9491

• UCREFRP Catalog Number: 9491
• Author: Snyder, D. E.
• Title: Electrofishing and Its Harmful Effects on Fish.
• USFW Year: 2003.
• USFW - Doc Type: Denver.
• Copyright Material: NO

SNYDER 5

Fig. 2. Brands (bruises or dark pigmental discolorations) in rainbow trout (Oncorhynchus mykiss) caused by
elec1trofishing. (Brands are usually temporary external manifestations of spinal injury, but injured fish often lack brands.
Photograph provided by and reproduced with permission ofW.A. Fredenberg, Montana Department ofFish, Wildlife,
and Parks.)

Since Sharber and Carothers' (1988, 1990) report of
substantial numbers of spinal injuries among electrofished
rainbow trout, some agencies have begun to verifY and
further investigate the extent, conditions, and causes of
electrofishing-induced spinal injuries (e.g., Holmes et aI.,
1990; Wyoming Game and Fish Department, 1990, 1991;
Fredenberg, 1992; Sharber et aI., 1994; others cited in the
introduction). As a result, one agency, the Alaska De-
partment of Fish and Game, imposed a moratorium on
electrofishing in waters containing large rainbow trout
(Holmes et aI., 1990). Similarly, the Montana Department
ofFish, Wildlife, and Parks (1994) issued regulations de-
signed to limit injuries to fish, including restricted use of
PDC over 30 Hz, and federal biologists in Idaho were
discouraged from using any electrofishing techniques
for capture of bull trout (Schill and Beland, 1995).
Many biologists across the continent and abroad
now acknowledge that potential incidence of
electro fishing injuries in otherwise normal-appearing
specimens might be a serious concern, at least for some
environmental conditions, equipment, and species. They
have been asking: what species and size groups are af-
fected, to what degree are they affected, what equipment,
electrical parameters, and techniques are responsible, what
specific mechanisms are involved, and what can be done
to eliminate or minimize the problems?
Most of these questions are not new. Spinal injury
has been associated with AC fields for over half a century
(e.g., Hauck, 1949), but until the late 1980's, it had been
largely overlooked as a significant problem with at least
some forms ofPDC. This perception endured despite only
limited documentation of injuries caused by AC and some

early publications documenting high incidence of injury
with PDC (e.g., Horak and Klein, 1967).
Despite electrofishing's prominent role in fishery re-
search and management, well-designed investigations to
address many of these questions and to understand the
genera] reactions of fish in electric fields are relatively
few, often very limited in scope (frequently a by-product
of another investigation), and difficult to compare be-
cause of differing objectives, gear, techniques, environ-
mental conditions, species, and terminology. With regard
to terminology, many researchers and authors fail to make
critical distinctions between PDC and continuous,
nonpulsed, direct current (DC), peak and mean output
voltages or field-intensity values, or narcosis and tetany.
Also, many reports of adverse effects are anecdotal or
lack critical data on the circumstances of the observa-
tions or experiments. Perhaps as a result of these limita-
tions, inconsistencies, and deficiencies, reported results
sometimes seem so contradictory that they appear to fo]-
low the law of physics which states that for every action
(report) there is an equal and opposite reaction (counter
report).
Broader questions also continue to be considered.
Biologists are concerned about potential effects of
e]ectrofishing on the survival, growth, reproduction, and
genera] well-being of populations and communities. Horak
and Klein (1967), Spencer (1967a), Hudy (1985), and
Schneider (1992) reported that e]ectrofishing injuries of-
ten heal and are not necessarily ]ethal or debilitating to
fish. Although most fish apparently survive
electrofishing-induced spinal injuries, Lamarque (1990)
stated that growth certainly would be impaired. Sharber