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 649
100 A = ]NORMAL TABLE 2. -Summary ofcounts ofcutthroat trout made
®ABNORMAL by divers and of electrofishing catches when the deple-
80 =NOT OBS6Pt D tion method was used at Mill Creek in 1988. Fish counts
were made before each electrofishing pass and are shown
60 as the mean of counts by two divers. NA = not available.
40
Diver counts of fish Electrofishing
Stream Out of Pass
section In cover cover number Catch
20
0
100
j 80
O
'- 60
w
Y 40
0 20
F-
z 0
W
00100
W
a.
8060
40
20
0
U I [ s 4 5 6 24 168
TIME (h)
FIGURE 2.-Percentages of electrofished and marked
cutthroat trout with normal or abnormal behavior or
not observed at various times after release in Mill Creek.
Bars are (A) the percentages based on data from all sec-
tions combined, (B) mean percentages for fish in sections
where more than nine marked fish were released, and
(C) mean percentages for fish in sections where nine or
fewer marked fish were released.
fewer fish were caught. There was generally a higher
percentage of marked cutthroat trout unaccounted
for in sections where few fish were captured ini-
tially. The behavioral responses of marked fish
upon release included rapid swimming to large
rocks for cover (48% of the marked fish released),
lying motionless on the stream bottom (17%),
swimming to a large group of conspecifics (16%),
remaining in the water column (15%), or swim-
ming to undercut banks, root wads, or other debris
for cover (4%).
1 1 13 1 8
2 0 2 5
0 0 3 NA
2 5 43 1 10
4 33 2 12
2 24 3 5
5 2 25 1 18
2 19 2 13
2 12 3 9
,
7 2 7 1 13
0 1 2 3
NA NA 3 NA
9 5 12 1 13
1 4 2 8
1 3 3 0
Using a multiple-electroshock protocol, we ob-
served little change in the normal behavior of fish
remaining in the stream section after successive
electrofishing passes. During most dives, we found
the fish in the open and behaving normally; thus,
the disturbance did not appear to elicit a signifi-
cant fright or hiding response (Table 2). In only
one instance (two fish in section 1) were uncap-
tured fish found in heavy cover and behaving le-
thargically after the first electrofishing pass.
Artificial Stream Observations
In the artificial stream, there were no differences
between hatchery and wild fish in grand mean rates
of feeding (hatchery mean = 9.9 bites - fish-' - min-',
N = 19; wild mean = 11.0, N = 12) and aggression
(hatchery mean = 0.76 aggressive acts elicited-
fish-'-min-'; wild mean = 0.48) before electro-
shocking and marking. Relative to the grand mean
rate, hatchery fish fed at a significantly lower rate
1 h after release but fed normally at all other times
(Figure 3). The aggression rate of hatchery fish
after release was variable and was significantly
lower than the preshock mean rate at 1, 2, 5, 6,
and 30 h postshock (Figure 3). Mean rates of feed-
ing and aggression by wild fish decreased signifi-
cantly after shocking and marking; feeding rates
were significantly lower at all times (except 4 h
posttreatment) before returning to normal by 24
h posttreatment; however, aggression rates did not