Hydrobiologia 371/372: 233–240, 1998.
J.-P. Lagardère, M.-L. Bégout Anras & G. Claireaux (eds), Advances in Invertebrates and Fish Telemetry.
© 1998 Kluwer Academic Publishers. Printed in Belgium.
233
Remote monitoring of heart rate as a measure of recovery in angled
Atlantic salmon, Salmo salar (L.)
W. G. Anderson1 , R. Booth1 , T. A. Beddow1 , R. S. McKinley1∗, B. Finstad2 , F. Økland2 &
D. Scruton3
1
Waterloo Biotelemetry Institute, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1
Norwegian Institute for Nature Research, Trondheim, Norway
3 Department of Fisheries and Oceans, St. John’s, Newfoundland, Canada
∗ Author to whom correspondence should be sent: E-mail: rsmckinle@sciborg.uwaterloo.ca
2
Key words: catch and release, heart rate, telemetry, angle, recovery
Abstract
The introduction of ‘Catch and Release’ fishery programs are now widely employed by fisheries managers in most
Atlantic Provinces, primarily due to the recent decline of Atlantic salmon stocks on the east coast of Canada.
However, there is still considerable debate among special interest groups and regulators as to the effectiveness of
the technique. Heart rate telemetry has been utilized as a tool for the assessment of metabolic rate in wild fish
by a number of investigators, and was employed in the present study in order to assess recovery following staged
angling events in Atlantic salmon. Wild Atlantic salmon were successfully angled at 20 ± 2 ◦ C and 16.5 ± 1 ◦ C
at Noel Paul’s Brook, Newfoundland. In addition, hatchery reared Atlantic salmon were angled at the Ontario
Ministry of Agriculture and Fisheries Research Station, Alma, Ontario, at a temperature of 8 ± 1 ◦ C. Survival rate
for the angled salmon was 20% at 20 ± 2 ◦ C; 100% at 16.5 ± 1 ◦ C; and 100% at 8 ± 1 ◦ C. Mean resting heart rate
for the fish angled at 16.5 ◦ C and 20 ◦ C was approximately 1.6 and 1.8 times greater than that of fish angled at
8 ◦ C. Heart rate, post angling, was found to increase 1.2 fold in the 8 ◦ C group, 1.3 fold in the 16.5 ◦ C group and
approximately 1.15 fold in the 20 ◦ C group. Time to recovery was assessed as a return to observed resting heart rate
for each individual fish and was found to be similar for both the 8 ◦ C and 16.5 ◦ C angled groups (approximately
16 h). Although heart rate telemetry in fish is, perhaps, not an ideal measure of metabolic rate, the present study
has demonstrated that remote monitoring of heart rate is a good indicator of post exercise physiological activity.
Introduction
Recent declines in the numbers of Atlantic salmon
on the east coast of Canada have prompted federal
and provincial governments to impose strict regulations on commercial and recreational fishing activities.
One measure employed was the introduction of year
round ‘Catch and Release’ fishery programs that are
now widely used throughout most Atlantic Provinces.
Although many fishery managers now practice catch
and release, there is still considerable debate among
special interest groups and regulators as to the effectiveness of the technique. Differences in opinion are
largely focused on the limited knowledge available
regarding post release survival rates and biological effects of angling on Atlantic salmon. As the importance
in using catch and release programs as a management
tool grows, particularly in Atlantic salmon sports fisheries, there is a greater need to understand how angling
and releasing wild fish influences the recovery of the
species.
Previous studies involving measurements of acidbase and metabolic disturbances have greatly assisted
in our current understanding of the effects of angling
on salmon physiology (Booth et al., 1995; Wilkie
et al., 1996). These studies have validated laboratory findings concerned with acid-base and metabolic
Article: hy-jl9 Pips nr. 165492 (hydrkap:bio2fam) v.1.1
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234
disturbances in exhaustively exercised fish, such as
glycogen store depletion and increases in muscular
lactate levels (Wood et al., 1983; Milligan & Wood,
1986). However, they have also raised important management questions with regards to optimal times for
the implementation of catch and release programs,
with temperature appearing to exert a major influence
on the survivability of angled and released salmon.
The development of physiological telemetry techniques has enabled researchers to investigate and
corroborate results previously reported in laboratory
based studies. Using telemetry devices which measure physiological processes such as EMG activity
(Kaseloo et al., 1992), and tailbeat frequency (Johnstone et al., 1992) researchers have attempted to correlate these physiological processes with metabolic rate
and thus an estimation of energy consumption and fish
activity. However, both these processes require the fish
to swim and after exhaustive exercise, such as an angling event, the fish will typically remain motionless
until such time when oxygen debt is repaid.
