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North American Journal of Fisheries Management 24:617–623, 2004
© Copyright by the American Fisheries Society 2004
Effect of Hook Type on Mortality, Trauma, and Capture
Efficiency of Wild, Stream-Resident Trout Caught by
Active Baitfishing
R
OBERT B. DUBOIS*
Wisconsin Department of Natural Resources, Bureau of Integrated Science Services,
1401 Tower Avenue, Superior, Wisconsin 54880, USA
K
URT E. KUKLINSKI
Department of Wildlife Conservation, Fisheries Research Laboratory,
500 East Constellation, Norman, Oklahoma 73072, USA
Abstract.—We used an active fishing technique (tight-line fishing with immediate hook set) to
compare mortality, injury, and capture efficiency of wild, stream-resident salmonids captured by
barbed or barbless single hooks baited with leaf worms Lumbricus rubellus. Mortality at 72 h (2–
7%), anatomical hooking location (superficial or deep), and eye damage (5% of captures) in
brook trout Salvelinus fontinalis did not differ between hook types. However, brook trout that
were deeply hooked were more likely to die when barbed hooks were used. Mortality and eye
damage in brown trout Salmo trutta were similarly low, but sample sizes were insufficient for
comparison of hook types. Hook types did not differ significantly in terms of hooking efficiency,
frequency of fish escape after hooking, or the mean unhooking time in which fish were held out
of water. Active baitfishing resulted in levels of postrelease mortality that were substantially
lower than those commonly reported in baitfishing mortality studies.
Hooking studies of stream-dwelling salmonids
caught on live bait have reported a wide range of
postrelease mortality levels, from as low as 3% to well
over 60% (Westerman 1932; Thompson 1946; Shetter
and Allison 1955; Hunsacker et al. 1970; Warner
1976, 1979; Warner and Johnson 1978; Hulbert and
Engstrom-Heg 1980; Pauley and Thomas 1993; Schill
1996). In separate reviews, Wydoski (1977) offered a
widely applied average of 25% mortality when
salmonids are released from baited hooks, and
Mongillo (1984) concluded that a postrelease
baitfishing mortality of about 30% can be expected,
with a range from 20% to 50% depending on the
species of trout. Because these mortality levels are
substantially higher than the mean mortality usually
associated with flies or artificial lures (usually well
under 10%), regulatory agencies have often created
“artificials-only” sections within special-regulation
trout waters.
Carline et al. (1991) and Schill (1996) have chal-
lenged the use of these high mortality estimates in
management decisions, by presenting evidence that
baitfishing mortality under actual fishing conditions is
much lower, at least in some waters and with some
techniques. Schill (1996) also pointed out the need for
more information about the effects of baitfishing on
_____________
*
Corresponding author: robert.dubois @ dnr.state.wi.us
Received October 28, 2002; accepted September 2, 2003
salmonid populations and about certain techniques,
such as active baitfishing, that could reduce negative
effects. In active baitfishing, a tight line is maintained
between the rod tip and the bait, and the hook is set
when a strike is felt. The idea that the incidence of
deep hooking, and therefore mortality, of stream-
resident salmonid can be substantially reduced by
active baitfishing is intuitively logical and has some
empirical support (Schill 1996; Schisler and Bergersen
1996)
The use of barbless bait hooks to reduce post-release
mortality of salmonids has also been a topic of recent
debate. In a meta-analysis of salmonid hooking
mortality, Taylor and White (1992) concluded that the
use of barbed hooks caused higher mortality than the
use of barbless hooks during baitfishing. However,
other workers identified a flaw with this analysis, and
concluded from the same data set that no difference in
mortality between hook types was demonstrated
(Schill and Scarpella 1997; Turek and Brett 1997).
Responding to the criticisms, Taylor and White (1997)
called for more primary research, recognizing that the
number of existing trials of baited, barbless hooks was
small. Schill and Scarpella (1997) called for more
studies to compare bait-hook types, but argued from
existing data that barbed-hook restrictions represent a
social issue that is not biologically justified. Schill and
Scarpella (1997) also provided evidence that barbless
hooks do not greatly reduce the time needed for
618 DUBOIS AND KUKLINSKI
unhooking fish, but could reduce fishing quality by
causing anglers to lose more fish.
Our objectives were twofold: (1) to determine the
rates of mortality and eye damage in wild, stream-
resident brook trout Salvelinus fontinalis and brown
trout Salmo trutta caught with an active baitfishing
technique, and (2) to determine if mortality, eye
damage, anatomical hooking location, ease of release,
and capture efficiency differed between barbed and
barbless bait hooks.
