9449

• UCREFRP Catalog Number: 9449
• Author: Hawkins, J. A.
• Title: Recapture and growth rates of three Colorado River endangered fish species
• USFW Year: 2003.
• USFW - Doc Type: a comparison between electrofishing and non-electrofishing.
• Copyright Material: NO

electrofishing were similar to the effects of non-electrofishing sampling gears. All
sampling gears were assumed to have some negative effects on the captured animal.
The critical issue was whether electrofishing had greater negative effects on the animal
than other non-electrofishing sampling- gears. Effects were measured at both individual
and population levels. Population-level effects were measured with recapture rate that
represented a relative index of fish survival for each sampling gear type based on the
assumption that recapture rate would be lower if a particular sampling gear caused
higher post-sampling mortality. The hypothesis was that recapture rates of each
species were similar for the two gear types (electrofishing ornon-electrofishing).
Individual-level effects were measured by examining growth rate, an important indicator
of fish health. It was assumed that nonlethal, negative effects of a sampling gear would
reduce fish growth. I compared growth offish captured by electrofishing to growth of
fish captured by non-electrofishing gears to test the hypothesis that growth rates were
similar for the two gear types.
METHODS
Endangered fish capture data were obtained from the data repository at the U.S.
Fish and Wildlife Service (USFWS),Grand Junction, Colorado field station, agency
reports, and individual researchers to create a working database of capture events in
the Upper Colorado River Basin. The database contained unique records for each
capture event of a tagged fish. Each uniquely-tagged fish had at least one record for
the initial capture and tagging event and if a fish was recaptured there was a record for
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