7996

• UCREFRP Catalog Number: 7996
• Author: Wydoski, R. S. and E. D. Wick.
• Title: Ecological Value of Flooded Bottomland Habitats to Endangered Fishes in the Upper Colorado River Basin.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

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I. ABSTRACT

The declining numbers of some endemic Colorado River fishes is attributed to low
or the complete lack of recruitment. Although the long-lived endangered fishes
spawn successfully and produce 1 arvae, high mortal ity during the early 1 ife
stages limits recruitment with the result that some native fish stocks are no
longer self-sustaining. Four native fishes (razorback sucker, bony tail , humpback
chub, and Colorado squawfi sh) are 1 i sted as endangered under the Endangered
Speci es Act.

The Biology Committee members have agreed that Colorado squawfish and humpback
chub stocks below impassable barriers appear to be stable and recruitment has
been documented (Wydoski 1994). However, it is not known with certainty whether
present recruitment is adequate to maintain self-sustaining populations. The
bony tail has declined to the point where only occasional specimens are captured
in the upper basin with long periods of time and long distances between captures.
Potential hybridization of bony tail with other Gila in the upper basin poses
genetic risks that may limit reintroduction efforts of the bony tail into its
historic range.

The razorback sucker is considered the primary species where recovery efforts may
re-establish the species in the Upper Colorado River and restore the remaining
middle Green River stock (Wydoski 1994). Enhancement or restoration of
fl oodp 1 a in habitats through reconnect i on wi th upper bas i n ri vers wi 11 improve the
productivity of the ecosystem for zooplankton and benthic invertebrates required
by the early life stages of the razorback sucker. Any enhancement or restoration
endeavors must be made through experiments that are thoroughly evaluated using
the adaptive management approach. Attempts to restore large areas of floodplain
habitats would preclude adequate evaluations and refinements using the adaptive
management approach. Limited areas that are enhanced or restored shoul d be
thoroughly evaluated and refinements made as necessary to determine the responses
of the endangered and nonnative fishes to such efforts.

The removal of levees that are on the lowest floodplain terraces, coupled with
higher spring streamflow releases that mimic the historic hydrographs from
upstream dams, provide the best way to reconnect mainstem and tributary rivers
with product i ve fl oodp la ins. Such removal should be done on low fl oodp 1 a in
terraces on pub 1 i c propert i es that can be eas il y reconnected wi th the ma in
channel and where thorough evaluations can be made. Experiments on publ ic
property would preclude extremely high releases that would cause sociological
problems associating with the flooding of private agricultural lands and the
production of mosquitoes that could pose human health problems. If the
experiments performed on public property are successful and it is determined that
more floodplain habitat is needed for restoration, then leasing of private lands
can be explored and implemented.

However, some nonnative fi shes that are estab 1 i shed in the upper bas in will
flourish in productive off-channel habitats. If the duration of inundation of
off-channel habitats is short, razorback suckers will not grow to a size where
predation and competition by nonnative fishes is no longer a principal factor in
their survival. If the duration of flooding these habitats is longer, nonnative
fishes will flourish and continue to adversely affect larval and juvenile
razorback suckers. These nonnative fish interactions may limit the recovery of
the razorback sucker unless adequate control measures can be implemented in