9688

• UCREFRP Catalog Number: 9688
• Author: Upper Colorado River Endangered Fish Recovery Program.
• Title: Nonnative Fish Control Workshop Summary, Conclusions, and Recommendations.
• USFW Year: 2002.
• USFW - Doc Type: Lakewood, CO.
• Copyright Material: NO

Table 5. Sampling effort and numbers of northern pike and Colorado pikeminnow captured '
during 1999-2001.
Year Sampling Effort (samples) Numbers of Fish Captured
Electrofishing Fyke Nets Northern Pike Colorado
Pikeminnow Ratio
1999a 72 23 3.1:1.0
2000 61 560 443 83 5.3:1.0
2001 185 250 269 140 1.9:1.0
Totals 246 810 784 246 3.2:1.0
aOnly block and shock used in 8 backwaters; 14 samples.

'~

Average lengths of northern pike for each of four trips in 2001 were significantly greater than
average lengths during the four trips in 2000. r
Bite marks were found on all sizes of Colorado pikeminnow examined during 1999-2001, with
the largest in the 650-700 mm TL range (Figure 16). During 1999, only about 15% of Colorado '
pikeminnow had bite marks, but in 2001, approximately 30% had bite marks.
This study concluded that northern pike occurred in concentrations in the Yampa River, '
primarily in and around backwaters (i.e., floodplain habitats) during spring runoff. Hence, the
most effective time and manner for capturing these fish was by sampling in and near backwaters '
during spring runoff. Northern pike outnumbered Colorado pikeminnow at three sample
locations on the Yampa River by about 2-3:1, and 10:1 in some locations. Total numbers of
northern pike removed and translocated from the Yampa River during 1999-2001 was 784. '
Average length of northern pike did not decline on successive sampling occasions; average
length in 2000 was 550 mm TL, and average length in 2001 was 600 mm TL. This suggests that
removal efforts during 1999-2000 removed the smaller fish, or growth was manifest in the '
remaining fish and average size 1 year later was greater.
Cursory examination of stomachs and regurgitated contents showed that northern pike prey on '
large-bodied native fishes, including roundtail chub and flannelmouth sucker. Scars on Colorado
pikeminnow were evidence of attempted predation by northern pike on even large pikeminnow.
A Lincoln-Petersen mark-recapture estimate yielded an estimated 1,350 northern pike (95% '
confidence interval = 959-2067; standard error = 261; capture probability = 0.06) in the reach of
the Yampa River sampled. Translocation of northern pike from the Yampa River will continue
in 2002 and 2003 with continued evaluation of effectiveness of removal. '

29 '
n