2022-12-19_GENERAL DOCUMENTS - C1981010

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Monitoring for adult Colorado pikeminnow currently occurs every year on the San Juan River. hi 2013, 149 Colorado pikeminnow were collected during monitoring from RM 180-77, the eighth consecutive year that more than 100 Colorado pikeminnow were caught in this reach (Schleicher 2014). However, only 7 of these fish were greater than 450 mm (18 in). In addition, 19 Colorado pikeminnow greater than 450 mm (18 in)were collected during the non-native fish removal trips in 2013 (Duran et al. 2014). In order to downlist the species,the San Juan River population of Colorado pikeminnow must reach at least 1,000 Age-5 fish (Service 2002). The majority of individuals come from hatchery reared stocks supported by the San Juan River Recovery Implementation Program. This program has stocked more than 2 million age 0 and age 1+fish in the San Juan River since 2002 (Fury and Davis 2009). River wide population estimates for age-2+pikeminnow that have been in the San Juan River at least one year was approximately 4,600 and 5,400 individuals in 2009 and 2010,respectively(Duran et al. 2010; 2013). However,because few adult Colorado pikeminnow were detected in the San Juan River, this population estimate largely consists of juveniles. Other Colorado pikeminnow abundance estimates exhibit substantial annual variation, likely due to the effects of short-term retention from recent stocking events,but no clear population trends were evident in the San Juan River Basin (Durst 2014). Successful Colorado pikeminnow reproduction was documented in the San Juan River in 1993, 1995, 1996, 2001, 2004, 2007, 2009-2011, and 2013. A total of 58 larval Colorado pikeminnow were collected since 1993 (Farrington and Brandenburg 2014); however, there has been little to no recruitment documented in the San Juan River. A total of 48 Age-1+ Colorado pikeminnow were collected in 2013; all presumably the result of augmentation efforts (Farrington and Brandenburg 2014). Since 1998, Colorado pikeminnow were collected during small-bodied monitoring every year except 2001-2003; however,young of year(YOY) Colorado pikeminnow were stocked in each of these years prior to monitoring efforts so these fish were likely hatchery-reared (Service 2015b). Larval Colorado pikeminnow detections occurred throughout the San Juan River from Reach 4 (RM 106-130) downstream to Reach 1 (RM 0-16) (Farrington and Brandenburg 2014, Service 2015b). Franssen et al. (2007) found that maintenance of a natural flow regime favored native fish reproduction and provided prey at the appropriate time for Age-1 Colorado pikeminnow. Tissue samples from Colorado pikeminnow caught during research conducted under the Recovery Program have been analyzed as part of a basin-wide analysis of endangered fish genetics. The results of that analysis indicate that the San Juan River fish exhibit less genetic variability than the Green River and Colorado River populations, likely due to the small population size,but they were very similar genetically to pikeminnow from the Green, Colorado, and Yampa rivers (Morizot in lift. 1996). These data suggest that the San Juan population is probably not a separate genetic stock(Holden and Masslich 1997; Houston et al. 2010). To summarize, the Colorado pikeminnow was quite rare in the San Juan River in the 1990s,with an estimate of less than 50 adults. Since 2002, millions of young Colorado pikeminnow have been stocked into the river. Adult fish are still rather uncommon, however, and not nearly at the level yet needed for recovery. Despite low numbers of adults,reproduction is occurring to some extent, but recruitment is low. Most of the Colorado pikeminnow in the San Juan River are 13