2010-11-22_REVISION - M2009023 (7)

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Population Dvnamics Due to the low numbers of Colorado pikeminnow collected in the San Juan River, it is not possible to quantify population size or trends. However, estimates during a seven-year research period between 1991 and 1997 suggest that there were less than 50 adults in a given year (Ryden 2000a). The ability of the Colorado pikeminnow as a species to withstand adverse impacts to its populations and its habitat is difficult to discern given the longevity of individuals and their scarcity within the San Juan River basin. At this stage of the investigations on the San Juan River, the younger life stages of the species is considered the most vulnerable to predation, competition, and habitat degradation through contamination. Population level response times to rebound from these impacts may take several years or more. Tissue samples from Colorado pikeminnow caught during research conducted under the Program have been analyzed as part of a basin-wide analysis of endangered fish genetics. The results of that analysis indicated that the San Juan River fish exhibited less genetic variability than the Green River and Colorado River populations, likely due to the small population size in the San Juan (Morizot in litt. 1996), but were very similar to Colorado pikeminnow from the Green, Colorado, and Yampa rivers, suggesting that the San Juan population is probably not a separate stock (Holden and Masslich 1997). Analysis of Species&ritical H#bitat Likely to be Affected The San Juan River currently flows approximately 225 river miles from the Navajo Dam downstream to Lake Powell. Of the 225 miles, 166.6 miles are currently available to the Colorado pikeminnow. Ryden and Pfeifer (1993) identified five diversion structures between Farmington, New Mexico, and the Utah state line that potentially acted as barriers to fish passage at certain flows (Cudei, Hogback, Four Comers Power Plant, San Juan Generating Station, and Fruitland Irrigation Canal diversions). When radio telemetry studies were initiated on the San Juan River in 1991, only one radio-tagged pikeminnow was recorded moving upstream past one of the diversions. In 1995, an adult pikeminnow moved above the Cudei Diversion and then returned back downstream (Miller and Ptacek 2000). Other native fish had been found to move either upstream or downstream over all five of the weirs (Bunt er and Brooks 1997, Ryden 2000a). In 2001, Cudei Diversion (RM 142) was removed from the river and Hogback Diversion (previously an earth and gravel berm structure), which had to be rebuilt every year, was made into a permanent structure with non-selective fish passage. Channel catfish that were tagged downstream of the Hogback Diversion in spring and summer 2002 were recaptured upstream of the structure in summer and fall, 2002 (Davis, USFWS, pers. comm., 2002). It is highly likely that pikeminnow, razorback sucker, and other native:fishes can negotiate the ladder. The removal of Cudei Diversion and installation of the fish ladder at Hogback Diversion improved access for native fishes over a 24.5 mile reach of river. Until 2003, the PNM weir (RM 166) was also a barrier to fish passage. With the completion of the PNM selective fish ladder in 2003, passage is now possible past that structure. Between June and December 2003, 17,394 native fish used the passage including 9 pikeminnow and 4 razorback suckers (Albert LaPahie, Navajo Fish and Wildlife, unpublished report 2003).