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Will Harbour porpoises (Phocoena phocoena) habituate to pingers?

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Large bycatches of harbour porpoises (Phocoena phocoena) occur in gillnet fisheries throughout the Northern Hemisphere. Several mitigation measures, including acoustic deterrent devices or 'pingers', have been used in efforts to reduce this bycatch. The potential exists for harbour porpoises to habituate to pingers, thus reducing their effectiveness over time. A field experiment was conducted to test the hypothesis that porpoises habituate to the sound produced by pingers. Porpoise echolocation and movements were monitored around a mooring equipped with a pinger (Dukane NetMark™ 1000) for three months in summer 1998 in the Bay of Fundy. Using a mean-shift model it was estimated that porpoises were initially displaced 208m from the pinger (p = 0.019), but this displacement diminished by 50% within four days (p = 0.019). Using a probability model it was demonstrated that the probability of porpoises within 125m of the pinger initially decreased when the pinger was turned on, but then increased to equal the control in 10-11 days. Echolocation rate (p < 0.001) and occurrence (p < 0.001) were significantly reduced in the vicinity of the pinger. These results indicate that porpoises habituated to the Dukane NetMark™ 1000 pinger and are not alerted to echolocate in the presence of nets by pingers.
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Will harbour porpoises (Phocoena phocoena) habituate to
Tara M. Cox
, Andrew J. Read
, Andrew Solow
And Nick Tregenza
Contact e-mail:
Large bycatches of harbour porpoises (Phocoena phocoena) occur in gillnet fisheries throughout the Northern Hemisphere. Several
mitigation measures, including acoustic deterrent devices or ‘pingers’, have been used in efforts to reduce this bycatch. The potential exists
for harbour porpoises to habituate to pingers, thus reducing their effectiveness over time. A field experiment was conducted to test the
hypothesis that porpoises habituate to the sound produced by pingers. Porpoise echolocation and movements were monitored around a
mooring equipped with a pinger (Dukane NetMark™ 1000) for three months in summer 1998 in the Bay of Fundy. Using a mean-shift
model it was estimated that porpoises were initially displaced 208m from the pinger (p=0.019), but this displacement diminished by 50%
within four days (p=0.019). Using a probability model it was demonstrated that the probability of porpoises within 125m of the pinger
initially decreased when the pinger was turned on, but then increased to equal the control in 10-11 days. Echolocation rate (p<0.001) and
occurrence (p< 0.001) were significantly reduced in the vicinity of the pinger. These results indicate that porpoises habituated to the Dukane
NetMark™ 1000 pinger and are not alerted to echolocate in the presence of nets by pingers.
Large numbers of dolphins and porpoises die in gillnets
worldwide, posing serious threats to several populations and
species (Jefferson and Curry, 1994; Perrin et al., 1994).
Acoustic alarms or ‘pingers’ are currently used in several
fisheries to reduce these bycatches (Kraus et al., 1997;
Cameron, 1998; Trippel et al., 1999; Gearin et al., 2000). As
the use of pingers spreads, concerns have been raised about
their long-term effectiveness (Dawson et al., 1998). This
issue of acoustic alarms has recently been reviewed by the
Scientific Committee of the International Whaling
Commission (IWC, 2000).
One of the most intensive efforts to reduce small cetacean
bycatch has occurred in the Gulf of Maine. Between 1992
and 1996, an average of 2,100 harbour porpoises (Phocoena
phocoena) died annually in Gulf of Maine sink gillnets -
approximately 4% of the estimated population of 54,300, a
rate that greatly exceeded allowable removal levels set under
USA legislation (Waring et al., 1999). Kraus et al. (1997)
demonstrated that pingers caused a significant reduction in
the bycatch rate of harbour porpoises in the Gulf of Maine.
Fishermen have taken an active role in the development and
testing of pingers and are supportive of their widespread use
in this fishery. Consequently, the use of pingers was
recommended as an integral component of the management
plan designed to reduce incidental mortality to sustainable
levels (Federal Register, 1998).
In addition to recommending the use of pingers in the Gulf
of Maine, the management plan recommended that research
be conducted on several aspects of their use, including the
potential for habituation. Habituation is defined as ‘the
relatively permanent waning of a response as a result of
repeated stimulation which is not followed by any kind of
reinforcement’ (Thorpe, 1966). Participants at a workshop
sponsored by the US National Marine Fisheries Service and
the Marine Mammal Commission also noted the possibility
that the effectiveness of pingers could decline due to
habituation (Reeves et al., 1996). As more and more pingers
are used in the Gulf of Maine, the avoidance response of
harbour porpoises to these pingers could wane, reducing the
efficacy of this management tool.
