Larval Razaorbakc Sucker and Bonytail Survival and Growth in the Presence of Nonnative Fish in the Baeser Floodplain Wetland of the Middle Green River

摘要

Floodplain restoration is an important element of the Upper Colorado River Endangered Fish Recovery Program. Floodplain restoration was initiated in 1996 by lowering natural and manmade levees that were preventing natural floodplain function by limiting the frequency and duration of river-floodplain connection. Floodplain wetlands provide important rearing habitat for endangered razorback sucker (Xyrauchen texanus) and bonytail (Gila elegans) larvae. Nonnative fish species such as fathead minnow (Pimephales promelas), black bullhead (Ameiurus melas), green sunfish (Lepomis cyanellus), and carp (Cyprinus carpio) flourish in this type of habitat and likely suppress survival of less abundant endangered fish species. Drought conditions eliminate, or reset, fish populations in wetlands that result in much lower initial fish densities during the next inundation period. Survival of larval razorback sucker and bonytail following reset of a floodplain wetland has been documented. The goal of this study was to estimate the lower density threshold at which survival of larval razorback sucker and bonytail could be detected. Survival was evaluated at different levels of larval razorback sucker density and one level of bonytail density. Using twelve 1/8-acre experimental enclosures, equal numbers of nonnative fish species were introduced into ten of the twelve enclosures. The remaining two enclosures were established as controls (no nonnative fish). Growth of surviving razorback sucker and bonytail was also evaluated.