WSP11103

• File Number: 8240.300.10
• Description: San Juan Recovery Implementation Program
• Basin: San Juan/Dolores
• Date: 2/1/1995
• Author: SJRIP
• Title: San Juan River Basin Recovery Implementation Program - Program Document
• Water Supply Pro - Doc Type: Publication

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decisions and actions.

b. Implementation Program Participants will pursue actions
necessary to bring about water quality improvements
found necessary for recovery of the endangered fish
species and conservation of other native fish species
populations consistent with state and federal
regulations.

c. Measures will be taken to diminish or eliminate sources
of contaminants that are identified as limiting
recovery of endangered fish species populations.

3.5 INTERACTIONS BETWEEN NATIVE AND NON-NATIVE FISH SPECIES

3.5.1 Statement of Problem

The native fish fauna of the Colorado River drainage historically
was comprised of 14 species, including six that are endemic to
the system. Compared to the fish fauna of more mesic regions,
that of the Colorado River is depauperate. Native Colorado River
drainage fishes evolved in a system characterized by extreme
seasonal fluctuations in flow regimes. Habitats ranged from
small, headwater tributaries where coldwater-tolerant forms such
as Colorado River cutthroat trout were abundant to large,
turbulent, silt-laden rivers where especially adapted forms such
as humpback chub and Colorado squawfish flourished. Other
species such as speckled dace and flannelmouth sucker, more
generalist in adaptations, were widespread and common in suitable
habitats.

Modification of aquatic systems to satisfy human desires
diminished availability and quality of habitats suitable for
native fishes and, therefore, many species declined dramatically
in distribution and abundance. Human-induced habitat
modifications also created conditions conducive to establishment
of non-native fish species. Since the late 1800's, at least 40
non-native fish species have been introduced intentionally or
accidentally to the rivers and reservoirs of the Upper Colorado
River Basin. The specific role of any single non-native species
in the decline of a native fish species is difficult to assess,
and several non-native species negatively interact with native
species in multiple manners. Non-native fish species, such as
red shiner and northern pike, compete with or prey upon native
fishes, a few, such as rainbow trout, hybridize with and compete
for resources with native fish species, and others, such as
fathead minnow and plains killifish, have no discernable or
demonstrated effect. Some non-native species occur infrequently
or in such low numbers (e.g., green sunfish in the San Juan
River) that their impact on native fishes is limited, if any.
Several non-native fish species (red shiner and channel catfish)
compete with or prey upon early life stages of native fishes and