9694

• UCREFRP Catalog Number: 9694
• Author: Hawkins, J., C. Walford, and A. Hill
• Title: Smallmouth bass control in the middle Yampa River, 2003-2007.
• USFW Year: 2009
• USFW - Doc Type: Contribution 154 Larval Fish Laboratory, Colorado State University.
• Copyright Material: NO

abundance was estimated after two marking occasions (CV = 13%) compared to other
years when abundance was estimated after one marking occasion. Capture probability
of small mouth bass at Lily Park was lowest in 2004 and among all years averaged 9%
(Table 3). Based on point estimates, density of smallmouth bass at Lily Park ranged
247 to 393 fish per mile, over 2.5 times higher in all years than the density of
smallmouth bass at Little Yampa Canyon (Table 4). Boat electrofishing CPUE at Lily
Park declined 33% from 39.6 in 2004 to 26.4 fish/hour in 2007 (Figure 3).

Tag loss- We observed no tag loss that would bias abundance estimates based on
short-term tag loss studies. Of 131 small mouth bass double-tagged in 2007, all 19
recaptures retained both marks, 11-19 days later. Longer-term tag loss was detected
on 40 small mouth bass during the study including: 11 fish with remnants of tags that
appeared to have been cut by fishermen, 28 fish with an injury or scar at the tagging
location indicating possible natural tag loss, and one incidence of tag failure where the
numbered vinyl tubing had detached from the monofilament anchor.

Sampling effort- We electrofished 957 hours with boat electrofishing and 91 hours with
electric seine at the two study sites from 2003 through 2007 (Tables 1 and 2). In 2004
and 2005, we estimated that it would require ten removal occasions to remove 45% of
the adult smallmouth bass in Little Yampa Canyon based on a 6% capture probability
measured in 2003. We actually completed eight removal occasions in each of those two
years. Capture probability improved to 12% and in 2006 we estimated it would require
nine removal occasions to reach our goal of removing 70% of the smallmouth bass in
Little Yampa Canyon. We completed five removal occasions in 2006 and seven in
2007. At Lily Park, removal occasions were tied to northern pike removal and we
targeted five removal occasions per year. We completed five removal occasions in all
but one year at Lily Park. On average, boat electrofishing sampled 6 miles per day and
each mile required 1.2 hours of applied electrofishing time to complete. At each site the
number of hours spent to complete one sample occasion with boat electrofishing was
similar within and among years. Because boat electrofishing effort was consistent

11