WSP03464

• File Number: 8240.300.31.J
• Description: San Juan River - Environmental Studies
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 5/12/1995
• Title: Biological Evaluation of a Proposal to Stock Non-Native Fishes into Ponds within the 0- to 50-year Floodplain of the Upper Colorado River Basin in Critical Habitat of Endangered Fishes
• Water Supply Pro - Doc Type: Report/Study

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Four big-river fishes of the Colorado River have been listed
by the D,S. Fish and Wildlife Service [FWS) as endangered:
Colorado squawfish (Ptychocheilus lucius), razorback sucker
(Xyrauchen texanus), humpback chub (Gila cypha) , and bony tail
chub [Gila elegans) . Numerous recovery and implementation plans
have been written, well over 100 scientific papers have been
published, and millions of dollars have been spent, all toward
the recovery of these four endangered species. Most of the
critical threats to these four species center around loss of
habitat. and include: instream flow, non-native fish predation
and competition, and macro- and micro-habitat availability and
utilization,

Recovery efforts for the Colorado River fishes have been
divided geographically into Upper Basin and Lower Basin due to
differences in remaining habitats and stocks. The recovery'
program for the endangered fishes of the Upper Colorado Basin is
centered in FWS in Denver, Colorado. FWS personnel work in
conjunction with Colorado Division of Wildlife, Utah Division of
Wildlife Resources, wyoming Game and Fish Department, and a
multitude of private, state, and federal organizations toward the
eventual re-establishment of self-sustaining populations of the
four fishes while providing for future water development.

Numerous nonnative fishes have been implicated in impacting
endangered fishes in the Upper Basin. The most detrimental is
thought to be channel catfish (Ictalurus punctatus), which
dominates the upper Colorado and Green rivers and their
tributaries, and reproduces within the mainstream. Other
nonnative fishes believed to be detrimental include: green
sunfish (Lepomis cyanelllus), fathead minnow (Pimephales
promelas), red shiner (Cyprinella lutrensis), common carp
(Cyprinus carpio), redside shiner (Richardsonius balteatus),
northern pike (Esox lucius) , mosquitofish (Gambusia affinis), and
largemouth bass. Biologists familiar with these rivers and
fishes suggest that many of these species do not maintain
breeding populations within the mainstream, and their presence
depends upon continuous immigration from off-river ponds during
relatively frequent flooding. Black crappie are within the
watershed, but are not known to have been taken from the
mainstream rivers or their riverine tributaries,

Recently, Colorado Division of Wildlife (DOW) has proposed
to stock nonnative game fishes into ponds within the floodplain
of the Colorado River in Colorado, including largemouth bass
(Micropterus salmoides), bluegill (Lepomis macrochirus), and
black crappie (pomoxis nigromaculatus). All three of these non-
native fishes are piscivorous, which raises concern over their
movement into the Colorado River and subsequent impact on the
endangered fishes there. FWS has discussed the proposal with
DOW, the neighboring states, and cooperating agencies, and has
begun to consider ideas that could provide for both the