9410

• UCREFRP Catalog Number: 9410
• Author: Wydoski, R. S. and E. J. Wick.
• Title: Ecological Value of Floodplain Habitats to Razorback Suckers in the Upper Colorado River Basin.
• USFW Year: 1998.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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floodplain ecosystem of the Upper Colorado River Basin must be restored
if recovery of the endangered fishes is to be achieved.

Re-introduction stocking of razorback suckers in the upper Colorado and
Gunnison rivers and augmentation stocking in the middle Green River
should be continued following approved stocking plans and genetics
conservation measures (Williamson and Wydoski 1994) to increase numbers
of razorback suckers in those rivers. Although augmentation stocking is
not recovery, it provides a mechanism to maintain adult razorback suckers
in the upper Colorado River Basin to prevent extinction until a solution
is found to achieve self-sustaining populations (i.e., recovery).

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Evaluate factors identified in a stocking plan that may affect survival
of captive-reared fish including (1) use of floodplain ponds as a "half-
way" habitat where captive-reared razorback suckers can become
conditioned to eating natural food organisms, (2) importance of physical
conditioning to various water velocities prior to release, (3) size of
fish at release, (4) time of release, etc. Experimental stocking in the
Green and Gunnison rivers with captive-reared fish of 100 mm TL (- 4 in)
has not been successful. Few of the fish were recovered shortly after
stocking and recaptures have not been made. However, seven razorback
suckers were recaptured in 1997 from 1,068 that were stocked as larger
fish (209-308 mm TL; - 8-12 in) into the middle Green River in 1996 (T.
Pruitt, 1998, personal communication) .

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Recaptures of razorback suckers stocked into the San Juan River (F.
Pfeifer, 1997, personal communication) suggested that larger fish may
survive better than small fish. Although survival of juvenile razorback
suckers that were stocked at 113 mm TL (- 4 in) into the Gila River,
Arizona increased because of less predation by ictalurids, Marsh and
Brooks (1989) recommended stocking fish that are 300 mm TL (12 in) or
larger in the Lower Colorado River Basin. Recaptures of fish stocked at
300 mm TL has been considered successful in Lake Mohave (G. Mueller,
1996, personal communication). The former Recovery Program Propagation
Coordinator (RSW) recommended that fish 300 mm TL ( - 12 in) or larger
should be stocked in the Upper Colorado River Basin. Razorback suckers
in floodplain ponds along Upper Basin rivers will grow to 300 mm TL (- 12
in) by the end of the second growing season (Figure 3). Fish that are
reared in floodplain ponds would reach 400 mm TL (16 in) or larger by the
end of the third growing season. Fish stocked after three seasons of
growth in the fall should mature and produce larvae in Upper Basin rivers
the following spring.

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In conclusion, the Recovery Program elements of (1) streamflow, (2)
habitat enhancement/restoration, (3) control of nonnative fishes and (4)
captive propagation/ stocking of razorback suckers must be integrated
conscientiously and concurrently because these four Recovery Program
elements are closely interconnected and are expected to affect the
responses of native (including endangered) and nonnative fishes.

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