WSP09475

• File Number: 8240.300.10
• Description: San Juan Endangered Fish Recovery Program
• Basin: San Juan/Dolores
• Date: 1/1/2000
• Author: USDOI/FWS
• Title: Adult Fish Community Monitoring on the San Juan River 1991 - 1997
• Water Supply Pro - Doc Type: Publication

Walleye were collected as far upstream as RK 108.3 and striped bass as far
upstream as RK 91.2. The upstream limit of threadfin shad distribution
appears to be Government Rapid at RK 20.2.
Both flannelmouth sucker and bluehead sucker showed declining CPUE
between 1991 and 1997 in the core sampling area (RK 158.6-53.0). Declines in
flannelmouth sucker CPUE were much more dramatic than those for bluehead
eucker. However, during the same time period, the average condition factor of
these two fish epecies increased. In addition, CPUE for both of these species
increased in Reach 6 (RK 180.0-158.6) collections. The declines in
flannelmouth sucker and blue head 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 mm 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 Diversion (RK 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 (RK 142.0-199.2). Thirteen wild, adult
Colorado pikeminnow were implanted (tagged) with radio transmi~ters (tags). '
All 16 COlorado pikeminnow captured and tagged between RK 142.0 and 119.2
remained in a 33-mile section of river from RK 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 (RK133.4-l29.8) during presumed
spawning periods. Seven individual adult Colorado pikeminnow were contacted
in or at the mouth of the Mancos River (RK 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.

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