7706

• UCREFRP Catalog Number: 7706
• Author: Mesa, M. G. and C. B. Schreck
• Title: Electrofishing mark-recapture and depletion methodologies evoke behavioral and physiological changes in cutthroat trout
• USFW Year: 1989
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

Transactions of the American Fisheries Society l 18:644-658, 1989
e 770
Electrofishing Mark-Recapture and Depletion Methodologies
Evoke Behavioral and Physiological Changes
in Cutthroat Trout
MATTHEW G. MESA' AND CARL B. SCHRECK
U.S. Fish and Wildlife Service, Oregon Cooperative Fishery Research Unite
Department of Fisheries and Wildlife, Oregon State University
Corvallis, Oregon 97331, USA
Abstract. -We examined the behavioral and physiological responses of wild and hatchery-reared
cutthroat trout Oncorhynchus clarki subjected to a single electroshock, electroshock plus marking,
and multiple electroshocks in natural and artificial streams. In a natural stream, cutthroat trout
released after capture by electrofishing and marking showed distinct behavioral changes: fish im-
mediately sought cover, remained relatively inactive, did not feed, and were easily approached by
a diver. An average of 3-4 h was required for 50% of the fish to return to a seemingly normal
mode of behavior, although responses varied widely among collection sites. Using the depletion
method, we observed little change in normal behavior of fish remaining in the stream section (i.e.,
uncaptured fish) after successive passes with electrofishing gear. In an artificial stream, hatchery-
reared and wild cutthroat trout immediately decreased their rates of feeding and aggression after
they were electroshocked and marked. Hatchery fish generally recovered in 2-3 h; wild fish required
at least 24 h to recover. Analysis of feeding and aggression data by hierarchical rank revealed no
distinct recovery trends among hatchery fish of different ranks; among wild cutthroat trout, how-
ever, socially dominant fish seemed to recover faster than intermediate and subordinate fish.
Physiological indicators of stress (plasma cortisol and blood lactic acid) increased significantly in
cutthroat trout subjected to electroshock plus marking or single or multiple electroshocks. As
judged by the magnitude of the greatest change in cortisol and lactate, multiple electroshocks
elicited the most severe stress response; however, plasma concentrations of both substances had
returned to unstressed control levels by 6 h after treatment. It was evident that electrofishing and
the procedures involved with estimating fish population size elicited a general stress response that
was manifested not only physiologically but also behaviorally. These responses may affect the
accuracy of population size estimates by violating key assumptions of the methods, especially the
assumption of equal catchability of fish.
Because electrofishing is widely used to collect
fish for various purposes, the effects of electricity
on fish have received much attention. The phys-
iological effects of electricity on fish include a va-
riety of sublethal changes in blood chemistry that
last for various lengths of time (Schreck et al. 1976;
Bouck et al. 1978; van Waarde and Kesbeke 1983).
Morphological effects include physical injury and
sometimes death; however, many studies of the
lethality or incidence of injury due to electroshock
have been conducted in unnatural situations and
often under severe electrical conditions (Spencer
1967; Whaley et al. 1978; Hudy 1985). Studies of
the effects of electricity on fish behavior have con-
' Present address: U.S. Fish and Wildlife Service, Co-
lumbia River Field Station, Star Route, Cook, Wash-
ington 98605, USA.
2 Cooperators are Oregon State University, Oregon
Department of Fish and Wildlife, and U.S. Fish and
Wildlife Service.
centrated mainly on galvanotaxic and electronar-
cotic aspects (Taylor et al. 1957; Vibert 1963; Ba-
layev 1981).
Knowledge of the effects of electricity on fish is
important because electrofishing is commonly used
to estimate fish population size. Underlying all
mark-recapture or depletion estimators are as-
sumptions that, if violated, can affect the accuracy
of estimates (Gatz and Loar 1988). Of particular
importance is the assumption that marked and
unmarked fish are equally catchable, which has
been the subject of much statistical investigation
(Otis et al. 1978; Burnham and Overton 1979;
Seber 1982). The failure of this assumption has
been reported to affect the accuracy of fish pop-
ulation estimates (Cross and Stott 1975; Bohlin
and Sundstrom 1977; Peterson and Cederholm
1984). If it is assumed that fish must show normal
behavior and physiology to meet the assumption
of equal catchability, an understanding of the ef-
fects of procedures such as electroshocking, han-
dling, and marking on physiology and behavior
644