9689

• UCREFRP Catalog Number: 9689
• Author: Recovery Implementation Program.
• Title: Recovery Implementation Program For Endangered Fish Species In The Upper Colorado And San Juan River Basins - 27th Annual Recovery Program Researchers Meeting Program.
• USFW Year: 2006.
• USFW - Doc Type: Moab, UT.
• Copyright Material: NO

marked and released on the first pass, and removed on subsequent passes. Removal
success was evaluated using program MARK to generate a capture-recapture abundance
estimator. Seven hundred and one (701) northern pike were estimated to occupy the
critical habitat reach (573-891 95% CI; SE=80.3; CV=0.115). Capture probability was
22%, similar to that observed in 2004 (23%). The number of northern pike captured in
2005 was less than the number reported by Hawkins for the same reach in 2004.
Hawkins estimated 974 northern pike occupying the study area in 2004 (769-1279 95%
CI; SE=128.5; CV=0.132). In 2005,59% of the estimated population of northern pike
was removed from the middle Yampa River. Nearly 90% of the northern pike removed
were translocated to Loudy Simpson ponds and Rio Blanco Lake to provide angler
sportfishing opportunities. No clear patterns were observed with catch rates (numbers of
northern pike per hour and per river mile). A large number (112) of northern pike
handled and released on the fIrst pass were never recaptured. The average total length of
northern pike captured increased in a downstream direction. Recaptured northern pike
traveled considerable distances over a relatively short time period of less than two
months; two fish traveled more than 40 river miles. Ninety three percent (93%) of the
northern pike recaptured had moved more than one river mile downstream.
Recommendations for future efforts include: standardizing electrofishing equipment and
operating protocol; exploring other potential metrics for population assessment;
increasing backwater sampling effort; exploring baiting, trapping, and chumming
options; and continuing contacts with Yampa River landowners and stakeholders.

13. A Preliminary Examination of Crayfish in the Yampa River in Northwestern
Colorado

Authors: PATRICK MARTINEZ, MICHAEL CARILLO, ELLEN HAMANN,
KELLEN KEISLING and MARIO SULLIVAN, Colorado Division of Wildlife, 711
Independent Avenue, Grand Junction, CO 81505, Phone [phone], FAX. 970-255-
6111, [e-mail]

Abstract: No crayfish species are native to the Colorado River Basin, but several
introduced species have become established. The verile crayfish Orconectes viri/is has a
wide distribution in the Colorado River Basin and is its most common crayfish species.
This species is established in many waters in western Colorado where it has been widely
introduced into reservoirs to improve the prey base for sport fish. This species also
occurs in many streams, including western Colorado's "big rivers". While crayfish were
known to occur in the Yampa River, there appeared to be an abrupt increase in their
numbers in recent years as perceived by fishery biologists. This apparent explosion in
verile crayfish numbers coincided with extreme drought conditions and the onset of an
increasingly abundant population of nonnative smallmouth bass Micropterus dolomeiu.
Crayfish density was estimated at three stations in the middle reach of the Yampa River
in 2005 using I_m2 square plots along randomly selected transects perpendicular to the
channel. The sampling resulted in an estimated standing crop of90 kg of veri Ie crayfish
per hectare. Despite decimation of the small-bodied component of the fish community in
reaches of the middle Yampa River, smallmouth bass maintain high relative weights and
their diet is dominated by crayfish. Available historic diet data for channel catfish

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