8204

• UCREFRP Catalog Number: 8204
• Author: Tyus, H. M.
• Title: Razorback Sucker ‎(Xyrauchen texanus)‎ Recovery Plan.
• USFW Year: 1998.
• USFW - Doc Type: Boulder, Colorado.
• Copyright Material: NO

which pose a serious threat to the razorback sucker, are present in all 15 reaches of
critical habitat. Also included are areas in which critical habitat for the razorback sucker
overlaps with that of other listed species (after Maddux et al. 1993, USFWS 1994):
RZ1: Yampa River section from Cross Mountain Canyon to Green River.
The lower reaches of the Yampa River provide adult and spawning habitat, and
potential nursery areas occur downstream. The existing water quantity and
quality conditions are relatively unaltered from historic conditions. Tyus and
Karp (1989) found the existing flows in this reach adequate for life history needs
of the native fishes, principally because spring flows and baseline conditions are
little changed from historic conditions. The primary threat to razorback sucker
survival and recruitment in this reach is the abundance of nonnative fish species
that prey upon or may compete with the razorback sucker, and the State of
Colorado has removed bag and possession limits for predaceous warmwater
game fish within critical habitat. Protection of the Yampa River will maintain its
contribution of flow and nutrients to important downriver reaches (RZ2 and RZ3)
on the Green River (McAda and Wydoski 1980; Tyus and Karp 1989).
RZ2: Green River section from mouth of Yampa River to Sand Wash.
This reach of the Green River contains the largest existing riverine population of
the razorback sucker (Lanigan and Tyus 1989, Modde et al. 1996). The reach
provides spawning (Tyus and Karp 1990) and nursery habitat (Wick et al. 1982).
Flaming Gorge dam prevents upstream movement and, in combination with the
Fontenelle dam, alters water flows, temperature regimes, and sediment, and
contaminant concentrations. The dams are presently providing some flows
needed by the endangered fishes, and the Service and the Bureau of
Reclamation are studying this reach for determining water flow needs of the fish.
However, Stephens et al. (1992) found sufficient levels of boron, selenium, and
zinc in water, sediment, and fish tiss~le samples to be harmful to fish in some
restricted locations. Selenium levels from one impounded area are elevated and
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