US Fish & Wildlife Service


Date of this Version



Published by the U.S. Fish and Wildlife Service, 1-129, (2000)


As part of the San Juan River Basin Recovery Implementation Program (SJRIP), investigations of non-native fishes were conducted during 1991-1997 to characterize interactions with native fishes. The impacts of non-native fish species on natives has often been identified as a key impact, along with habitat alteration, that facilitates loss of native biological diversity. In the San Juan River, the endangered Colorado pikeminnow Ptychocheilus lucius and razorback sucker Xyrauchen texanus, as well as the other members of the native fish community, are the focus of the SJRIP. A major component of native fish recovery efforts in the San Juan River is the mimicry of the natural hydrograph, and SJRIP studies were designed to assess the response of the resident fish community to variable flow conditions affected the releases from upstream Navajo Dam. Section 5.4 of the SJRIP Long Range Plan identified several informational and action needs regarding non-native fish species: 1) characterize distribution and abundance patters of non-native fishes, 2) characterize habitats used by non-native fishes, 3) describe the food habits of non-native fishes, 4) characterize the response of non-native fishes to varying flow regimes, 5) develop a non-native fish stocking policy, 6) develop regulations to restrict bait-fish species harvest, 7) develop regulations to control importation of non-native fishes, and 8) monitor and evaluate non-native fishes control actions implemented as part of the SJRIP. This report presents results of non-native fishes investigations that address items 1-4 and 8 above.

The distribution and abundance patterns of large-bodied non-native fishes were studied to determine responses to varying flow regimes. Sampling was primarily by raft-mounted electrofishing, but also included limited hoop and trammel netting. Main and secondary channel sampling collected 18 species of non-native fish. Channel catfish Ictalurus punctatus and common carp Cyprinus carpio were the most abundant and the most widely distributed species. Seasonal movements of striped bass Morone saxatilis and walleye Stizostedion vitreum out of Lake Powell and upstream into the San Juan River as far as Shiprock, New Mexico were documented. Mark and recapture studies of channel catfish and common carp were used to estimate abundance and to evaluate movement patterns for the entire reach of the San Juan River sampled, Farmington, New Mexico downstream to Clay Hills, Utah. Schnabel population estimates (95% C.I.) for channel catfish ranged from 131,768 (72,143 - 219,393) in 1992 to 274,484 (115,712 - 563,162) in 1995 and for common carp were 26,576 (14,213 - 45,019) in 1992 to 107,268 (61,438 - 172,692) in 1995. The proportional abundance of non-native species sampled during electrofishing surveys in main and secondary channel habitats increased during 1994-1997, after initial declines observed during1991-1994. Implementation of high spring releases from Navajo Dam did not appear to negatively impact non-native species distribution or abundance.