Heart rate telemetry has been utilized as a tool
for the assessment of metabolic rate in wild fish by a
number of investigators (Priede & Tytler, 1977; Armstrong, 1986; Lucas et al., 1991), with the correlation
proving to be good in northern pike, Esox lucius,
(Armstrong, 1986) but not as close in more aerobically active fish such as rainbow trout (Priede & Tytler,
1977). Although Thorarensen et al. (1996) recently
demonstrated the drawbacks in using heart rate in fish
as the sole indicator of metabolic rate, at the present
moment, remote assessment of heart rate is by far the
best indicator of physiological activity post exercise.
The present study utilised heart rate telemetry as
a means of obtaining in situ measurements of activity
during angling of Atlantic salmon, Salmo salar, and
monitoring recovery following release.
Materials and methods
Staged angling events were carried out on wild Atlantic salmon grilse, at Noel Paul’s Brook on the
Exploits river system in Newfoundland in August of
1996. Ambient water temperature was found to vary
greatly during the study period with a maximum temperature of 22 ◦ C at the beginning, dropping to 16 ◦ C
towards the end of the study period. A total of 20
fish were used in the study in Newfoundland. Due to
the nature of the physiological parameter being measured (see below) not all fish were found to exhibit
a constant obtainable signal. However, a total of 10
fish were implanted with heart rate tags (Lotek Eng.
Newmarket, Ont.) at Noel Paul’s Brook and successfully angled. These fish were grouped into two main
categories due to the varying temperature at the time
of testing; 5 fish (3 males and 2 females) successfully angled at 20 ± 2 ◦ C (mean weight 1723 ± 282 g,
mean fork length 58.8 ± 4.1 cm), and 5 fish (2 females 3 males) successfully angled at 16.5 ± 1 ◦ C
(mean weight 1295.6 ± 79.6 g, mean fork length
54.4 ± 1.2 cm). Staged angling events for hatchery
reared Atlantic salmon were carried out at the Ontario
Ministry of Agriculture and Fisheries Research station
in Alma, Ontario in September 1996. Temperature at
the fish hatchery during the study period was 8 ± 1 ◦ C.
A total of 6 fish (3 females, 3 males) were angled at
the hatchery (mean weight 2888 ± 185 g, mean fork
length 61.33 ± 1.1 cm).
Due to the nature of the pool where the wild fish
were angled, the potential was there for these fish to
escape into the Exploits river system. Consequently,
an anaesthesia that would produce sufficient calmness
for a 10–15 min surgical operation and did not demand
an extensive withdrawal period post-release, such as
MS-222, was required. The natural anaesthetic Clove
oil (Anderson et al., 1997), at a concentration of 40 mg
l−1 , was used to induce anaesthesia. Once a sufficient
depth of anaesthesia was deemed to have been reached
the fish were transferred to a foam bed where a fresh
solution of well aerated clove oil (30 mg l−1 ) was irrigated across the gills for the duration of surgery. The
heart rate transmitters used in the present study were
18 g in air (8 g in water) and 5 × 1.6 cm (LOTEK Eng.
Newmarket, Ontario). Each tag was cleaned in ethanol
prior to insertion, allowed to airdry, and gold tips were
attached to the end of each electrode to aid in electrical
contact and anchorage within the pericardial cavity.
A small incision was made on the ventral surface
of the fish (approx. 2 cm) and the body of the tag was
inserted within the abdominal cavity with the trailing
antenna brought out through a small puncture wound
on the ventro-lateral side of the fish. The electrode
wires were brought through the anterior end of the
wound, subcutaneously, towards the pectoral fins. The
gold tips were placed on specially designed surgical
probes and positioned within the pericardial cavity
through small holes in the lepidotrichs bone of the
pectoral girdle (Harder, 1975). Due to the nature of
the physiological process being measured, constant
contact with the heart was necessary to ensure a consistent signal from the transmitter. As a consequence,
hy-jl9.tex; 3/09/1998; 20:04; p.2
235
those fish which gave a constant signal during the operating procedure did not always provide a constant
signal once recovered, particularly during periods of
high activity such as angling. In an effort to reduce
this, the electrode wires leading from the pericardial
cavity to the abdominal cavity were tightly secured
onto the ventral surface of the fish, with enough slack
to allow for free movement of the electrode wires with
the movement of the fish. An autopsy was also carried out on each individual post experiment to ensure
the electrodes were still positioned appropriately. The
abdominal incision was closed with 4–6 sutures and
a button tag was sutured anterior to the dorsal fin
for future identification. The fish was then removed
from the operating table and placed in a recovery tank
(2 m × 1 m × 0.5 m) filled with fresh aerated river
water at ambient temperature. All fish were allowed
a minimum of three days in the recovery tank prior
to the angling event. Resting heart rate was recorded
between 48 and 72 h post surgery.
