C150094 Addendum to Biological Assesment for Long Hollow

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Addendum to Biological Assessment for the Proposed Long Hollow Reservoir Natural reproduction of Colorado pikeminnow has been documented from the San Juan River since monitoring was initiated in 1987, however, it has been less frequent in the last few years. The number of wild Colorado pikeminnow in the San Juan River sub basin is considerably lower than in the Upper Colorado River or Green River sub basins; only 17 wild adults and 2 juveniles were captured in the entire San Juan River between 1991 and 1995. Fifteen sampling trips were conducted between June 1991 and October 1995 (three trips per calendar year) from river miles (RM) 136.6 (Stump Camp) to RM 119.2 (Four Corner's Bridge). This 17.4-mile reach was the only common section of the San Juan River sampled during all 15 trips, and only 15 adult Colorado pikeminnow were captured in this reach. Radiotelemetry confirmed that these 15 fish were year-round residents of this river section. Of the 15 fish captured, 9 were recaptured (3 were recaptured twice). A Schnabel multiple-census population estimate for fish captured and recaptured between 1991 and 1995 yielded an estimate of 19 adult fish (95 percent confidence intervals = 10-42). It is estimated that there were probably fewer than 40 wild adult Colorado pikeminnow in the entire San Juan River as of October 1995 (Personal Communication, Dale Ryden, U.S. Fish and Wildlife Service). Only three wild Colorado pikeminnow were captured in the San Juan River between 1995 and 2001; 2 juveniles (363 and 432 mm TL) near Lake Powell in 1996; 1 adult originally captured in April 1993, recaptured in 1998, 1999, and 2000 (all from RM 136.6- 119.2). Radio-telemetry studies indicate that the fish were able to ascend the Cudei Diversion, but present upstream extension of wild fish in the San Juan River is to the PNM weir, which diverts water to the Four Corners power plant at River Mile (RM 163.3) (Ryden and Pfeifer 1995; Ryden 2000a). Recently a non-selective fish passageway has been completed at the Hogback Diver (RM 158.6) and a selective fish passageway will be completed at the PNM weir within 2003. Fifty adult Colorado pikeminnow were stocked in the San Juan River in October 1997. Fifteen of these fish were implanted with radio-transmitters and monitored for habitat use through 1998; the fish showed little movement from areas of release. Drift studies showed that young Colorado pikeminnow are found only in the lower river reaches and the high water zone of Lake Powell. 991-077.080 Wright Water Engineers, Inc. Page 3 November 2003