The purpose of this study was to evaluate the potential for
porpoises to habituate to pingers. This experiment,
conducted in the summer of 1998, forms part of a larger
research programme designed to address the question of
habituation. Another important aspect of this overall
programme is to monitor the observed bycatch rate of
porpoises over time in areas where pingers are used, to
determine whether or not habituation is occurring. In the
field experiment described here, a technique similar to that
employed by Koschinski and Culik (1997) is used, in which
shore-based observers used a theodolite, or surveyor’s
transit, to track the movements of porpoises in the vicinity of
active pingers. In a study of six days duration, Koschinski
and Culik noted that porpoises avoided an experimental net
equipped with pingers. Similar findings have been reported
by Kastelein et al. (1997) for porpoises in a captive setting.
In this study, patterns of harbour porpoises were monitored
in relation to pingers over longer periods to assess the
potential for habituation.
Study area and experimental design
Porpoises were observed from a cliff on Grand Manan
Island, New Brunswick, Canada between 26 June 1998 and
14 September 1998. This area has a high density of harbour
porpoises during the summer months (Waring et al., 1999).
A single Dukane NetMark™ 1000 pinger was attached 10m
below the surface to a mooring at 44°47.7’N, 66°48.2’W
(Fig. 1). The mooring was approximately 1,000m offshore
and was set in 75m of water. The Dukane NetMark™ pinger
emits a regular interval pulsed, broad-band signal with a
fundamental frequency of 10kHz and a minimum sound
pressure level of 132dB re 1mPa at 1m, which meets the
Duke University Marine Laboratory, Beaufort, NC 28516 USA.
Marine Policy Center, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 USA.
Cornwall Wildlife Trust, Penzance, Cornwall TR20 8JE, UK.
J. CETACEAN RES. MANAGE. 3(1):81–86, 2001 81
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current regulatory specification for a pinger in the Gulf of
Maine (Federal Register, 1998). During an initial two-week
training period, porpoises were tracked by the study team to
improve proficiency in the use of the theodolite (see below).
Porpoises were then tracked for two weeks around the
mooring while the pinger was attached but not turned on -
Control 1 (Table 1). On 11 July, the pinger was turned on and
porpoises were tracked for four weeks - Experimental Trial
1. On 7 August, the pinger was turned off, and tracking
began again on 19 August - Control 2. At this time a porpoise
echolocation detector, POD, was also attached (see below).
On 2 September the pinger was turned back on, and tracking
continued for four weeks - Experimental Trial 2.
The sound pressure level and frequency of the Dukane
pinger decrease with decay in battery voltage (Trippel et al.,
1999), so the pinger batteries were changed once a week and
the voltage of each battery was tested after it was
Two researchers tracked porpoises using a Geodolite 404
total station and a Husky FS/GS data collector from a 100m
cliff approximately 1,000m from the mooring. The
observational area encompassed a 500m radius around the
mooring. One researcher, the surveyor, used Fujinon 7 3 50
binoculars to scan the observational area for porpoises. The
surveyor looked in concentric circles around the mooring,
extending out to 500m. This individual reported sightings of
porpoises to the tracker, the researcher stationed at the
theodolite. The tracker used the theodolite to track
surfacings of the lead porpoise in a group until: (1) the
animals left the study area; or (2) the tracker lost sight of the
porpoises or could not confirm that it was the same group.
The tracker then began tracking the next group of porpoises
identified by the surveyor. During the training period, the
researchers tested their ability to estimate 500m from the
mooring in all directions. The theodolite was used to
measure the distances and ground-truth the estimates. After
two weeks of training, both researchers were able to estimate
500m to within 10m in all directions.
On 20 August 1998 a POD was attached to the mooring. The
POD continuously logged the number of echolocation clicks
in 10s intervals. The POD was programmed to record several
Fig. 1. Study area at Grand Manan Island, New Brunswick, Canada. The star represents the position of the
pinger mooring. Track of satellite tagged animal from 6 August 1998 to 16 September 1998 (Westgate
and Read, unpublished data). Individual points represent best position per day.
channels of echolocation clicks of varying duration and
frequency. The frequencies were fixed at 50kHz, 93kHz and
132kHz. Porpoises produce distinctive narrow band sonar
clicks from 110-150kHz (Mohl and Andersen, 1973;
Kamminga and Wiersma, 1981) and so only clicks at
132kHz were used in the analysis. Single click durations for
harbour porpoises are typically 100ms (Mohl and Andersen,
1973), so the POD was programmed to capture any click that
lasted up to 400ms in duration.
Response variables
From the results of previous studies, a change in porpoise
behaviour was expected when the pinger was first activated.
