Razorback sucker recruitment in Lake Mead, Nevada–Arizona, why here?

Abstract

Populations of the endangered razorback sucker (Xyrauchen texanus) have been reduced in the Colorado River during much of the last century. The inability of razorback sucker to recruit in the presence of nonnative fishes and altered flow regimes is thought to be the major factor contributing to their decline. Through funding from the Southern Nevada Water Authority and the US Bureau of Reclamation, we have conducted an ongoing razorback sucker research project on Lake Mead, Arizona and Nevada, since 1996. A major emphasis of this research has been to determine if natural recruitment was occurring in Lake Mead and identify reasons for that recruitment. Ages calculated using a nonlethal aging technique for 186 individual razorback sucker indicate the Lake Mead population is relatively young and that natural, wild recruitment has regularly occurred since the late 1970s. Comparisons of back-calculated ages of captured fish with historical Lake Mead water elevations provide evidence that a change in annual lake level fluctuations is the most likely mechanism that initiated this recruitment phenomenon. Lake level changes along with inundated terrestrial vegetation and turbidity in specific sites in Lake Mead may provide littoral nursery cover for larval and juvenile razorback sucker, allowing them to avoid predation.