Methods
We fished in a 250-m reach of the Little Brule
River, a western Lake Superior tributary situated in
Douglas County, Wisconsin. The reach is above a
low-head dam at the upper boundary of a state-
operated fish hatchery. Because of its proximity to the
hatchery, the study zone fell within a designated fish
refuge that was closed to public fishing. However, all
trout caught were wild fish. The study reach had a
mean width of 4.7 m and a mean depth of 0.5 m, and
ran through an open, marshy area with grasses and
sedges lining the banks. Most trout were caught from
several runs and small pools that collectively averaged
about 0.75 m in depth. Water velocities in these areas
ranged from 0.0 to 0.76 m/s and averaged 0.3 m/s.
Water temperatures on the sampling and holding days
ranged from 7.2°C to 17.2°C and averaged about
12°C.
We fished during the morning and early afternoon
of 10 trial days that spanned the general open season
for inland trout fishing in Wisconsin (first Saturday in
May through September): 29 June, 6 July, and 29
September 1998; 9 and 12 June and 16 and 22
September 1999; and 9, 18, and 31 May 2001. Four
experienced trout anglers used light-action spinning
gear with leaf worms Lumbricus rubellus as bait. No
effort was made to standardize the amount of time
each angler fished, and all anglers did not fish on all
trial days. Anglers used 4- or 6-lb test line, a small,
split shot for weight, and barbed or barbless baitholder
hooks (size 6). Hooks were made barbless by bending
down the terminal barbs (the baitholder barbs were left
intact). Fishing was done from shore or from a small
canoe. Anglers alternated hook types after every 6–8
trout captured to assure near-equal sample sizes.
All angling was “active,” with the line having little
or no slack once the bait was in the water. Thus,
anglers were able to feel a strike almost immediately
and set the hook as soon as the strike was felt. Anglers
were told that the goal was to simulate actual fishing
conditions and were instructed to play and handle fish
as they ordinarily would but without either “horsing”
them (i.e., reeling them in continuously and rapidly) or
playing them to exhaustion. Landing nets were used
when needed for larger fish, and forceps were used for
unhooking deeply hooked fish. Anglers were
instructed to cut the line at the snout whenever the
hook could not be removed without causing internal
damage (i.e., hooks in the gills or gullet).
A person accompanied each angler to record
unhooking time, anatomical hooking location,
occurrence of bleeding or eye damage, and total length
(TL) for each fish captured. Unhooking time began
when a fish was removed from the stream and ended
with placement of the fish into a water-filled bucket
after the angler removed the hook or cut the line. Each
trout was examined for evidence of eye injury (based
on criteria developed by DuBois and Dubielzig [2004,
this issue]) and jaw injury by gently turning the fish on
its side while it was submersed in the bucket. The fish
was then removed briefly from the water for TL
measurement to the nearest millimeter, and was given
minimal, tip-of-fin clips to indicate the type of hook
used, occurrence of trauma, and the anatomical
hooking location. Fish hooked in the gills, esophagus,
or stomach were classified as deeply hooked, whereas
those hooked in the jaws, tongue, roof or floor of the
mouth, or externally were classified as superficially
hooked. Examinations, fin clips, and measurements
were performed by the anglers, who were all fisheries
professionals. The amount of time each fish was held
out of water was usually less than 5 s.
For each hook type, we recorded the total number of
strikes, the number of strikes that were missed, and the
number of hooked fish that were lost by each angler.
From these data, we calculated hooking efficiency (the
proportion of strikes that resulted in hooked fish), the
proportion of hooked fish that escaped, and capture
efficiency (the proportion of strikes that resulted in
landed fish).
After recording the data, anglers placed the fish into
45-L, water-filled coolers with freshwater exchanged
every 10–30 min depending on the number and sizes
of fish in the cooler. When 10–15 fish had
accumulated in a cooler, they were transported to a
nearby instream live-cage for holding via the methods
of DuBois and Dubielzig (2004).
Bleeding was subjectively classified as slight or
substantial based on the amount of blood present
BAITFISHING MORTALITY OF WILD TROUT 619
TABLE 1.—Incidence of mortality, eye damage, and
bleeding among brook trout caught with barbed and barb-
less baited hooks in the Little Brule River, Wisconsin, during
1998, 1999, and 2001.