Then, if habituation occurred, a gradual waning of this
response was expected to occur over the experimental
period. Three variables that have direct relevance to
entanglement were examined: the point of closest approach
to the pinger, echolocation rate and echolocation
occurrence. The point of closest approach was defined as the
minimum distance between the pinger and a surfacing
porpoise. Echolocation rate was the number of clicks
recorded per unit time and echolocation occurrence was the
proportion of 10 second intervals in which clicks were
Sound field
The sound field radiated by the pinger was measured on 26
September 1998. The day was overcast and the Beaufort Sea
State was 2, diminishing to 1. Researchers drifted past the
mooring in a small boat while the position of the boat was
recorded from shore using the theodolite. The observers in
the boat monitored the sound produced by the pinger with a
Bruel and Kjaer 8100 calibrated hydrophone and a 2635
charged coupled pre-amplifier, which included a reference
signal (160Hz, 174dB re1mPa@1m) generator. The
weighted hydrophone was deployed 10m below the drifting
boat. The calibration signal and hydrophone signal were
recorded on a Sony TCD-D8 DAT recorder. Using
Syntrillium Software Corporations Cool Edit Pro version
1.1, the recordings were uploaded using 16-bit, single-track
settings. A power spectrum (FFT 1,024 points;
Blackman-Harris window) was then created to estimate the
sound pressure level of the pinger in relation to the reference
signal. By comparing the relative decibel level of the pinger
to the known decibel level of the reference signal, the
absolute decibel level of the pinger could be calculated.
Two models were used to examine the data. First, a
mean-shift model was used to test the hypothesis that
porpoises were initially displaced from the pinger and then
gradually moved closer to the pinger:
) = b
+ b
) is the expected distance of closest approach for group
j (j = 1, 2, 3, ., n)
, b
, and b
are unknown parameters:
is the control mean
is the mean shift due to the pinger
is the rate at which the pinger effect decays to 0
is the day on which group j was observed
is the day the pinger was turned on
) = 1 if t
> t
, otherwise I
) = 0.
Under this model, mean distance (b
) is constant prior to
activation. Following activation, there is an immediate
increase (b
) in the mean distance. This increase declines
with time at rate b
. The time after t
at which the mean shift
has been reduced by 50% can then be defined as:
= log 0.5 / b
To test whether there was an initial response when the pinger
was turned on, the null hypothesis H
: b
= 0 was tested
against the one-sided alternative hypothesis H
: b
> 0.
Using a randomisation test (Manly, 1991) samples were
generated under H
by randomising the assignment of the
observed values of Y
to observation dates and fitting the null
model by least squares. The significance level was estimated
by the proportion of randomised datasets for which the
residual sum of squares was less than that from fitting the
model to the non-randomised data.
To test whether there was a significant waning of response
over time, the null hypothesis H
: b
= 0 was tested against
the one-sided alternative H
: b
> 0. In this case, only those
values of Y
for which t
were permuted.
Porpoises can probably not detect the pinger out to 500m
(Kraus et al., 1997) and so a second model was used to test
the probability that the proportion of sightings within 125m
changed over time in response to the pinger. The distance of
125m was chosen based on sound field analysis (see below)
and Laake et al.s (1998) published displacement distance.
The general model is:
= 1) = p
0 t
< t
< q
where t
is the known day of activation of the pinger and q
corresponds to the beginning of the habituation period. The
binary random variable was chosen as X
= 1 if the closest
approach of group j is within 125m of the pinger and 0
otherwise, and t
was chosen as the day on which this group
was observed. Under this model the probability of a sighting
within 125m prior to activation (p
) is constant. Following
activation this probability falls to p
. However, beginning on
day q, this probability rises to p
Each of the following null hypotheses was tested against
the general model:
Hp p p
Hp p
Under H
, there is no effect of the pinger on proportion of
porpoises within 125m. Under H
there is an effect, but no
habituation. Under H
, there is full habituation. In each case
the likelihood ratio statistic was used. In testing H
and H
against the general model, randomisation tests were used.
The former case involved randomising the full set of
observed distances; the latter case involved randomising
only the post-activation distances.
A univariate factorial analysis of variance was used to
examine variation in echolocation rate as a function of the
state of the pinger (on or off) and time of day. Day was
defined as occurring between 07:00 and 18:59 and night
occurred between 19:00 and 06:59 (Westgate et al., 1995). A
Chi-squared test was also used to compare the proportion of
10s intervals in which echolocation clicks occurred when the
pinger was off and on. Means are presented with their
associated standard deviations.
