2008-04-04_PERMIT FILE - C1981038A

• Permit No: C1981038A
• IBM Index Class Name: Permit File
• Doc Date: 4/4/2008
• Section_Exhibit Name: Environmental Resources - Fish & Wildlife Appendix Part 3
• Media Type: D
• Archive: Yes

• 9
A marked decline in populations of razorback suckers can be attributed to
construction of dams and reservoirs, introduction of nonnative fishes, and
removal of large quantities of water from the Colorado River system. Dams on
the main stem Colorado River and its major tributaries have segmented the
river system and drastically altered flows, temperatures, and channel
geomorphology. Major changes in species composition have occurred due to the
introduction of numerous nonnative fishes, many of which have thrived due to
man-induced changes to the natural riverine system.
The current distribution and abundance of the razorback sucker have been
significantly reduced throughout the Colorado River system (McAda 1987; McAda
and Wydoski 1980; Holden and Stalnaker 1975; Minckley 1983; Marsh and Minckley
]989; Tyus 1987). The only substantial population of razorback suckers
remaining, made up entirely of old adults (McCarthy and Minckley 1987), is
found in Lake Mohave; however, they do not appear to be successfully
recruiting. While limited numbers of razorback suckers persist in other
locations in the Lower Colorado River, they are considered rare or incidental
and may be continuing to decline.
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 has declined dramatically since 1974.
Razorback suckers are in imminent danger of extirpation in the wild. The
specific causes of this species' continued decline are largely unknown at this
time. As Bestgen (1990) pointed out:
"Reasons for decline of most native fishes in the Colorado River
Basin have been attributed to habitat loss due to construction of
mainstream dams and subsequent interruption or alteration of natural
flow and physio-chemical regimes, inundation of river reaches by
reservoirs, channelization, water quality degradation, introduction
of nonnative fish species and resulting competitive interactions or
predation, and other man-induced disturbances (Miller 1961, Joseph
et al. 1977, Behnke and Benson 1983, Carlson and Muth 1989, Tyus and
Karp 1989). These factors are almost certainly not mutually
exclusive, therefore it is often difficult to determine exact cause
and effect relationships."
The virtual absence of any recruitment suggests a combination of biological,
physical, and/or chemical factors that may be affecting the survival and
recruitment of early life stages of razorback suckers. Within the Upper
Basin, recovery efforts endorsed by the Recovery Implementation Program
• include the capture and removal of razorback suckers from all known locations
for genetic analyses and development of discrete brood stocks if necessary.
These measures have been undertaken to develop refugia populations of the