7784

• UCREFRP Catalog Number: 7784
• Author: Snyder, D. E.
• Title: Impacts of Electrofishing on Fish.
• USFW Year: 1992.
• USFW - Doc Type: \
• Copyright Material: NO

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Impacts of Electrofishing on Fish

Introduction 1

INTRODUCTION

Electrofishing, the use of electric fields in water
to capture or control fish, has been a valuable
sampling technique in North America for four
decades, but it is now in a state of flux. The use of
electrofishing is expanding with new equipment and
applications, but it is also being limited by increasing
concerns for comparability of data, operator safety,
and injury to fish.
The present concern over electrofishing injuries
was sparked by Sharber and Carothers' 1988
publication which documented substantial and
unexpected injury to the spine and associated tissues
of 44 to 67% of the rainbow trout (Oncorhynchus
mykiss, >300 mm TL, total length) electrofished with
modem equipment and pulsed direct current (pDC).
Most of the injuries were detected only by X-ray
analysis or necropsy in fish that otherwise appeared
quite normal (Figure 1). Such spinal injuries have
long been associated with use of altemating current
(AC), but until now, had been largely overlooked as
a significant problem with most forms of PDC. This
situation persisted despite much earlier publications
documenting high incidence of injury with PDC. For
example, Horak and Klein (1967) observed
indications of probable spinal injury in 39% of the
hatchery-reared rainbow trout they electrofished with
60-Hz PDC.
The renewed concern about potential
electrofishing injury has prompted biologists and
managers in several agencies to investigate the
existence and extent of the problem in their own
situations. Reports by Holmes et al. (1990),
McMichael et al. (1991; also McMichael and Olson
unpubl. ms. 1991), Meyer and Miller (1990, 1991,
unpubl. ms 1991; also Wyoming Game and Fish
Department 1990, 1991), Fredenberg (1992),
Hollander and Carline (1992), Newman (1992,
unpubl. ms. 1991), Reynolds et al. (1992), Roach
(1992), and Taube (1992) have similarly documented
substantial PDC-caused spinal injury not only in
rainbow trout (up to 98%), but in cutthroat trout
(Oncorhynchus clarki), brown trout (Salmo trutta),
brook trout (Salvelinus fontinales), northern pike
(Esox lucius), and walleye (Stizostedion vitreum).
One agency, the Alaska Department of Fish and
Game, has even imposed a moratorium on
electrofishing in waters containing large rainbow

trout (Holmes et al. 1990; Reynolds pers. commun.).
Concern for similar injury to other species,
particularly endangered fishes in the Lower Colorado
River Basin, was the motivation for this review of
electrofishing impacts on fish.
Electrofishing has been one of the more effective
and consistently used methods of fish collection in
the Glen Canyon Environmental Studies (GCES)
program. However, as a result of the controversy
generated by Sharber and Carothers' (1988)
publication, which was based on work in Glen
Canyon National Recreation Area and Grand Canyon
National Park, the Aquatic Coordination Team of the
GCES and regional offices of the National Park
Service and Bureau of Reclamation are concerned
about the continued use of electrofishing to capture
and monitor endangered and other native fishes such
as the humpback chub (Gila cypha). The National
Park Service is mandated by law to preserve and
protect species found within its jurisdiction. It is
particularly concemed that extensive electrofishing of
spawning aggregations of humpback chub might
significantly impact reproduction and survival of the
population. Until these concerns are resolved, the
Superintendent of Grand Canyon National Park, J. H.
Davis, has suggested that electrofishing in Glen
Canyon National Recreation Area and Grand Canyon
National Park be kept to a minimum and used in
such a way as to minimize possible stress and injury
to humpback chub (memorandum to GCES program
manager, July 12 1990).
The National Park Service needs information to
fully evaluate impacts of electrofishing on humpback
chub for Section 7 consultation (Endangered Species
Act of 1973 and subsequent amendments). Once the
nature and degree of electrofishing impacts are
identified, it may be necessary to modify
electrofishing techniques or limit their application to
minimize the problem of physical injury.
Altematives to electrofishing may need to be
considered. The Bureau of Reclamation has
suggested three phases for acquisition of the needed
information. Phase I would be a position paper
consisting of a comprehensive literature review and
synthesis of existing information on effects of
electrofishing and means for reducing adverse
impacts. This information would be used to help