7990

• UCREFRP Catalog Number: 7990
• Author: Tyus, H. M.
• Title: Razorback Sucker ‎(
• USFW Year: 1997.
• Copyright Material: NO

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numerous larvae have been captured there from 1980-1996 (Tyus et al. 1987; McAda
et al. 1994;1996; Paul Thompson, UDWR, pers. comm., 1996). Although the fish '
regularly occurs in the lower Yampa, it is rarely found upstream as far as the Little '
Snake River (McAda and Wydoski 1980, Lanigan and Tyus 1989, John Hawkins,
Colorado State University, pars: comm., 1995).
In the upper Colorado River, most razorback suckers occur in the Grand Valley (Valdez
et ai. 1982), but numbers are declinin Osmundson and Kae in 1 ,
9 ( d g 990). Razorback
suckers also may be present in the San Juan River upstream of Lake Powell, but few ,
specmens have been confirmed (Platania et al. 1990, Hinckley et al. 1991). Fifteen
adults have been captured and removed from Lake Powell (11 from the San Juan arm
of the lake and 4 from the Colorado River arm; unpublished USFWS permitting records,
Denver, CO), and a few individuals presumably remain there.
Larval and juvenile razorback suckers have been captured in different locations of the ,
upper Colorado River basin, and especially in the Green River in the last 20 years ,
(Tyus 1987, Gutermuth et al. 1994, Muth 1996), but identification of razorback sucker
larvae has been difficult or impossible when other catostomid larvae were rsen .
p t
Recent advances in taxonomic techniques have made it possible to identify razorback
sucker larvae, even in the presence of other catostomids. Using these new techniques
the Larval Fsh Laboratory at Colorado State University was able to identify 392 larval
razorback suckers in the lower Green River from 1993 to 1996 (Muth 1996). However, '
10 '