The angling events in Noel Paul’s Brook were carried out in a controlled channel (25 × 5 × 1 m) at
Noel Paul’s Brook adjacent to the station. For each
individual angling event, fish were removed from the
recovery tank, placed in a cooler of fresh aerated water, transferred to the channel, manually hooked (#8)
in the upper jaw and released. The fish were then angled to exhaustion on an 1.8 m graphite fly rod using
7 weight line and a 10 weight tippet. Exhaustion was
deemed to have been reached when the fish no longer
responded to the angler. Upon exhaustion the fish were
released from the hook and immediately released into
the angling pool. Heart rate of these fish was recorded
as soon as the fish was manually hooked and released
into the channel using a SRX_400 telemetry receiver
fitted with W20 firmware (LOTEK Eng. Newmarket Ontario). Post angling heart rate was continually
recorded for a minimum of 3 h and up to 16 h where
possible. Hatchery reared fish at the Alma Research
Station were operated on, hooked and angled in a
similar fashion as those in Newfoundland except that
the hatchery reared fish were angled in a large 10 m
diameter by 1.5 m deep circular tank.
Results
Analysis of the heart rate data has concentrated on
the angling period and the following recovery period
(Figures 1, 2 and 3). Each value presented in figures
1, 2 and 3 is a mean ± 1 SE and represents a mini-
mum sample size of 4. Although the 16.5 ◦ C fish were
angled for an average of 5.1 min, sufficient telemetry
data was not obtainable due to the intermittency of signal from the heart rate transmitters (particularly during
periods of high activity) and also the low angling times
in some of the fish. This also applies to the 20 and 8 ◦ C
groups, where angling times were an average of 11.8
and 8.1 min, respectively.
The mean resting heart rate of fish angled at
8 ± 1 ◦ C was 40 ± 0.28 beats per minute (bpm), and
ranged from 34.2 ± 0.5 bpm to 48.2 ± 0.5 bpm. Mean
resting values for the fish angled at 16.5 ± 1 ◦ C was
66.9 ± 0.5 bpm with a minimum of 54.8 ± 0.4 and
a maximum of 88.8 ± 1.3 bpm. Mean resting values for the fish angled at 20 ± 2 ◦ C was 72.3 ± 0.4
bpm, and ranged from 53.4 ± 1.81 bpm to 87 ± 1 bpm
(Figure 1).
Mean peak heart rate in the 8 ◦ C fish post angling
was 48.77 ± 0.7 bpm which occurred 2.5 h after the
event (Figure 2). Mean peak heart rate values in the
16.5 ± 1 ◦ C group was 90.68 ± 1.4 bpm 4 hrs after
angling (Figure 2). Heart rate in both the 16.5 and
8 ◦ C groups did not return to basal for as much as 16 h
(Figure 2). Due to the high mortality rates experienced
in the 20 ◦ C group sufficient numbers for the recording
of heart rate beyond 3 h was not obtainable. Mean
peak heart rate values in the 20 ± 2 ◦ C group was
83.54 ± 0.17 bpm 35 min after angling (Figure 3). Furthermore, heart rate of these fish during the three hour
observation period appeared to be very unpredictable.
One of the most striking initial findings of the
present study was the mortality rate of fish post angling. Of the five fish angled at 20 ± 2 ◦ C, only one
fish survived the following 72 hour post angling period. All the wild and hatchery reared salmon angled
at 16.5 ± 1 ◦ C and 8 ± 1 ◦ C respectively survived the
event and were in good condition when removed for
autopsy following the 72 h observation period. Interestingly, exhaustive states at 20, 16.5 ◦ C, and 8 ◦ C
were found to be visually very different. The 20 and
16.5 ◦ C fish at the end of the angling period were
found to be extremely docile and in some cases unable
to maintain equilibrium immediately post release from
the hook. However, the 8 ◦ C fish, although exhausted
to the extent that handling was not difficult, were still
able to maintain equilibrium and in some cases hold
station within the circular tank. These visual observations are reflected in the heart rate telemetry data,
whereby the heart rate between 1 and 4 min of angling in the 16.5 ◦ C group decreased from basal by a
factor of 1.4 (Figure 1). A similar decrease (factor of
hy-jl9.tex; 3/09/1998; 20:04; p.3
236
80
75
Heart Rate (bpm)
70
65
60
55
50
45
40
35
0
1
2
3
4
Angling time (min)
5
6
7
8
Figure 1. Change in heart rate of adult Atlantic salmon during angling at 3 distinct temperatures. Open circles = 16.5 ± 1 ◦ C; Open
squares = 20 ± 2 ◦ C; Closed circles = 8 ± 1 ◦ C. Values are expressed as a mean ± 1 SE.
