8017

• UCREFRP Catalog Number: 8017
• Author: U.S. Department of the Interior, B. o. R.
• Title: Finding of No Significant Impact, Management and Control of Nonnative Fish Species in Floodplain Ponds along the Upper Colorado and Gunnison Rivers.
• USFW Year: 1998.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

gravel-pit ponds would be suitable for reconnection with the rivers. Many
of the gravel pits are deep -- below the deepest parts of the rivers. Such
ponds may allow nonnative fish species to flourish that would be
counterproductive to recovery of the endangered fishes.

By connecting select floodplain ponds with the river, embayments would be
created that could control reproduction of nonnative fishes while, at the
same time, they would likely benefit the endangered species. Thedeclining
numbers of the endangered Colorado River fishes is attributed to the lack
of recruitment due to low survival from predation and competition by
nonnative fishes and possibly starvation during the critical early 1 ife
stages. It is believed that the high zooplankton productivity would
increase survival in the critical early life stages of the endangered
fishes. Zooplankton densities must be adequate to realize survival of
larval endangered fishes based on studies of razorback suckers by Papoulias
and Minckley (1990). At the same time, nonnative fishes would not be given
the opportunity to multiply in the floodplain ponds since they would enter
the river as the high spring streamflows subside. Earlier in this
Envi ronmenta 1 Assessment, it was stated that the target nonnative fi sh
species for control in floodplain ponds are centrachids, primarily
largemouth bass and green sunfish (Martinez and Nesler 1996). Centrarchid
species do not fare well in the riverine environment based on monitoring of
fish populations by the Recovery Program (McAda et al. 1994 a,b; 1995).

This alternative would be applicable to either natural floodplain
depress ions or gravel-pit ponds in the fl oodp 1 a ins of the Colorado and
Gunnison rivers that connect with the river on a frequent basis. Mitchell
(1995) stated that about 60% of the floodplain ponds, included in his
inventory, connected with the ri vers either annually or one out of ten
years. Reconnect i on of these ponds with the ri,vers woul d allow the
productive off-channel habitats to connect with the rivers annually,
producing zooplankton that are needed by the early life stages of the
endangered fishes.

Burdick (1994) developed a conceptual management plan to experimentally test
the assumptions that were described in the above paragraphs. In the Fall
of 1996, a gravel-pit pond (29 5/8 Road pond) along the Colorado River near
Grand Junction was re-connected with the river. The fish populations using
this manmade "embayment" are currently being monitored by the Colorado River
Fi shery Project of the U. S. Fi sh and Wil dl ife Servi ce in Grand Junction,
Co 1 orado. . Th is experi menta 1 study will provi de ins i ght into the use by
nat i ve fi shes, i nc 1 ud i ng endangered fi shes, and nonnative fi shes. The
results of this experimental field study will be used for decisions on re-
connecting other floodplain ponds with the river and how to best manage such
manmade "embayments" in the future.

Obviously, this alternative has potential for endangered fish recovery in
some of the floodplain ponds but not all. Therefore, it would be premature
to re-connect a large number of ponds with the rivers until the response of
both native and nonnative fishes is better understood.

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