Laserfiche WebLink
EXECUTIVE SUMMARY <br />Floodplain restoration is an important element of the Upper Colorado River <br />Endangered Fish Recovery Program. Floodplain restoration was initiated in 1996 by <br />lowering natural and manmade levees that were preventing natural floodplain function by <br />limiting the frequency and duration of river-floodplain connection. <br />Floodplain wetlands provide important rearing habitat for endangered razorback <br />sucker (Xyrauchen texanus) and bonytail (Gila elegans) larvae. Nonnative fish species <br />such as fathead minnow (Pimephales promelas), black bullhead (Ameiurus melas), green <br />sunfish (Lepomis cyanellus), and carp (Cyprinus carpio) flourish in this type of habitat <br />and likely suppress survival of less abundant endangered fish species. Drought <br />conditions eliminate, or reset, fish populations in wetlands that result in much lower <br />initial fish densities during the next inundation period. Survival of larval razorback <br />sucker and bonytail following reset of a floodplain wetland has been documented. <br />The goal of this study was to estimate the lower density threshold at which <br />survival of larval razorback sucker and bonytail could be detected. Survival was <br />evaluated at different levels of larval razorback sucker density and one level of bonytail <br />density. Using twelve 1/8-acre experimental enclosures, equal numbers of nonnative fish <br />species were introduced into ten of the twelve enclosures. The remaining two enclosures <br />were established as controls (no nonnative fish). Growth of surviving razorback sucker <br />and bonytail was also evaluated. Survival of razorback sucker larvae was detected in two <br />enclosures stocked at the highest density of 40,000 larvae/acre (2 and 3%) and at the <br />lowest density of 400 larvae/acre (6 - 23%). Bonytail stocked at a density of 8,000 <br />viii <br />