GENERAL31841

• Permit No: M1999002
• IBM Index Class Name: General Documents
• Doc Date: 7/22/1999
• Doc Name: FINAL ENVIRONMENTAL IMPACT STATEMENT VOLUME 2 APPENDIX L
• Media Type: D
• Archive: No

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upper Green River and lower Yampa River (Tyus 1987). ]~anigan and Tyus
(1989) estimated that from 758 to 1,138 razorback suckers inhabit the
upper Green River. Modde et al. (1996) report no significant decrease
in the population between 1982 and 1992, and the conti~lued presence of
fish smaller than 480 mm during the study period suggest some level of
recruitment. In the Colorado River, most razorback su~~kers occur in
the Grand Valley area near Grand Junction, Colorado; h~~wever, they are
increasingly rare. Osmundson and Kaeding (1991) repor•= that the
number of razorback sucker captures in the Grand Junction area has
declined dramatically since 1974. In 1991 and 1992, 23 adult
razorback suckers were collected from isolated ponds adjacent to the
Colorado River near DeBeque, Colorado (Burdick 1992). The existing
habitat has been modified to the extent that it impairs essential
behavior patterns, such as breeding, feeding, and sheltering.
Razorback suckers are in imminent danger of extirpation in the wild
The razorback sucker was listed as endangered October 23, 1991
(56 FR 54957). 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 factor:; 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 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 razorback sucker from
the same genetic parentage as their wild counterparts such that, if
these fish are genetically unique by subbasin or individual
population, then separate stocks will be available for future
augmentation. Such augmentation may be a necessary step to prevent
the extinction of razorback suckers in the Upper Basin.
McAda and Wydoski (1980) and Tyus (1987) reported springtime
aggregations of razorback suckers in off-channel habitats and
tributaries; such aggregations are believed to be asscciated with •