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c) c;-, .... co .....J 1'0 . . Walleye were collected as far upstream as RM 108.3 and striped bass as far upstream as RM 91.2. The upstream limit of threadfin shad distribution appears to be Government Rapid at RM 20.2. Both flannelmouth sucker and bluehead sucker showed declining CPOE between 1991 and 1997 in the core sampling area (RM 158.6-53.0). Oeclines in flannelmouth sucker CPOE were much more dramatic than those for bluehead sucker. However, during the same time period, the average condition factor of these two fish species increased. In addition, CPUE for both of these species increased in Reach 6 (RM 180.0-158.6) collections. The declines in flannelmouth sucker and bluehead sucker populations may be cyclical fluctuations in these populations. There does not appear to be a resident, reproducing population of roundtail chub in the San Juan River. The individual roundtail chub collected in the san Juan River during the seven-year research period appear to be originating from upstream tributaries, namely the Animas, La Plata, and Mancos River drainages, that support populations of roundtail chub. Between 1991 and 1993, no wild razorback sucker were collected in the San Juan River. Razorback sucker that were experimentally-stocked between 1994 and 1997 appear to be surviving and growing in the San Juan River. Adult monitoring has also proven to be efficient in monitoring juvenile Colorado pikeminnow that were experimentally-stocked by the Utah Division of Wildlife Resources in 1996 and 1997. Thirty-nine of these fish ranging from 44-235 rom total length (TL) were recaptured in 1997. Thirty-eight of these recaptured juvenile Colorado pikeminnow were in the 125-235 mm TL range. Six of which were implanted with PIT tags. The sampling regime presently in place for adult monitoring studies appears to be efficient for monitoring stocked juvenile Colorado pikeminnow greater than 100 mm TL. Between 1991 and 1995, 19 wild Colorado pikeminnow, 17 adults (519-945 mm TL) and two large juveniles (363 and 432 mm TL) were collected via electrofishing. All of these Colorado pikeminnow were captured downstream of CUdei Oiversion (RM 142.0). Of the 19 COlorado pikeminnow collected, 16 (all adults) were collected in the section of the San Juan River between CUdei Diversion and the Four Corner's bridge (RM 142.0-199.2). Thirteen wild, adult Colorado pikeminnow were implanted (tagged) with radio transmitters (tags). All 16 Colorado pikeminnow captured and tagged between RM 142.0 and 119.2 remained in a 33-mile section of river from RM 142.0-109.0. This area of the San Juan River seems to have properties that make it a "preferred" reach for adult COlorado pikeminnow. Adult COlorado pikeminnow appear to have very small home ranges which they occupy throughout most of the year, moving only during pre-spawning (mid-May through June) and spawning (July through mid- August) periods. Only one adult Colorado pikeminnow demonstrated migratory behavior. This individual, a large female fish, moved upstream from her home range downstream of "Bluff, Utah apparently to spawn in the summer of 1994. Of the 13 radio-tagged Colorado pikeminnow, 11 were contacted in area of the San Juan River known as the Mixer (RM 133.4-129.8) during presumed spawning periods. Seven individual adult Colorado pikeminnow were contacted in or at the mouth of the Mancos River (RM 122.6) during pre-spawn periods, a behavior dubbed "staging." Two fish tracked in multiple years used the Mancos during two separate pre-spawn periods. Two fish tracked in multiple years, inCluding one of the fish contacted in the Mancos in two separate years moved to the Mixer during two separate spawning seasons. There appears to be a seasonally-repeated behavior among San Juan River Colorado pikeminnow of staging at the Mancos River, then moving to the Mixer to spawn. . I . i " I . i . i . I iii i ~ i ~