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

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MESA AND SCHRECK
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FIGURE 1.-Percentages of electrofished and marked cutthroat trout exhibiting normal or abnormal behavior at
various times after release in 10 sections (one section used twice) of Mill Creek, Oregon. Numbers in parentheses
are the number of marked fish released at each site. Graphs with only one plot indicate that no abnormal fish were
observed.
Wallis one-way analysis by ranks (Sokal and Rohlf
1981).
Results
Natural Stream Observations
When returned to the stream after they were
shocked and marked, cutthroat trout tended to
immediately seek cover, lie motionless on the
stream bottom, and not feed. The fish were gen-
erally lethargic and easily approached by a diver.
This behavior was observed in all sections and
persisted for various periods. Normally behaving
cutthroat trout swam actively, fed, reacted to the
presence of a diver, and interacted socially with
conspecifics. Immediately after release, the per-
(11) (6)
?o

o--oNORMAL FISH
e--&ABNORMAL FISH
centage of abnormal fish in several sections was
high. Generally, increasing numbers of fish re-
sumed normal activity as time progressed (Figure
1). The response time for marked fish to return to
normal behavior was highly variable among sec-
tions, and we were rarely able to account for 100%
of the marked fish after release. The percentage of
normal and abnormal fish and of marked fish not
observed for all sections combined is shown in
Figure 2A. We also combined data from sections
in which either more than nine or nine or fewer
marked fish were released; nine was the overall
mean catch of all sections (Figure 213, Q. Recov-
ery was faster in fish from sections where many
fish were captured than in those sections where