WSP01579

• File Number: 8240.200.10.B
• Description: UCRBRIP Annual Report
• Basin: Colorado Mainstem
• Date: 12/22/1997
• Author: UCRBRIP
• Title: 1997 Annual Reports Package Part 2
• Water Supply Pro - Doc Type: Publication

on the endangered fishes of the upper Colorado River basin; 46% of
respondents believed" northern pike Esox lucius to be an important
problem for the native fish community.

Northern pike were stocked into paonia Reservoir on the North Fork of
the Gunnison River in 1969 and 1971. Some,fish escaped and
established a small population within critical habitat on the
Gunnison River near Delta, Colorado. No ~epraduction has been
documented in the Gunnison River and the population apparently relies
on continued escapement from paonia Reservoir to maintain itself.
This study was conducted to determine if the population could be
substantially reduced through mechanical removal.

Previous work identified a 16-km-long river reach downstream from
Hartland Diversion where most northern pike were collected. Sampling
efforts targeted that reach. sampling was concentrated in spring
when high water provided quiet, off-channel habitats that were
believed to attract northern pike. Workers used electrofishing, fyke
nets and trammel nets to intensively sample areas where northern pike
had been collected in the past. In contrast with other studies,
shoreline electrofishing was the most effective sampling technique
for collecting northern pike in the Gunnison River.

A total of ten northern pike were collected and removed from the
study area in 1995 and 1996. Six of those pike were captured on the
first day of sampling in 1995. Intensive sampling by two-person
crews for 27 more days captured three more northern pike. Thirteen
days of sampling in 1996 captured one additional northern pike. One
pike was observed that could not be captured. The abrupt decline in
catch per effort and the sustained low catch rate thereafter indicate
that a small population with limited recruitment can be substantially
reduced with mechanical means. It is unlikely that all northern pike
occupying the area were captured and removed; however the low catch
rate in 1996 suggests that most were.

Based an one year of data, movement af northern pike into the area
from the upstream reservoir is slow. However, northern pike will
gradually reoccupy critical habitat. Sampling should be repeated
regularly (every two to four years) to remove additional pike that
occupy the area. Relatively limited sampling at the right time and
with the right gear can remove most of the pike. Northern pike use
of the study area will be a chronic problem until they are eliminated
from Paonia Reservoir-the apparent source of all pike in the Gunnison
River.

The final report for this study
final by the Biology Committee.
199B.

has been completed and accepted as
It will be distributed in early

VII. Recommendations:

Northern pike should be removed from the Gunnison River downstream
from Hartland Diversion on a regular basis (intervals of 2-4 years).
Sampling to remove pike should be timed to correspond with river
flows of 85-113 m'ls to be most effective. One week of effort at the

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