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

656
MESA AND SCHRECK
of these fish averaged about 10 min versus about
15 s for those that were only shocked. Indeed,
cortisol concentrations in fish 15 min after a single
electroshock did not differ significantly from
time-0 fish subjected to electroshock and marking.
Studies of the effects of repetitive electroshock-
ing on fish have shown reduced growth (Gatz et
al. 1986; Gatz and Adams 1987) and mortality
that was induced in a predictable manner in fish
populations (Saul 1980). However, the time in-
tervals between successive electroshocking treat-
ments in these studies were large relative to what
might be considered standard protocol for deter-
mining depletion-based population estimates
(Bohlin and Sundstrom 1977; Peterson and Ce-
derholm 1984). Our information provides insight
into stress responses of fish that are subjected to
multiple electroshocks in a stream but not cap-
tured. Such fish may be more common than might
be expected, especially in areas with much in-
stream cover.
For cutthroat trout receiving multiple electro-
shocks, cortisol was not liberated cumulatively, at
least not in the manner reported by Barton et al.
(1986) for healthy chinook salmon Oncorhynchus
tshawytscha subjected to acute multiple-handling
experiences. However, a cumulative effect may be
manifested in the secondary stress response, as
evident from the relatively long recovery periods
of lactate concentration in fish receiving multiple
electroshocks. We surmise that the severity of the
shocking stress was sufficient to produce a maxi-
mal response and that no capacity was left in the
interrenal tissue to elevate cortisol further after
subsequent shockings. However, Strange et al.
(1977) noted that plasma concentration ofcortisol
is a function of secretion and clearance; therefore,
the lack of a further increase in cortisol after the
third shock may have been due to an increased
clearance rate. As judged by the magnitude of the
maximum change, the response of lactic acid to
multiple electroshocks was greater than that to a
single shock, shocking plus marking, or a single
handling. Although lactic acid concentrations for
cutthroat trout receiving a single electroshock were
higher than values reported by Schreck et al. (1976)
for shocked rainbow trout, the pattern of recovery
was similar to that noted by Black et al. (1959)
and Schreck et al. (1976) for rainbow trout and
Burns and Lantz (1978) for largemouth bass Mi-
cropterus salmoides.
Fish receiving multiple electroshocks main-
tained elevated lactate concentrations for 6 h. This
period may be critical to the health of the fish
because it apparently reflects the period of anaer-
obic muscular activity (i.e., severe exercise: Schreck
et al. 1976). Although the proximate cause of death
of severely exercised fish is not known (Wood et
al. 1983), high concentrations of blood lactic acid
may contribute to mortality (Black 1958; Parker
and Black 1959). Whether high lactic acid con-
centrations in fish returned to a stream contribute
to mortality of those fish may depend on envi-
ronmental factors, such as temperature (Dean and
Goodnight 1964), or on the individual fish be-
cause it has been suggested that there is consid-
erable variation in susceptibility to increased blood
lactic acid (Caillouet 1967). Indeed, individual fish
variability, coupled with disturbance to the tanks
caused by periodic sampling, may explain differ-
ences between trials in both experiments and vari-
able lactic acid concentrations in control fish.
Recovery from the stresses of shocking and
marking, as judged from behavioral observations
at both Mill Creek and the artificial stream, are
generally supported by the recovery characteris-
tics of the physiological systems. A recovery pe-
riod of 3--6 h after release of marked fish seems
to be a reasonable assumption. To provide some
insight into the relation between behavior and
physiology, we correlated feeding and aggression
rates of wild and hatchery fish from our artificial
stream experiments with cortisol concentrations
from our physiological experiments. There was an
inverse relation between both feeding (r = -0.77)
and aggression (r = -0.57) rates and cortisol con-
centrations, which makes intuitive sense: when a
fish "feels" well physiologically, this should be ap-
parent externally in the form of normal behavior.
However, because of the behavioral changes ob-
served in Mill Creek fish and the longer recovery
period required for wild fish in the artificial stream,
the 3-6-h period of recovery may be an under-
estimate for applied field situations.
In conclusion, the procedures commonly used
to estimate fish population size subject fish to con-
siderable physiological stress and alter the normal
behavior of stream-dwelling cutthroat trout. Be-
cause these responses were highly variable and
generally lasted for several hours in our study, the
likely consequences are that some assumptions of
population size estimators may be invalid. Schreck
et al. (1976) found that rainbow trout failed to
recover from electroshock within the span of a
working day; therefore, they questioned whether
the assumption of equal vulnerability is met in
mark-recapture estimates if fish are marked, re-
leased, and recaptured on the same day. Our find-