1.3) from 1–8 min of angling in the 20 ◦ C group was
observed. However, heart rate increased by a factor of
1.16 over an 8 minute angling period of the 8 ◦ C group
(Figure 1).
Discussion
Results from the present study have demonstrated an
increase in resting values with an increase in temperature (Figure 1). Resting values of fish angled at 8 ◦ C
and 16.5 ◦ C increased by a factor of approximately
1.6, which increased further to a factor of 1.8 from 8
to 20 ◦ C. This is perhaps not surprising as heart rate in
fish has been shown to be closely related to changes in
temperature (Farrell & Jones, 1992) with the degree of
vagal tone perhaps being a major factor with changes
in temperature (Priede, 1974). Although, Gamperl et
al., (1994) demonstrated levels of catecholamines and
cortisol to remain elevated for up to six days postoperation, the present study used only a 48 h period
prior to the collection of basal heart rate data. This
was considered to be sufficient as previous studies using heart rate telemetry used a minimum of 24 h post
surgery before the onset of experimentation (Claireaux
et al., 1995; Lucas, 1994; Nelson et al., 1996). Furthermore, the results reported by Gamperl et al. (1994)
were from fish confined in ‘black box’ experiments.
The fish in the present study were allowed to recover
in an large (2 m × 1 m × 0.5 m) recovery tank.
Examination of heart rate during angling has
demonstrated a decrease in heart rate of the wild fish
angled at 20 and 16.5 ◦ C but an increase in heart rate
of the hatchery reared 8 ◦ C group. Visual observations during angling demonstrated that the wild fish
fought very well with the angler and would often use
anaerobic bursts in swimming in an effort to escape
from the line. The hatchery reared fish on the other
hand did not demonstrate a similar willingness to fight
to the extent that one fish had to be dragged through
the water to encourage it to struggle. Burst exercise
in fish has been reported to induce a bradycardia (decrease in heart rate) (Stevens et al., 1972; Farrell,
1982). This depression is considered to be necessary
to avoid hypertension as the violent contractions of
skeletal muscle close off the peripheral blood vessels
(Farrell & Jones, 1992). It is possible, therefore, that
the depression in heart rate in the wild fish is due to
the intense activity in these fish in comparison to the
hatchery reared fish at 8 ◦ C fish. Whether the reduction
hy-jl9.tex; 3/09/1998; 20:04; p.4
237
100
95
90
85
80
Heart rate (bpm)
75
70
65
Basal
60
55
50
45
40
Basal
35
30
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Recovery time (h)
Figure 2. Change in heart rate of adult Atlantic salmon during recovery from angling at two distinct temperatures. Open circles = 16.5 ± 1 ◦ C;
Closed circles = 8 ± 1 ◦ C. Values are expressed as a mean ± 1 SE.
90
Basal
85
80
Heart beat (bpm)
75
70
65
60
55
50
45
40
35
30
0
20
40
60
80
100
120
140
160
180
200
Recovery time (min)
Figure 3. Change in heart rate of adult Atlantic salmon during recovery from angling at 20± 2 ◦ . Values are expressed as a mean ± 1 SE.
hy-jl9.tex; 3/09/1998; 20:04; p.5
238
in activity of the 8 ◦ C fish was a function of temperature or their life history is hard to say. However, studies
investigating the swimming performance of wild and
hatchery reared Atlantic salmon smolts and parr have
produced conflicting results with regards to holding
ability and swimming performance, with the hatchery
reared fish generally having a lower performance than
their wild counterparts (Graham et al., 1996; Moore
et al., 1995; Peake & McKinley, 1997; Rimmer et al.,
1985).
Although trends in heart rate during angling of the
8 and 16.5 ◦ C groups varied considerably, the trend
in heart rate during recovery of these two groups did
not. Both groups demonstrated an increase in heart
rate post angling for up to 16 h. However, the elevation in heart rate above resting levels was greater
in the 16.5 ◦ C group than that observed in the 8 ◦ C
group. Maximal increase above basal during recovery
in the 8 ◦ C group was by a factor of 1.2 after 2.5 h,
whereas heart rate increased by a factor of 1.35 in the
16.5 ◦ C group 4 h after angling. Interestingly heart
rate peaked in Atlantic salmon recovering from forced
exercise within 30 min of the trial by factors of 1.2
and 1.3 for 8 and 18 ◦ C acclimated fish (Anderson,
unpublished data). The reasons for the discrepancies in
recovery times between the forced exercised fish and
the angled fish is unclear. However, the stressful event
of being hooked and angled will certainly have exacerbated any cardiovascular changes associated with
exhaustive exercise. This demonstrates the usefulness
of the heart rate transmitter in varifying and extending
our knowledge of the cardiovascular function in fish
post exercise.
