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

where levees are breached. Reconnection of breached areas on lowered
floodplains could be made without enhancing streamflows that may cause
economic losses or social issues.

I
I

Depression Ponds. Depression ponds in the floodplain provide habitat
where good to excellent growth of larval and juvenile razorback suckers
and juvenile Colorado squawfish have been demonstrated (Osmundson and
Kaeding 1989). In Humphrey's Pond along the Upper Colorado River,
razorback suckers grew from 55 to 307 mm TL (-2 to 12 inches) from June
until November, 1987 (Figure 3; Osmundson and Kaeding 1989). This growth
is similar to the growth in hatchery ponds. For example, razorback
suckers grew from 44 to 255 mm TL (- 2 to 10 inches) from April until
October, 1993 in Wahweap State Fish Hatchery (Lake Powell), Utah (Figure
3). Twenty-eight Age-O razorback suckers from Old Charley Wash along the
Middle Green River averaged 94 mm TL (- 4 inches) in September and
October, 1995 (Modde 1997). Forty-five Age-O razorbacks from Old Charley
Wash averaged 66 mm TL (- 2.5 inches) in August, 1996. In 1997, 95
juvenile razorback suckers were collected from Old Charley Wash. The
razorback suckers collected from Old Charley Wash were survivors of wild
larvae that entered the wetland during high spring streamflows. Eleven
wild razorback suckers captured in a wetland (Leota Bottom wetland
complex along the middle Green River) in 1994 were between 250 and 370 mm
TL or -10 and -15 inches (Modde and Wick 1997). These fish were
yearlings based on scale analysis and probably entered the wetland in the
spring of the previous year when it was filled with Green River water. A
large number of mature razorback suckers were found in a gravel-pit pond
(Etter's Pond) along the Upper Colorado River in 1990 that apparently
gained access to the pond as larvae during the 100-year floods of 1983
and 1984 (F. Pfeifer, 1994, Personal Communication). However, it is also
likely that these razorbacks were progeny from the spawning of only a few
adult razorback suckers that entered the pond during these floods, based
on mtDNA analysis (B. DeMarais and T. Dowling, 1994, personal
communication). Razorback suckers from the OUray National Fish Hatchery,
Utah, that were surplus to Recovery Program needs, were stocked into golf
course ponds at Page, Arizona where they grew from an average length of
115 mm TL (- 4 inches) to 383 mm (- 15 inches) between May, 1996 and
August, 1997 (Mueller and Wick 1998). Larval razorback suckers stocked
into depression ponds along Lake Mohave have exhibited good growth to
large sub-adults that are stocked into Lake Mohave (Minckley et al. 1991;
Mueller 1995; Mueller et al. 1993).

I

I
I
I

I

I

I

I

If frequency and duration of flooding discussed below cannot be restored,
then captive-rearing of razorback suckers in predator-free floodplain
depressions may be the only course of action left for maintenance of
razorback sucker stocks in the Upper Basin to prevent their extinction.

Reauired Freauency of Floodinq. The frequency of floodplain inundation
required for recovery of razorback suckers is unknown. Numerous
floodplains have been separated from the rivers for a long time so their
potential nutrient levels and productivity are unknown. The flood pulse
concept of nutrient cycling (Junk et al. 1989) provides the productivity
of present Upper Basin rivers because of fragmentation of river reaches
by dams. Therefore, reconnect ion of rivers may be required more often in
the future than when the Upper Basin ecosystem was unaltered.

I
I

I

I

I

The river elevation necessary to provide an adequate frequency of
inundation of floodplain habitats should initially be made on an annual
basis or as often as possible to assist razorback suckers through their
"critical period" that, in turn, should increase survival and
recruitment.

32

I
J
I

I