9555

• UCREFRP Catalog Number: 9555
• Author: Bestgen, K. R., C. D. Walford, A. A. Hill and J. A. Hawkins.
• Title: Native Fish Response to Removal of Non-native Predator Fish in the Yampa River, Colorado.
• USFW Year: 2007.
• USFW - Doc Type: 140,
• Copyright Material: NO

METHODS
Fish removal studies background.- Although not specifically part bf this study (see
Hawkins 2005, 2006), the structure and effort allocated to predator fish remo~al in the study area
is detailed below to assist the reader with understanding important aspects of ~he experimental
design for this study. In 2003-2005, smallmouth bass sampling was stratifiedby treatment and
control reaches. The first sampling pass was typically a marking pass for nor
smallmouth bass and recapture data from subsequent passes were used to cor.
estimates for those species by reach. smallmouth bass captured after the firs
treatment reach were removed from the river but in the control reach, bass we
Northern pike were removed from all areas after marking passes were comply
reach). Removal sampling was mainly directed at larger-bodied age-1+ sma
pike. In 2006, the entire 38.6 RK study area was a removal (treatment) area ~
northern pike. This was done because smallmouth bass movement was exten
shorter control and treatment reaches, such that removal efforts were confour
The control-treatment aspect of this study was maintained by additi
small-bodied smallmouth bass (mostly age-0, some age 1 bass) and other
treatment reach in late July through early September, beginning in 2005 and
2005, 2006). This additional removal was the result of insufficient
pike and
luct abundance
pass in the
re released alive.
ted (e.g., no control
mouth bass and
.r bass as well as
ive within the
led.
1 removal of
ators from the
306 (Hawkins
oflarger-bodied
smallmouth bass that would subsequently spawn and produce large numbers fsmall-bodied
smallmouth bass. Because we thought a response to non-native predator rem val would be first
and most easily observed in small-bodied native fishes, and that small-bodie bass were mostly
likely the strongest predatory influence on small-bodied native and other fish s, increased
removal of small-bodied bass seemed a logical addition to achieving study o jectives. This logic
also led us to focus exclusively on sampling small-bodied fish to document r sponse to non-
native fish removals.
Small-bodied smallmouth bass removal in 2005 and 2006 in the 19 R~ treatment reach
was mainly with a crew of four or five and a 10 m-long electric seine (Hawk~ns 2005, 2006).
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