7370

• UCREFRP Catalog Number: 7370
• Author: Platania, S. P.
• Title: Biological Summary of the 1987 to 1989 New Mexico-Utah Ichthyofaunal Study of the San Juan River.
• USFW Year: 1990.
• USFW - Doc Type: Albuquerque, New Mexico.
• Copyright Material: NO

Mexico) and Robertson (1977) summarized and discussed the results
of Smith's 1975 ichthyofaunal survey of the Mancos River system.
While none of these investigations resulted in the collection of
Colorado squawfish or razorback sucker, they provided important
documentation of the continued occurrence of roundtail chub in
tributary systems and the mainstem San Juan River.
The two most extensive and significant surveys of the San
Juan River since Olson's 1961 work (Olson 1962) were those
conducted by Sublette (1977), and VTN Consolidated, Inc. and
Museum of Northern Arizona (1978). Sublette and his associates
collected at 34 stations on the San Juan River and its
tributaries from Pagosa Springs, Colorado to the vicinity of
Mexican Hat, Utah. During the course of the survey, Sublette
took four roundtail chub at two locations, but did not collect
any of the other target species. This contrast to Olson's (1962)
work 15 years earlier was alarming, but Sublette (1977) noted
that the absence of target species, except roundtail chub, in his
collections did not preclude their occurrence in the study area.
VTN Consolidated, Inc. and the Museum of Northern Arizona
(1978) made 18 electrofishing and seining collections in the San
Juan River between Navajo Dam, New Mexico and Clay Hills
Crossing, Utah. They collected (photographed and released) a 177
mm total length (TL) juvenile Colorado squawfish in the San Juan
River five miles (8 km) downstream of Aneth, Utah. In addition,
they reported (second-hand) the capture in 1976 of two adult
razorback sucker from an irrigation pond near Bluff, Utah.
The capture in 1978 of a juvenile Colorado squawfish (VTN
Consolidated, Inc..and the Museum of Northern Arizona 1978) and
1977 report of an adult from the San Juan River arm of Lake
Powell (U.S. Fish and Wildlife Service 1981) resulted in several
supplementary investigations of the physical and biological
components of the San Juan River. The benthic, planktonic, and
invertebrate-drift communities of the San Juan River at 20
stations between Navajo Reservoir, New Mexico, and Mexican Hat,
Utah were inventoried by Holden et al. (1980). Twedt and Holden
(1980) estimated habitat availability and developed habitat
suitability curves for Colorado squawfish in the San Juan River,
New Mexico and Utah. O'Brien (1987) investigated levels of
organochlorine and heavy metal contamination in-fishes from the
New Mexico portion of the San Juan River fishes in 1984.
In recent years, most of the ichthyofaunal studies of the
endangered Colorado River basin fishes have concentrated on the
Upper Mainstem Colorado River and Green River sub-basins. The
San Juan River Sub-basin has not been emphasized because it was
believed that, even though Colorado squawfish and Gila species
were historically known to occur in the region, they were rare
(Tyus et al. 1982) or extirpated (Holden and Wick 1982). These
presumed declines were associated with changes in discharge
patterns and physico-chemical parameters brought about by closure
of Navajo Dam.
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