Mechanical removal of nonnative fishes as a management tool for the recovery of Colorado pikeminnow, Ptychocheilus lucius, and razorback sucker, Xyrauchen texanus, in the San Juan River - New Mexico, Colorado and Utah.

Authors: Bobby Ray Duran, Jason E. Davis, Weston Furr, Ernest Teller

Year: 2009 (xli)

Abstract

The San Juan River, New Mexico, Colorado and Utah, is home to two federally endangered fishes, Colorado pikeminnow, Ptychocheilus lucius, and razorback sucker, Xyrauchen texanus. It is widely accepted that altered flow regimes, habitat degradation and fragmentation, and the introduction and establishment of nonnative fishes contributed to the decline of these fishes. The San Juan River Basin Recovery Implementation Program’s (SJRIP) Long Range Plan has identified nonnative fish control as a management element for recovery efforts. Beginning in 2001, intensive mechanical removal via raft mounted electrofishing was initiated in discrete river reaches. Efforts focused on the removal of all nonnative fishes with emphasis on channel catfish, Ictalurus punctatus, and common carp, Cyprinus carpio. In 2008, a total of 16,968 channel catfish and 1,173 common carp were removed from river miles (RM) 166.6 - 52.9 in 769.63 hours of electrofishing. The lowest channel catfish catch rates (fish/hour of electrofishing; CPUE) since the initiation of intensive nonnative fish removal were observed in each of the two upper sections (PNM Weir to Hogback Diversion, RM 166.6 - 159.0; Hogback Diversion to Shiprock Bridge, RM 158.6 - 147.8). Channel catfish catch rates from PNM Weir to Hogback Diversion in 2008 were similar to CPUE in 2007 but were significantly (p<0.05) lower than values observed from 2001-2005. Similar to the adjacent upstream reach, channel catfish CPUE from Hogback Diversion to Shiprock Bridge was similar to CPUE in 2007 but was significantly (p<0.05) lower than values observed from 2003-2006. Significant (p<0.05) declines in common carp CPUE was observed during the study period and collections of common carp have become infrequent riverwide. Measurable channel catfish recruitment in upper sections of the San Juan River has not been documented since 2002. These data suggest that reduced abundance of adult fish via mechanical removal has been successful in reducing the overall reproductive output and subsequent recruitment of channel catfish. Although complete eradication of these species is unexpected, utilizing multiple pass electrofishing has and is expected to continue to reduce abundance to manageable levels. By reducing abundance and biomass of nonnative fishes, negative spatial and trophic interactions with common and rare native fishes may be reduced.