Hook type
and statistic
Number
caught
Mortality
at 72 h (%)
Severe eye
damage at
72 h (%)
Substantial
bleeding
when
caught (%)
Barbed 100 7 6 16
Barbless 99 2 5 14
Z-statistic 1.357 -0.024 0.177
P-value 0.175 0.980 0.860
when the fish was landed. Caveats about interpreting
blood loss of salmonids in hooking studies are
described by DuBois and Dubielzig (2004). Deaths
were noted at the time of capture and at 24, 48, and 72
h after capture; to minimize stress during the holding
period, fish were not handled or removed from the
water at either the 24- or 48-h checks. A 3-d holding
period was considered sufficient to estimate delayed
mortality, because at least 90% of hooking-related
mortality of salmonids occurs within 48 h of capture
(Mongillo 1984; Dedual 1996). Eye damage was
reassessed at the end of the holding period (72 h). Fish
were not fed during the holding period.
All statistical tests were performed in the SYSTAT
and SigmaStat statistical software packages (SPSS
1997) with the significance level α set at 0.05. We
used Z-tests (equivalent to chi-square tests when
comparing two proportions) to test null hypotheses
that the proportions of fish suffering mortality, eye
damage, and deep hooking were independent of hook
type. Anatomical hooking location, hooking
efficiency, hooked fish that escaped, and capture
efficiency were also expressed as proportions and
were compared between hook types by use of Z-tests.
Differences in mean unhooking time between hook
types and species were examined with Mann–Whitney
rank-sum tests because assumptions of normality were
violated in all comparisons.
Results
Anglers caught 267 salmonids during 40.5 angler-
hours of fishing on the 10 trial days, for a catch rate of
6.6 fish/angler-hour. Brook trout (n = 199) ranged in
length from 103 to 304 mm; brook trout caught on
barbed hooks averaged 198 mm, and those caught on
barbless hooks averaged 212 mm. Brown trout (n =
68) ranged in length from 144 to 526 mm, with means
of 244 mm for brown trout caught on barbed hooks
TABLE 2—Incidence and mortality of deeply hooked and
superficially hooked brook trout caught with barbed and
barbless baited hooks in the Little Brule River, Wisconsin,
during 1998, 1999, and 2001.
Superficially hooked Deeply hooked
Hook type
and statistic
Proportion
Mortality
(%)
Proportion
Mortality
(%)
Barbed 0.76 0.0 0.24 29
Barbless 0.67 0.0 0.33 6
Z-statistic 1.249 1.989
P-value 0.211 0.047
and 272 mm for those caught on barbless hooks.
Mortality at 72 h was low (2–7%) for both species
of trout, and did not differ significantly between hook
types for brook trout (Table 1). Mortality of brown
trout was 3% for each hook type, but because sample
sizes were small and there was only one death per
hook type, we did not test for hook-type effects on this
species. Anatomical hooking location was an
important factor in mortality, as 10 of the 11 fish that
died were hooked in a gill or in the stomach or
esophagus. Most deaths occurred within 1 h of
capture. One brown trout died after being snagged
externally in the belly. Mortality was 16% in brook
trout that were deeply hooked and 8% in brown trout
that were deeply hooked. Several deeply hooked brook
trout were bleeding copiously and could not
effectively maintain their equilibrium when landed,
yet they survived the holding period and appeared
vigorous at the time of release. These fish might not
have survived without the protection from predators
afforded by the cages during recovery.
Anatomical hooking locations in brook trout did not
differ significantly between hook types (Table 2):
most fish were hooked superficially in the jaw or in
the roof or floor of the mouth. However, deeply
hooked brook trout were more likely to die when
barbed hooks were used than when barbless hooks
were used (Table 2). For hook types and species
combined, 26% of hooking locations were deep, and
15% were deep enough to require the line to be cut at
the snout. Of the fish hooked in the stomach or
esophagus, all but one required the line to be cut. Of
the fish hooked in the gill area, less than a third
required cutting of the line.
When landed, 13% of salmonids either had obvious
eye damage or had the potential for such damage
based on hook placement. At 72 h, 5% of the catch
had persistent eye injuries that, based on the criteria of
620 DUBOIS AND KUKLINSKI
TABLE 3.—Strikes, hooking efficiency (proportion of strikes resulting in hooked fish), proportion of hooked fish escaping, and
capture efficiency (proportion of strikes resulting in captures) of brook trout and brown trout striking on barbed and barbless baited
hooks in the Little Brule River, Wisconsin, during 1998, 1999, and 2001.
