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. C") (.-:1 .~. t'-' .. , ".. ,..... 00 While other non-native species are common and widespread in the San Juan River, channel catfish are of the greatest concern due to their widespread distribution and high abundance patterns (Sublette et aL1990) and documented predation on native fish communities (Marsh and Brooks 1989, Tyus and Nikirk 1990, Marsh and Douglas 1997), The earliest report of channel catfish in the San Juan basin was 1957 (University of New Mexico, Museum of Southwestern Biology collection), but it is likely the species arrived prior to that date. The establishment of channel catfish in the basin was the result of concerted stocking efforts by state and federal agencies (NMDFG and USFWS files). Although apparently well established, irregular stocking of channel catfish in lotic environments of the San Juan River sub-basin continued into the 1980's, While the New Mexico Department of Game and Fish ceased stocking the species in the river in the early 1980's, it is still stocked in impoundments in the drainage (NMDGF files). There are no official records of its being stocked in the riverine portions of the basin in Utah, at least in the past 30 years (UDWR files). In Colorado, few riverine habitats are suitable for the species, but it does occur in several reservoirs where it continues to be stocked (CDOW files). Other non-native fish species in the San Juan River, particularly the ubiquitous common carp, likely also play an important role in the restoration and management of the native fish community. Common carp were first introduced into North America in 1831, and in 1879, the U.S, Fish Commission began a stocking program in an effort to address depleted inland fisheries. It is not known when common carp were originally introduced into the San Juan River sub-basin, but Sublette et al. (1990) reported that this species was first introduced into New Mexico waters in 1883. Evermann and Rutter (1895) reported the presence of common carp in the Colorado River Basin during the late 1800's, and it is probable that this species has been in the San Juan River since the turn of the century. The vast reproductive potential and generalist life history patterns for common carp (Panek 1987) imply that this species may be a significant competitor with native fishes for aquatic resources. Minckley (1973) wrote: The effects of carp on other fishes are subtle. They are remarkably adaptable animals, wilh broad spectra of tolerances to chemical conditions, lemperatures, currents, foods, and spawning condition, and therefore probably influence most species (directly or indirectly) with which they OCcur. With the closure of Glen Canyon Dam on the Colorado River in early 1963, the formation of Lake Powell and associated establishment of lacustrine, non-native piscivore populations began. The periodic occurrence oflargemouth bass, striped bass, and walleye in upstream reaches of the San Juan River may increase predation pressure on native species, Largemouth bass and walleye were first collected from the Colorado River reach currently inundated by Lake Powell in 1962, prior to completion of Glen Canyon Dam (Stone and Miller 1966), Striped bass fingerlings were introduced into Lake Powell on an annual basis 1974-1979. Successful reproductive efforts have been documented since, and they maintain a large reservoir population (Gustaveson et at 1984). Ryden and Pfeifer (1996) have reported on sporadic occurrences of these species in the San Juan River upstreanl of Lake Powell. While relatively uncommon, these species are all highly piscivorous (Carlander 1950, Minckley 1973, Sublette et at 1990) and may influence resident native populations, particularly in the lower San Juan River. San Juan River Non-native Species Interactions, Final Report, I February 2000 3