The closest observed approach of the porpoises to the active
pinger decreased over time (Fig. 2). Poor weather forced
truncation of the second trial. Thus the sample size was
J. CETACEAN RES. MANAGE. 3(1):8186, 2001 83
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small, so both experiments were pooled to increase the
power and test the mean-fit model. Results of the mean-shift
model for both experimental trials and the pooled trials are
presented in Table 2.
For the probability model all three null hypotheses were
tested for Trial 1. Trial 2 was truncated, so only an effect of
the pinger was tested. In Trial 1, the null hypotheses of no
effect (p=0.02) and no habituation (p=0.0) were rejected;
however, the null hypothesis of full habituation (p=0.39)
was not rejected. The maximum-likelihood estimates of the
parameters under full habituation were:
p p p days
02 1
0 30 0 00 10 11== = =-
It is not possible to distinguish between habituation times of
10 or 11 days because no observations were made on Day 11
following activation. For Trial 2, there was no significant
difference between the p
(0.19) and p
(0.08) (p=0.12).
A time of 30 minutes was chosen for the analysis of
echolocation rate because only one group of porpoises
remained in the area for more than this period (31 minutes).
Therefore, independence among measurements of the
number of echolocation clicks per half hour was assumed.
Echolocation detection rate for the control (516±2,062;
n=288) was significantly greater than when the pinger was
active (82±366; n=496) (p<0.001). In addition,
echolocation detection rate was higher at night (377±1,699;
n=432) than in the day (75±409; n=352) (p<0.001) for
both control and active periods. The proportion of 10 second
intervals in which clicks were detected decreased after the
pinger had been activated (control=0.174;
experimental=0.041) (c
=9,241; p < 0.001).
Received sound pressure levels of the 10kHz signal
became indistinguishable from background noise at
approximately 125m from the pinger (Fig. 3). Battery
voltages averaged 5.85V ± 0.06V when removed from the
The analysis suggests that porpoises habituated to the
presence of the pinger. Both models indicated an initial
response and then a waning of that response. When the two
trials were pooled in the mean-shift model, porpoises were
initially displaced from the pinger, but this displacement
waned over time. Despite a small sample size and truncation
of the second trial, similar patterns were observed in each of
the two individual trials in the mean-shift model. In addition,
the probability that porpoises approached within 125m of the
pinger initially decreased, then increased after 10-11 days.
Thus, porpoises habituated to the pinger and approached it
more closely over time.
Demonstration of habituation typically relies on repeated
observations of known individuals (Richardson et al., 1995).
Fig. 2. Closest observed approach for Trials 1 and 2 pooled. (-) = Control, Trial 1; (/) = Experimental, Trial 1;
(8) = Control, Trial 2; () = Experimental, Trial 2.
0 50 100 150 200 250 300
Distance (m)
It was not possible to identify individual porpoises as their
movements were tracked with the theodolite. However,
previous studies of the movements of porpoises in the Grand
Manan area using satellite and VHF telemetry have shown
that individual animals are present in particular areas for
weeks or months (Read and Westgate, 1997). For example,
a porpoise tagged with a satellite-linked radio transmitter
was tracked around the mooring on 1 September 1998. This
porpoise had been in the area for several weeks (Fig. 1).
Thus, individual porpoises likely experienced multiple
exposures to the pinger over the course of the experiment.
The estimate using the mean-shift model of an initial
displacement of 208m is larger than the 125m displacement
used for the probability model. In addition, the time to
response decay in the mean-shift model is considerably
faster than the estimate of 10-11 days using the probability
model. However, the precision of estimates of initial
displacement and rate of decay in the mean-shift model is
relatively low, since few observations were made
immediately after the pinger had been activated. The results
show a relatively large initial displacement, followed by a
relatively rapid habituation. However, no observations were
made immediately following activation of the pinger, so the
possibility of a smaller initial displacement and a longer
period of habituation can not be ruled out. Nevertheless, this
imprecision does not affect the conclusions that porpoises
were initially displaced by the pinger and then approached it
more closely over time.
The experimental protocol involved only a single pinger
on a mooring, so it is not possible to say with certainty that
porpoises will habituate to pingers attached to a gillnet. In
fact, even if habituation occurs, it may not lead to an increase
in bycatch rate if there is enough residual effect to keep
porpoises away from nets. Another plausible scenario is one
in which as porpoises habituate and approach the pinger
more closely, the sound may stimulate them to investigate
their surroundings more thoroughly and thus avoid the net.