Hook type
and statistic
Total number
of strikes
Hooking
efficiency
Proportion of hooked
trout that escaped
Capture
efficiency
Barbed 228 0.697 0.145 0.596
Barbless 234 0.726 0.229 0.568
Z-statistic 0.585 1.822 0.516
P-value 0.558 0.068 0.606
DuBois and Dubielzig (2004), were sufficient to result
in long-term visual impairment. The prevalence of
severe eye damage did not differ significantly between
hook types (Table 1). Seven fish with eye damage
when caught had clearly improved by 72 h. Overall,
15% of brook trout were bleeding substantially when
landed (Table 1). No jaw injuries were caused by
either hook type.
The mean amount of time that fish were held out of
water for unhooking (all anglers pooled) was not
significantly different (t = 6,936.5, P = 0.056) between
barbed hooks (22 s, n = 75) and barbless hooks (20 s,
n = 93). Unhooking time ranged from 6 to 120 s.
Unhooking times for fish that died averaged 22 s.
Capture efficiency, the proportion of hooked fish that
escaped, and hooking efficiency did not differ
significantly between hook types (Table 3).
Discussion
This study confirmed what many anglers have
suspected based on experience, that active fishing with
an immediate hook set reduces the time for baited
hooks to be deeply ingested by stream salmonids, and
thus reduces the risk of mortality compared to slack-
line fishing. Deep hooking causes most of the
mortality incurred by stream-dwelling salmonids
released by bait anglers (Wydoski 1977; Hulbert and
Engstrom-Heg 1980; Pauley and Thomas 1993; Schill
1996). For example, Hunsacker et al. (1970) observed
8% mortality when cutthroat trout Oncorhynchus
clarki were not deeply hooked compared to 73%
mortality when they were deeply hooked. Our rates of
deep hooking were fairly low (26% overall), and our
results are consistent with other baitfishing studies that
have documented low overall mortality when most
salmonids were not deeply hooked. Schill (1996)
reported significant differences in deep-hooking rates
between tight-line (12%) and slack-line (50%)
captures of wild, bait-caught rainbow trout O. mykiss.
He calculated an overall bait-hooking mortality
estimate of 16%, which included both tight-line and
slack-line captures. Thompson (1946) found low
hooking mortality (about 3%) of cultured salmonids
during worm fishing in clear water, where fish could
be seen taking the bait, and when the hook set was
immediate. Schisler and Bergersen (1996) found lower
deep-hooking rates and lower mortality rates when
scented, artificial baits were actively fished versus
passively fished. Warner (1976, 1979) also found low
mortality (between 5% and 6% in both studies) of
Atlantic salmon Salmo salar during worm fishing in a
hatchery; these fish took the bait gingerly and were
hooked as soon as they accepted the bait.
Our mortality estimates for deeply hooked, wild
brook trout (16%) and brown trout (8%) after line
cutting were at the low end of the published mortality
range associated with line cutting in similar studies.
Cutting of the line is known to dramatically improve
the survival of deeply hooked salmonids. Mortality of
deeply hooked, wild rainbow trout in Badger Creek,
Idaho, was 58% lower when the line was cut than
when the hook was removed (Schill 1996). Mason and
Hunt (1967) reported that, in deeply hooked, cultured
rainbow trout, mortality after 4 months was 34% when
the line was cut, whereas mortality averaged 89%
when the hook was removed either with the fingers
(95% mortality) or with long-nosed pliers (82%
mortality). Hulbert and Engstrom-Heg (1980)
observed 59% mortality of deeply hooked brown trout
after 4–5 months when the hook was removed and
18% mortality when the line was cut, but they noted
that other factors may have affected mortality during
the holding period. Hulbert and Engstrom-Heg (1980)
stated that overall short-term mortality would have
been about 7% (rather than 22%) if they had cut the
line on all deeply hooked fish. Schisler and Bergersen
(1996) reported 55% mortality of deeply hooked
salmonids when the hook was removed, compared to
21% mortality when the line was cut. Of deeply
hooked Atlantic salmon in a hatchery, 57% mortality
occurred when the line was cut versus 90% mortality
when the hooks were removed with long-nosed pliers
BAITFISHING MORTALITY OF WILD TROUT 621
(Warner 1979).
