9508 - Laserfiche WebLink

Home Browse Search

Over 40 species of nonnative fish have become established in the Upper Colorado River Basin (Tyus et al. 1982). Many of these species are predators and competitors of native fishes, and nonnative species are considered a principal cause in species endangerment. One of seven Recovery Program elements is Reduction of Nonnative Fish and Sportfishing Impacts, and activities in the upper basin have been implemented and are ongoing to reduce the detrimental effects of these nonnatives. Floodplains attract large numbers of nonnative fishes and some of these species reproduce in these habitats (Modde 1997; Birchell and Christopherson 2002; Burdick 2002; Mueller 2003). The principal and most common floodplain species include a variety of cyprinids, centrarchids, and ictalurids. Nonnative fish control efforts in the upper basin have yielded variable results, and show that certain large predators (i.e., northern pike [Esox lucius], smallmouth bass [Micropterus dolomieui], channel catfish [Ictalurus punctatus]) can be reduced in numbers, but small forms (e.g., red shiner, fathead minnow, green sunfish, bullheads) are less affected (Upper Colorado River Endangered Fish Recovery Program 2002). The large numbers of nonnative fishes in floodplains can be logistically difficult to control without intensive long-term management and substantial ongoing financial investment , which are not consistent with the concept of population self-sustainability for recovered species. This highly-managed approach (i.e., "floodplain repatriation") of isolation of floodplains from the river channel and mechanical or chemical removal of nonnative fishes is being used in the Lower Colorado River Basin where flows are highly regulated and habitat is extensively fragmented (Minckley et al. 2003; Mueller and Marsh 2003). 3.0 Scientific Basis And Underlying Principles 3.6 Nonnative Fish In Floodplains 3-9 April 2004 Principal nonnative fishes in floodplains . Common carp (Cyprinus carpio), Fathead minnow (Pimephales promelas), Green sunfish (Lepomis cyanellus), Black bullhead (Ameiurus melas), Red shiner (Cyprinella lutrensis), and Largemouth bass (Micropterus salmoides) . . . . . The strategy of floodplain management recommended for the upper basin is based on the "reset theory", and is different from the "floodplain repatriation" approach. Resetting floodplains allows periodic inundation and desiccation that provide timely productive habitats for native fishes and reduce numbers of nonnative forms (see section 3.7). Spring flooding allows entrainment of drifting razorback sucker larvae, escapement of older fish, and periodic desiccation serves to reset the floodplain and kill all remaining fish. Nonnative fishes can also access the floodplains during connection with the river, but initially in low numbers and primarily as adults which generally feed on prey larger than larvae. Reproduction by nonnatives occurs in late spring and summer when size of young razorback sucker exceeds that of newly- produced nonnatives, hence reducing predation effects.