This scenario assumes that the porpoise will perceive the net
as a barrier or danger. Ultimately, a monitoring programme
is necessary to ensure bycatches do not increase as porpoises
habituate to pingers used in a commercial setting (IWC,
The decrease in battery voltage would not have resulted in
a significant decay in frequency or amplitude of the pinger
(Trippel et al., 1999). However, it is unlikely that fishermen
will replace batteries every week. Thus, battery decay and
resultant changes in pinger function could lead to a decay in
their effectiveness in a commercial fishery. Pingers are
currently being developed that regulate the voltage supply so
that frequency and sound pressure do not decay with falling
battery voltage (A.D. Goodson, pers. comm.).
The experimental protocol also only involved a single
type of pinger - the Dukane NetMark 1000. Other types of
pingers with different sound characteristics, including
frequency sweeps as opposed to tonal pulses, varied
inter-pulse intervals and randomised frequency over time,
are currently being developed (A.D. Goodson, pers. comm.).
As these pingers become commercially available, they
should be thoroughly tested to determine if they will reduce
the likelihood of habituation.
Elucidating the mechanism by which pingers work will
further aid in determining if porpoises will habituate to
pingers on gillnets (see below). For example, if the sound of
pingers is aversive to porpoises, they are likely to habituate
to it. However, if pingers alert porpoises to the presence of a
barrier which they perceive as dangerous, they may be less
likely to habituate.
Kraus et al. (1997) hypothesised that pingers might
stimulate porpoises to echolocate and thus detect a gillnet.
This hypothesis was tested here by examining echolocation
rates of porpoises in relation to the moored pinger. The
reduction in echolocation rate (number of clicks per unit
time) when the pinger was activated demonstrated that
porpoises were either echolocating less frequently in the
vicinity of the pinger, using shorter click trains, or directing
their sonar away from the pinger. If porpoises emitted a
Fig. 3. Sound power spectrum level (dB re 1mPa) versus distance from the pinger. (5)= Drift 1; (U) = Drift 2;
(D)= Drift 3. At approximately 125m, the 10kHz peak in the power spectrum became indistinguishable from
background noise.
J. CETACEAN RES. MANAGE. 3(1):8186, 2001 85
similar number of shorter trains, the proportion of 10s
intervals containing clicks would be expected to be similar in
control and experimental treatments. However, the
proportion of 10s intervals in which echolocation events
occurred was significantly reduced when the pinger was
activated, suggesting that porpoises echolocate less
frequently in the vicinity of an active pinger.
It is possible, and perhaps likely, that many porpoises
were displaced from the pinger and the POD did not detect
their echolocation signals. Preliminary studies estimate the
range of the POD to be 50-100m (T. Cox, unpublished data).
This distance is considerably greater than the distance
(2-9m) at which porpoises can detect nets with floatlines
using echolocation (Hatakeyama and Soeda, 1990). None of
these explanations supports the hypothesis of Kraus et al.
(1997) that the Dukane NetMark 1000 pinger stimulates
porpoises to echolocate, as the echolocation frequency of
porpoises around the pinger did not increase when the device
was activated.
Even during the control period, echolocation clicks were
recorded only 17% of the time. Porpoises were tracked
around the mooring at this time, and three times porpoises
were oriented towards the mooring within 50m of the pinger,
but no echolocation clicks were recorded. Thus, it is likely
that porpoises are not echolocating constantly. This finding
has relevance for the development of other acoustic means of
reducing bycatch, particularly those which rely on a passive
Because Trial 2 was truncated due to poor weather
conditions, changes in echolocation response to the pinger
over time were not monitored. Future studies should monitor
echolocation rate and frequency as additional response
variables that could wane over time. Investigating these
responses over time would further elucidate the potential for
porpoises to habituate to the presence of a pinger.
The results suggest that the effects of habituation need to be
considered when pingers are used to reduce the bycatch of
small cetaceans. Long-term monitoring of bycatch using
observers is necessary to ensure the effectiveness of pingers
in gillnet fisheries (IWC, 2000). This study was not designed
to test hypotheses of the mechanism by which pingers reduce
harbour porpoise bycatch, but was able to reject the
hypothesis that pingers stimulate harbour porpoises to
echolocate and thus detect a gillnet. Monitoring harbour
porpoise echolocation around gillnets equipped with pingers
could further elucidate the mechanism by which pingers
reduce bycatch.