Unfortunately extended recording of heart rate in
fish angled at 20 ◦ C was not possible due to the mortalities in this group. However, what is evident is that
the heart rate of these fish immediately after angling
and for the following 3 h followed an unusual trend.
Typically following exhaustive exercise, fish heart rate
increases (Farrell & Jones, 1992) and this is demonstrated in the present study for the 8 and 16.5 ◦ C fish.
However, immediately after angling the heart rate of
the 20 ◦ C group dropped below basal and remained
lower for up to 30 min. The reasons for this are unclear
but what is not known is changes in stroke volume
and ultimately cardiac output during this time. To
compensate the observed dramatic decrease in heart
rate following angling in this group (Figure 3), one
would expect an even bigger increase in stroke volume
to allow for an anticipated increase in cardiac output
following exhaustive exercise.
Success of catch and release obviously depends on
the survival rate of released salmon and, therefore,
the question of recovery rate and delayed mortality is
important. Delayed mortalities have been reported in
some exhaustively exercised and angled fish (Bouck
& Ball, 1966; Beggs et al., 1980; Graham et al.,
1982; Wood et al., 1983; Ferguson & Tufts, 1992), but
relatively low mortality has been reported for caught
and released wild Atlantic salmon (Booth et al., 1995;
Tufts et al., 1991). However, Wilkie et al. (1996) reported a mortality rate of 40% in their angled salmon,
a figure which is lower than the present study for fish
angled at high temperatures (80%) which may be a
function of the increased stress and temperature on
the fish implanted with a transmitter. However, zero
mortalities in both the 16.5 and 8 ◦ C angled groups
would indicate that an increase in temperature is the
critical factor regarding increases in the likelihood of
delayed post angling mortality. Although all the fish
angled at 16.5 ± 1 ◦ C survived the angling event, immediately post angling the fish were very docile and in
some cases were unable to maintain equilibrium. As
a consequence, if further excessive demand is placed
on the heart in response to a repeated stress in warmer
waters, these fish could have a reduced ability to adjust
cardiovascular parameters accordingly and, therefore,
increase the likelihood of mortality.
Heart rate during recovery in the fish angled at
20 ◦ C was very irregular, the reasons for which are
unknown but serve to underline the severe physiological imbalance these fish experience post angling.
The cardiovascular parameters in conjunction with
the reduction in metabolites (Wilkie et al., 1996) of
fish angled at higher temperatures could make them
more susceptible to disease, although this would occur over the longer term. Furthermore, fish angled at
these temperatures experience an energy loss which
could ultimately effect their ability to spawn and/or
defend nesting sites. Interestingly however, Booth et
al. (1995) demonstrated that fish angled in the late fall
(6 ◦ C) very close to the spawning season did not have
a reduction in spawning capacity when compared to
fish not angled and taken at the same time.
Catch and release programmes were employed by
fisheries managers in North America as a early as
1964 (Barnhart, 1989) as year round strategies, in
an effort to reduce depletion of fish stocks related
to overfishing in rivers and lakes. The suite of catch
and release studies carried out in New Brunswick,
Canada (Bielak, 1996; Booth et al., 1995; Wilkie et al.,
1996), in combination with the present study, demon-
hy-jl9.tex; 3/09/1998; 20:04; p.6
239
strate that catch and release may not be an effective
management strategy throughout the entire season.
Angling during the mid summer months when water
temperatures are close to and in excess of 20 ◦ C may
well induce a high percentage of delayed post angling
mortality. Unfortunately management decisions based
solely on changes in temperature would be difficult
to implement as prediction of river temperature is not
precise. Furthermore, the dynamic range of temperature throughout any given river system could vary
considerably. Consequently, a clearer understanding
of the environmental changes in individual watersheds
is warranted prior to the implementation of catch and
release management decisions based on temperature
alone.
Acknowledgements
Support for this work was provided by a grant from
the Canada/Newfoundland Cooperation Agreement on
Salmonid Enhancement and Conservation to RSM and
is greatly appreciated. The support from Rex Porter,
Department of Fisheries and Oceans, St. John’s, Newfoundland, and Richard Moccia of the Ontario Ministry of Agriculture and Fisheries Research Station in
Alma is gratefully acknowledged.
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