WSP05236

• File Number: 8220.106
• Description: Animas-La Plata
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 2/26/1996
• Title: Final Biological Opinion - 1996
• Water Supply Pro - Doc Type: Biological Opinion

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In the Upper Basin, above Glen Canyon Dam, razorback suckers are found in
limited numbers in both lentic and lotic environments. The largest population
of razorback suckers in the Upper Basin is found in the upper Green River and
lower Yampa River (Tyus 1987). Lanigan and Tyus (1989) estimated that from
758 to 1,138 razorback suckers inhabit the upper Green River. In the Colorado
River most razorback suckers occur in the Grand Valley area near Grand
Junction, Colorado; however, they are increasingly rare. Osmundson and
Kaeding (1991) report that the number of razorback sucker captures in the
Grand Junction area have declined dramatically since 1974.

In the San Juan River subbasin, small concentrations of razorback suckers have
been reported at the inflow area in the San Juan arm of Lake Powell, Utah
(Meyer and Moretti 1988), and one specimen was captured in the San Juan River
near Bluff, Utah, in 1988 (Platania 1990; Platania et al. 1991). In Bestgen
(1990) additional captures of small numbers of razorback suckers also were
reported from the Dirty Devil and Colorado River arms of Lake Powell.

Beginning in May 1987 and continuing through October 1989, complementary
investigations of fishes in the San Juan River were conducted in Colorado,
New Mexico, and Utah (Platania 1990; Platania et al. 1991). In 1987, a
total of 18 adult razorbacks (6 recaptures) were collected on the south
shore of the San Juan arm of Lake Powell (Platania 1990; Platania et al.
1991). These fish were captured near a concrete boat ramp at Piute Farms
Marina and were believed to be either a spawning aggregation or possibly a
staging area used in preparation for migration to some other spawning site.
Of the 12 individual razorbacks handled in 1987, 8 were running ripe males
while the other 4 specimens were females that appeared gravid.

In 1988, a total of 10 razorback suckers were handled at the same general
location, 5 of which were in reproductive condition (Platania et al. 1991).
Six of the ten individual specimens in the 1988 samples were recaptures from
1987. Also, in 1988, a single adult tuberculate male razorback sucker was
captured at approximately river mile 80 on the San Juan River near Bluff,
Utah. Particularly noteworthy is that this is the first confirmed record of
this species from the main stem San Juan River. The presence of this
reproductively mature specimen suggests that the razorback may be attempting
to spawn in some unknown location within the riverine portion of the San Juan
drainage. No razorback suckers were captured in 1989. No larval specimens,
nor any other size classes of razorbacks (other than adults), have ever been
documented in the San Juan River drainage.

All recent captures of wild razorback suckers in the upper basin have been
mature adults. In 1994 an experimental augmentation program was initiated on
the San Juan River; 30 radio tagged razorback suckers and 656 razorback
suckers marked with passive integrated transponder (PIT) tags were released in
the San Juan River. There is no evidence anywhere in the Colorado River
system that indicates significant recruitment to any population of razorback
sucker (Bestgen 1990, Platania 1990, Platania et al. 1991, Tyus 1987, McCarthy
and Minckley 1987, Osmundson and Kaeding 1989).

The existing scientific literature and historic accounts by local residents
strongly suggests that razorback suckers were once a viable, reproducing