This research was conducted at the Grand Manan Whale and
Seabird Research Station. Special thanks go to Jeremy
Rusin, Andrew Westgate, Dave Johnston, Heather
Koopman, Krystal Tolley, Rob Ronconi and Sarah Wong for
assistance in the field. Additional assistance was provided by
the fishermen of Grand Manan, especially Jeff Foster and
Steven Bass. Equipment and aid for mapping the sound field
were provided by Dr Jack Terhune and Dave Johnston. The
experimental design was improved by comments from Jay
Barlow and the US Marine Mammal Commission and its
Committee of Scientific Advisors. We thank Dave Johnston,
Finn Larsen and Dave Goodson for their thoughtful reviews
of this manuscript. This project was funded by the US
National Marine Fisheries Service, Northeast Fisheries
Science Center under Co-operative Agreement
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... When studying the acoustic activity of harbor porpoises exposed to a 2.5 kHz "warning" sound, Koschinski et al. (2006) showed that the echolocation activity increased in groups as well as individuals. Cox et al. (2001), on the other hand, found a decrease in echolocation activity in response to a Ducane Netmark 1000 pinger, transmitting 10 kHz multiharmonic sounds. Teilmann et al. (2006) and Kastelein et al. (2000) both demonstrated that porpoises swam away from a pinger sound source which would have decreased the logged echolocation activity at the pinger. ...
... However, in Danish waters harbor porpoises exposed to Airmar pingers, emitting a 10 kHz signal with regular 4 s interval, and Save-Wave Black Saver pingers, emitting 30-160 kHz multiharmonic up-sweeps with 4-16 s intervals, indications of habituation were seen during periodic exposure (on-off pinger cycles of 2-9 days over 47 days), whereas no sign of habituation was observed during 28 days of continuous exposure to the Aquamark 100 and Aquamark 300 pingers (Kyhn et al., 2015). Cox et al. (2001), using theodolite for tracking porpoise surfacings, demonstrated by modeling, that the probability of detecting porpoises within 125 m from a Ducane Netmark 1000 pinger initially decreased when the pinger was turned on, but then increased to levels equal to the controls in 10-11 days. The pinger used in their experiment emitted regularly spaced multiharmonic signals with a 10 kHz fundamental. ...
... However, providing evidence for true habituation requires repeated observations of known individuals (Richardson et al., 1995). In our study, as well as in Kyhn et al. (2015) and Cox et al. (2001), no information on responses to pinger sounds in individual harbor porpoises was available. Therefore, we can just confirm that our model did not show a significant effect on DPM/hr of the variable Consecutive Day during our experiment. ...
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A measure proven successful in mitigating harbor porpoise bycatch, is the use of acoustic deterrents, i.e., pingers. However, most pingers are audible to seals. This may lead to seals associating pinger sounds with easily accessible food, leading to increased depredation, damage, and bycatch. In this study we tested if an experimental pinger, emitting sounds over 30 hr ON/OFF cycles, with low frequency components potentially audible to seals only at close distances, would effectively deter harbor porpoises. The porpoise response was measured by logging echolocation clicks, using C-POD click detectors, moored at different distances from the pinger. In addition, we calculated the theoretical pinger detection range for seals. Results showed that the pinger had a significant negative effect on the porpoise click activity logged at 0 m and 100 m distance but not at 400 m from the pinger. During pinger ON periods, we found no significant increase in echolocation over consecutive days of the study, suggesting no habituation to pinger sounds. Our theoretical detection distances indicate that seals can only detect the pinger at close distances, preventing seals from using this pinger as a “dinner bell.”
... Habituation of harbour porpoise has been observed in some fisheries (e.g. Cox et al., 2001;Carlström et al., 2009;Kyhn et al., 2015) but not in others (e.g. Carretta and Barlow, 2011;Sørensen and Kindt-Larsen, 2016;Northridge et al., 2019). ...
... Cetacean -Porpoise Detector (C-POD), Chelonia Limited). Harbour porpoise have been found to echolocate less frequently in the vicinity of active ADDs (Cox et al., 2001;Omeyer et al., 2020), and background noise may also mask the noise of ADDs in some areas (Hardy et al., 2012;Omeyer et al., 2020). ...
Technical Report
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Bycatch is a major conservation and welfare issue for cetaceans in European waters. Harbour porpoises and common dolphins are frequently reported to be bycaught in static nets (gillnets and entangling nets) and trawls. Despite European legislation to monitor and mitigate cetacean bycatch in fisheries where it has a negative impact on the conservation status of a species, bycatch still occurs at high rates in several fisheries in the ASCOBANS Agreement Area. The lack of compliance by some countries has resulted in legal challenges from the European Commission for implementation of the required measures. There are two main parts covered in this report. The first part reviews different mitigation measures (acoustic deterrent devices, porpoise alerting devices, reflective nets, acrylic echo enhancers, lights and various technical modifications and changes to fishing practices) that have been trialed in the ASCOBANS region. The cost of implementation and pros and cons of each method are discussed in detail in the relevant sections. The second part of the report reviews alternative fishing methods to replace static nets (i.e. gillnets and entangling nets). The cost of implementation, and pros and cons of the different gears, are discussed in depth in the relevant sections.
