WSP00586

• File Number: 8240.300.02
• Description: San Juan River Recovery Implementation Program - Recovery Plans & Information
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 1/1/1999
• Title: San Juan River - Recovery Implementation Program ‎(RIP)‎ -- Executive Summaries - 1999 to Present
• Water Supply Pro - Doc Type: Report/Study

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Using a Schnabel population estimate, the number of COlorado pike~innow
between aM 136.6 and 119.2 for the period between June 1991 and October 1995
was estimated at 19 fish (based on 15 sampling trips). Ninety-five percent
confidence intervals place the range of this population at 10-42 COlorado
pikeminnow. Petersen index population estimates for the same time period and
group of river ~iles place the COlorado pikeminnow population between 9 and 20
fish (based on the 14 sampling intervals).
Five major instream diversion structures in the san Juan River between RM
178.5 and 142.0 impede fish movements to varying degrees. Of these
diversions, the San Juan Generating Station (PNM) Weir is probably the
greatest barrier to native fish movements. However, the PNM Weir also appears
to be inhibiting the upstream spread of channel catfish.
Walleye and striped bass invaded the San Juan River from Lake Powell in
1995 when rising lake levels inundated the waterfall at RM 0.0. These species
have been documented to prey upon native flannelmouth sucker. The presence of
these aggressive lacustrine predators coupled with the already large numbers
of nonnative fish species that compete with and prey upon native species,
complicates recovery efforts for endangered fishes in the San Juan River.
Both endangered Colorado pikeminnow and razorback sucker have been
collected within the San Juan River of Lake Powell and the lake influence zone
in the San Juan River. Both of these species have been documented moving
upstream from Lake Powell into the San Juan River when the waterfall at RM 0.0
was not present. So, while the waterfall protected native fishes in the San
Juan River from predatory lacustrine fishes, it also kept rare fish species in
Lake Powell from communicating with riverine populations.

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