s (reviewed in Minckley et al. 2003), and perpetuation of that population now is dependent on a long term repatriation program. The Lake Mohave program utilizes wild-produced larvae that are reared in protective custody and repatriated to the lake with the ultimate goal of replacing the pre-existing wild population. This repatriation program was incorporated into the Multi-Species Conservation Program (MSCP) which annually collects wild produced larval fish to be reared for its fish augmentation program. The MSCP currently stocks in excess of 18,000 (300mm plus) razorbacks a year throughout the lower Colorado River (LCR). Long-term survival has been disappointing even for many of the larger fish stocked in recent years (Schooley et al. 2004, 2008). Despite poor long-term survival of stocked fish and general absence of recruitment, collections of larvae have been made in the reach below Davis Dam, in Lake Havasu, and at several localities in the reach downstream from Blythe, California. As in Lake Mohave, these larvae persist only a short time post-swim-up before succumbing to predation or some other cause of mortality. The number and identity of parents contributing to this production are unknown. Unlike Lake Mohave and the LCR, the situation seems more promising in Lake Mead as limited success in razorback reproduction and apparent recruitment has been obtained (Albrecht et al. 2008). Several projects have been initiated to identify specific features of Lake Mead that would allow razorbacks to successfully recruit.

Who can apply

• Others

Contact

Shawna Thompson <br/>Grant Officer <br/>Phone 702-293-8570
smthompson@usbr.gov