... Use of pingers have caused exclusion of important habitats for some species like the harbour porpoises, due to the pinger sounds 70 . In some cases, pingers have lost their efficacy in deterring animals due to habituation by some species like the finless porpoises (after an 8-month period 63 ) or the harbour porpoises (after a 10-day period 71 ). The response to pingers seems to depend on many factors, particularly the dolphin species on target 72 . ...
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Ganges River dolphins echolocate, but this mechanism is inadequate for poor sonar-echoing objects such as the monofilament gillnets, causing considerable net entanglement related mortalities. Net entanglement related deaths are one of the major causes of cetacean population decline around the world. Experiments were carried out to understand the use of pingers—an acoustic deterrent, in aiding the deterrence of dolphins from fishing nets. Based on the dolphin clicks recorded, in an experimental setup spanning 36 days, a 90% deterrence was found; 22.87 ± 0.71 SE dolphin detection positive minutes per hour near non-pingered nets versus 2.20 ± 0.33 SE per hour near pingered net. Within 30 m radii of nets, visual encounters of non-calf reduced by 52% and calf by 9%, in the presence of pingers. No evidence of habituation to pingers, habitat avoidance in dolphins after pinger removal or a change in fish catch in nets because of pingers was found during the study. While the effectiveness of pingers on calves and fish catch needs further experimentation, the use of pingers to minimize net entanglement mortalities in the Ganges River dolphins seems to be the most promising solution currently available. These results have critical implications for the conservation of other species of river dolphins around the world.
... Фиг.75. Брой наблюдения и среден брой индивиди на далян Синеморец.Резултатите показват, че при далян Синеморец са регистрирани повече наблюдения отколкото нападения (Фиг. ...
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The conflict between fisheries and cetaceans exists in many areas around the world, and the Bulgarian territorial waters of the Black Sea are no exception. In Bulgaria, almost missing studies on the conflict’s nature and extent, and the government and local authorities do not have appropriate policies for conflict management. Studies of the different fishing gears in the Bulgarian Black Sea waters and the interactions that cetaceans have with them are presented in current thesis. Various methods have been used in the dissertation aiming to identify the different sides of the interaction between Bulgarian fisheries and cetaceans.
... On way of mitigating bycatch is the use of active acoustic deterrent devicesso-called pingerswhich is mandatory in some fisheries (Council of the European Union, 2004). Despite effectively reducing bycatch of harbor porpoises (Kraus et al., 1997;Larsen and Eigaard, 2014;Palka et al., 2008), pingers have a series of drawbacks, including habituation depending on the pinger specifiations (Cox et al., 2001;Kindt-Larsen et al., 2018), catch damage due to depredation owed to the "dinner bell" effect for other marine mammals (Gilman et al., 2019;Carretta and Barlow, 2011), and potentially higher bycatch rates when a number of pingers in a series of pingers attached to gillnets fail (Carretta and Barlow, 2011). Furthermore, pingers require regular maintenance such as change of battery and verification of functionality to fulfill their task. ...
Incidental capture in gillnets is the most pressing threat for small cetaceans worldwide. One reason why small, echolocating cetaceans entangle in gillnets may be their inability to acoustically detect gillnets and classify them as obstacles. To increase the overall acoustic reflectivity as well as alter the perceived image to simulate an impenetrable barrier, small reflective objects – 8 mm wide acrylic glass spheres – were attached to standard gillnets. This study investigates the acoustic reflectivity of standard gillnets and modified gillnets with different numbers of spheres/m², at several angles of ensonification across a large frequency range. The acoustic reflectivity of standard gillnets is very low and decreases with angle of ensonification. Gillnets equipped with the spheres have substantially higher acoustic backscattering strength, and exhibit a positive relation between backscattering strength and inclination, i.e. gillnets ensonified from an angle have an even larger echo than when ensonified perpendicularly. Gillnets with sphere-sphere distance of 20 cm perform best, while the acoustic backscatter of gillnets with 40 cm and 60 cm sphere-distances is similar. The acoustic image (echogram) of the gillnet with spheres demonstrates a distinct highly visible acoustic pattern, potentially rendering the spheres an effective way to reduce bycatch of small cetaceans.
... Pingers may be a method of reducing entanglement on moorings and other lines though this technique needs additional research (Benjamins et al., 2014). Pingers have been used to successfully and significantly reduce small cetacean bycatch in some fisheries (Carretta et al., 2008;Carretta and Barlow, 2011), however, habituation to pingers may occur (particularly with pinnipeds (Cox et al., 2001)) and attention must be paid to device durability and maintenance over the long term (Dawson et al., 2013). It is important to consider that the use of acoustic deterrent devices, may result in increased noise pollution and other negative impacts, such as attracting some species to turbine areas (Carretta and Barlow, 2011;Findlay et al., 2018). ...