Our finding of no difference in mortality between
barbed and barbless hooks affirms the conclusion
given in several studies, that there is no biological
basis for barbed-hook restrictions for stream
salmonids (Thompson 1946; Hunsaker et al. 1970;
Falk et al. 1974; Dotson 1982; Titus and Vanicek
1988; review by Wydoski [1977]; meta-analysis by
Schill and Scarpella [1997]). In the only comparison
of barbed and barbless baited hooks for salmonids,
Westerman (1932) reported slightly higher mortality
of cultured brook trout caught on barbed hooks. In
their disputed meta-analysis of baitfishing mortality of
salmonids, Taylor and White (1992) compared
Westerman’s two barbless bait-hook trials with 23
barbed bait-hook trials from other studies (pooling a
variety of species and conditions) to arrive at
significantly different mean mortality between barbed
and barbless bait hooks. We have no explanation for
our finding of higher barbed-hook mortality of brook
trout when hook placement was deep, other than to
speculate that barbed hooks might have caused larger
wounds. The lack of difference in unhooking times
between the hook types is consistent with other
studies. In aggregate, these studies show that if a
difference in unhooking times between the hook types
exists, it is unlikely to be of sufficient duration to
affect survival (Falk et al. 1974; Schill and Scarpella
1997; DuBois and Dubielzig 2004). Because all fish
that were held out of water for longer than 30 s
survived the holding period, air exposure was not a
factor in the death of fish in our study. Use of barbless
hooks is widely believed to increase the proportions of
hooked fish that escape from anglers, but our results
for baited hooks do not support that notion. However,
in other studies of stream salmonids, the proportions
escaping were significantly higher for barbless
spinners (DuBois and Dubielzig 2004) and barbless
flies (Barnhart 1990) than for barbed varieties. In an
ocean troll fishery, Butler and Loeffel (1972) found
higher catch rates of coho salmon O. kisutch on barbed
hooks but no differences in chinook salmon catch rate
between hook types. Knutson (1987) also reported
equal efficiency of barbed and barbless hooks in the
landing of Pacific salmon Oncorhynchus spp. by
charter-boat anglers.
Although some studies have noted hooking-related
eye damage in salmonids, we are aware of only one
(DuBois and Dubielzig 2004) that identifies this
damage and rates its severity. That study reported
severe eye damage in about 10% of wild, stream-
dwelling salmonids caught on Mepps spinners. The
damage did not differ between single and treble hooks
or between barbed and barbless hooks. In our study,
the incidence of eye damage was similarly low (about
5% of the catch) and also did not differ between hook
types. No fish with eye damage died during the 72-h
observation period, and several cases of minor eye
injury improved over that short time frame. Although
most cases of fish eye damage are not immediately
lethal, long-term visual impairment from serious
hooking injuries may reduce survival by limiting the
fish’s ability to capture food, compete for territories,
and escape predators. However, the data are presently
insufficient to predict delayed mortality rates for eye-
damaged fish.
Accumulating evidence from other studies suggests
that baitfishing may have less negative impact on
wild, stream-resident salmonid fisheries than
previously thought, and our finding of low mortality
during active baitfishing may provide a partial
explanation. More research on the proportions of
anglers that actively baitfish under a variety of
conditions would be helpful. Additional research is
also needed on the effects of baitfishing on
populations and on the effect of multiple captures with
bait on long-term size structures. We stress that
restrictions on baitfishing should be supported by
evidence that biological gains will result. Otherwise,
restrictions unnecessarily reduce angling opportunities
during a period of stagnant or declining angling
license sales in most states (Sport Fishing and Boating
Partnership Council 1998; Duda et al. 1999). Bait-
fishing is popular with anglers. In 1997–1998, 73% of
all anglers (trout anglers included) fished with bait,
whereas only 14% of all anglers flyfished (Duda et al.
1999). By promoting active baitfishing, as well as
line-cutting of deeply hooked fish, fisheries managers
should be able to reduce bait-related mortality and
rates of deep hooking in the trout streams they
manage. Because hooking rates in our study were high
(mean = 69%), many baitfishers should respond
favorably to education about active fishing. Our
results generally support the idea that little biological
benefit results from barbed-hook restrictions on live-
bait fisheries. However, in fisheries where rates of
deep hooking are substantially higher than the rates we
measured, use of barbless hooks may reduce mortality.
Acknowledgments
This study was funded in part by the Wisconsin
Department of Natural Resources (WDNR). We thank
622 DUBOIS AND KUKLINSKI
N. Gruenies and T. Fratt for field assistance, and W.
Gobin and L. Nelson of the WDNR Brule Trout
Rearing Station for use of the rearing station facilities.
We also thank P. Rasmussen for assistance with data
analyses. Review comments from W. Blust, D. C.
Knickle, K. Gelwicks, J. Pleski, S. Toshner, and
several anonymous reviewers improved the
manuscript.
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