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

BEHAVIOR AND PHYSIOLOGY OF MARKED FISH 653
40so n-n electroshock+marking
•- -• single electroshock
o• • •O control
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24 168
TIME (h)
FIGURE 6.-Mean plasma lactic acid concentrations in unstressed (control) Alsea Hatchery cutthroat trout and
in fish subjected to a single 4-s, 300-V-DC electroshock or electroshock plus marking. Upper and lower panels
represent first and second replicate trials, respectively. Means (N = 5) within a time interval with no letters in
common are significantly different (P < 0.05); time intervals with no letters shown indicate no significant difference
among the means. Vertical bars represent 1 SE.
might alter catchability (e.g., Saul 1980) and sug-
gests that habitat quality is an important variable
to consider when conducting population esti-
mates. Electrofishing might be inefficient in areas
with much instream cover, and another technique
(e.g., estimates by snorkeling) may be more effec-
tive. Evidence for changes in catchability of
marked fish during subsequent electrofishing at-
tempts is equivocal (Cross and Stott 1975; Bohlin
and Sundstrom 1977; Yundt 1983; Peterson and
Cederholm 1984). Given our findings, this effect
of electrofishing needs further investigation.
Fish seemed to recover faster in sections with a
relatively large catch. These sections also had a
relatively low percentage of marked fish unac-
counted for and were areas where cutthroat trout
were found in large groups in deep water. Marked
fish often returned to such groups soon after re-
lease and were classified as normal fish even though
they might still have been affected by the stress
and were actually seeking refuge. Section differ-
ences in the amount and type of available cover
may have affected the observation of marked fish.
In areas with deep water and cobble and boulder
substrates, it was difficult to maintain position to
observe any fish that might have been hiding. Dim
light within large boulder complexes and around
undercut banks added to the difficulty of observ-
ing fish using such areas for shelter.
The general lethargy and cover-seeking re-
sponse of fish in the artificial stream were consis-
tent with observations at Mill Creek, especially