WSP06287 - Laserfiche WebLink

Home Browse Search

-, EXECUTIVE SUMMARY The San Juan River is historic habitat for seven native fish species including three rare fish species: the Colorado squawfish (Ptvchocheilus lucius), razorback sucker (Xvrauchen texanus), and roundtail chub (Gila robusta). In 1993, the U.S. Fish and Wildlife Service's Colorado River Fishery Project (CRFP) office in Grand Junction, Colorado, in cooperation with other state and federal agencies, conducted electrofishing surveys on the lower mainstem San Juan River. The primary responsibility of the CRFP office is to monitor the juvenile and adult fish community in the river's main channel habitat. The river was electrofished from river mile (RM) 179.0 (Farmington, New Mexico; Reach I) to RM 2.9 (Clay Hills Boat Landing; Reach VII), during two sampling trips. All seven river reaches were sampled once each during 1993. In addition, two Colorado squawfish "hunts. were conducted in April and May. The purpose of these trips was to implant radio tags into adult Colorado squawfish for another study. The most abundant species collected was flannelmouth sucker (Catostomus latioinnis), followed in descending order by bluehead sucker (Catostomus discobolus), channel catfish (Ictalurus ounctatus), and common carp (Cvorinus caroio). Fish community composition did not change drastically from 1991-1992, however some differences were noted in 1993. Catch rates for all species were down riverwide from 1992. Common carp and channel catfish accounted for only 15% of the total catch in 1993, lower than in previous years. All other introduced species accounted for only 3% of the total catch. Among these was the first recorded capture of a grass carp (Ctenooharvnqodon idella), near Aneth, Utah. Native species, mostly flannelmouth sucker and bluehead sucker, composed B2% of the total catch in 1993, up from previous years. Colorado squawfish and roundtail chub combined again composed less than 1% of the total catch. Electrofishing capture rates were highest for flannelmouth sucker and bluehead sucker in Reach III (Shiprock, New Mexico to Four Corners Bridge), while catch rates for speckled dace (Rhinichthvs osculus) were highest in Reach II (Hogback Diversion, New Mexico to Shiprock). The three most abundant nonnative species--channel catfish, common carp, and red shiner--had their highest catch rates in Reaches IV (Four Corners Bridge to Aneth, Utah), II, and VII (Mexican Hat, Utah to Clay Hills Boat Landing, Utah), respectively. Catch rates for most species showed a downward trend as sampling proceeded downriver from Hogback Diversion. Examination of the population size structure of the four most abundant species captured over the last three years revealed that both flannelmouth sucker and channel catfish populations showed distinct shifts from larger to smaller fish in downriver reaches. Common carp had more juvenile fish in their population in 1993 than in 1991 and 1992. Five Colorado squawfish and two roundtail chub were collected in 1993. Only one of the Colorado squawfish was collected during a standardized adult monitoring trip, all others were collected during special Colorado squawfish "hunt" trips. No razorback sucker were collected. Four of five Colorado squawfish were captured in Reach II', as were both roundtail chub. The fifth Colorado squawfish was captured in Reach VI (Bluff to Mexican Hat, Utah). This is the most downstream capture of an adult Colorado squawfish in the mainstem San Juan River. All five Colorado squawfish were surgically implanted with radio tags and tracked year-round from the air and ground. Fifty-one radio contacts were made with these fish between January and December 1993. For the third year in a row radio-tagged Colorado squawfish demonstrated an affinity for the area in I' "