WSP02775

• File Number: 8220.106
• Description: Animas-La Plata
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 10/25/1991
• Title: Final Biological Opinion - 1991
• Water Supply Pro - Doc Type: Biological Opinion

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In addition to the eradication project, the physical changes (flow and
temperature) associated with operation of the Navajo Project since closure of
the dam in 1962 have eliminated Colorado squawfish in the upper San Juan River,
from both the reservoir basin as well as several miles of river downstream of
the dam,

A marked decline in Colorado squawfish populations can be closely correlated
with the construction of dams and reservoirs during the 1960's, the
introduction of nonnative fishes, and the removal of water from the Colorado
River system. Behnke and Benson (1983) summarized the decline of the natural
ecosystem, pointing out that dams, impoundments, and water-use practices are
probably the major reasons for greatly modified natural river flows and channel
characteristics in the Colorado River Basin. Dams on the mainstems have
essentially segmented the river system, blocking Colorado squawfish spawning
migrations and drastically altering river characteristics, especially flows,
temperatures, and channel geomorphDlogy. These alterations, which have allowed
nonnative fishes to thrive. caused major changes in species composition.
Haynes et al. (1984) reported that fish species, such as Colorado squawfish,
that evolved under highly fluctuating flow conditions, were better able to
survive and successfully recruit under those conditions than the introduced
species, Valdez (1990) reported that densities of three nonnative cyprinids
(red shiner, sand shiner, and fathead minnow) in the Colorado River were much
lower following high-flow years and increased three to four times in a 2-year
period during normal- and low-water years.

Extreme fluctuations occurring within the framework of a natural annual
hydr~graph may enhance spawning success of native species and inhibit exotic
species, The decline of endemic Colorado River fishes seems to be partially
related to competition or other behavioral interactions with nonnative species,
which perhaps have been exacerbated by alterations in the natural fluvial
environment. Platania (1990) noted that, during the 3 years of studies on the
San Juan River, spring flows and Colorado squawfish reproduction were highest
in 1987, He further noted catch rates for channel catfish were lowest in 1987.
Appendix B, Figure 2, compares the 1987 flow of record to historical conditions
for dry, average, and wet years.

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The Colorado squawfish currently occupies less than 1,000 river miles in the
entire Colorado River system (25 percent of its original range) and natural
populations are presently found only in the Upper Basin above Glen Canyon Dam.
It inhabits about 350 miles of the mainstem Green River from its confluence
with the Colorado River to the mouth of the Vampa River. Its range also
extends 140 miles up the Vampa River and 104 miles up the White River, the two
major tributaries of the Green River. In the mainstem Colorado River, it is
currently found in the 201 miles upstream from Lake Powell to Palisade,
Colorado, and in the lower 33 miles of the Gunnison River, a tributary to the
mainstem Colorado River (Tyus et a1. 1982). Recent investigation (Platania
1990) found that adult Colorado squawfish currently inhabit the San Juan River
as far upstre.. as 163.3 miles above Lake Powell.

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