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Offshore wind energy is expanding globally and new floating wind turbine technology now allows wind energy developments in areas previously too deep for fixed-platform turbines. Floating offshore wind has the potential to greatly expand our renewable energy portfolio, but with rapid expansion planned globally, concerns exist regarding impacts to marine species and habitats. Floating turbines currently exist in three countries but large-scale and rapid expansion is planned in over a dozen. This technology comes with unique potential ecological impacts. Here, we outline the various floating wind turbine configurations, and consider the potential impacts on marine mammals, seabirds, fishes and benthic ecosystems. We focus on the unique risks floating turbines may pose with respect to: primary and secondary entanglement of marine life in debris ensnared on mooring lines used to stabilize floating turbines or dynamic inter-array cables; behavioral modification and displacement, such as seabird attraction to perching opportunities; turbine and vessel collision; and benthic habitat degradation from turbine infrastructure, for example from scour from anchors and inter-array cables. We highlight mitigation techniques that can be applied by managers or mandated through policy, such as entanglement deterrents or the use of cable and mooring line monitoring technologies to monitor for and reduce entanglement potential, or smart siting to reduce impacts to critical habitats. We recommend turbine configurations that are likely to have the lower ecological impacts, particularly taut or semi-taut mooring configurations, and we recommend studies and technologies still needed that will allow for floating turbines to be applied with limited ecological impacts, for example entanglement monitoring and deterrent technologies. Our review underscores additional research and mitigation techniques are required for floating technology, beyond those needed for pile-driven offshore or inshore turbines, and that understanding and mitigating the unique impacts from this technology is critical to sustainability of marine ecosystems.
... Unlike many anthropogenic noise sources in the marine environment, tidal turbine noise is likely to be temporally and spatially persistent; it is therefore possible that individuals may habituate to the turbines in the long term. Harbour porpoise responses to other anthropogenic noise sources have been shown to diminish over small temporal scales (Cox et al., 2001;Graham et al., 2019). It was not possible to identify whether habituation may have occurred to the turbines in this study because the identity of individual porpoises cannot be determined. ...
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• Uptake of tidal turbine technology to generate renewable energy has been partly limited by poor understanding of ecological impacts, including the potential for collisions between cetaceans and rotating turbine blades. To address this concern, it is necessary to identify whether cetaceans behaviourally respond to operating turbines. • A turbine in Scotland was instrumented with hydrophones to detect cetacean vocalizations. A generalized additive model was used to investigate temporal variability in harbour porpoise presence close to the turbine. As there were incidentally periods when the turbine was not operating, it was possible to determine the effect of blade rotation, whilst accounting for the potentially confounding effect of tidal flow. • Harbour porpoise presence varied intra-annually, diurnally and with tidal state. Peak presence occurred during winter (September–February), at night and at high flow speeds on the flood tide. • Porpoises exhibited significant avoidance of the tidal turbine when it was operating; avoidance increased with flow speed, whereby mean porpoise presence was reduced by up to 78% (95% CIs, 51%, 91%) on the flood tide and up to 64% (95% CI, 3%, 91%) on the ebb tide. • The temporal variability in encounter rate in the present study highlights that collision risk assessments assuming static densities probably fail to capture the temporal variability of collision risk. Future studies should conduct long-term baseline monitoring to derive encounter rates at larger spatio-temporal scales and as a reference from which to measure change in habitat use. It is also critical that the generality of the avoidance rates presented here is assessed for other sites, turbine types, array sizes and cetacean species. As the tidal industry expands, it will be important to reconcile the benefits of avoidance responses from a collision risk perspective with potential chronic effects of displacement from, or barriers between, important habitats.
... Likewise, gear modifications are fisheries-specific, being a more adequate measure to implement when a single fishery is responsible for excessive bycatches/fishing mortalities (Senko et al., 2014). According to Uhlmann and Broadhurst (2015), across all taxa encountered by gillnets and traps, this category accounts for the greatest research effort and mainly with pingers for echolocating species; although these have variable effectiveness, encompassing habituation among some species (Cox et al., 2001). ...
Small-scale fisheries (SSF) are often considered sustainable; but comprise 95% of global fishers and cumulatively evoke substantial ecosystem impacts that include collateral mortalities. Marine mammals and sea turtles are particularly vulnerable to SSF and have been the focus of conservation strategies. However, many strategies have fallen short of objectives. This study aimed to elucidate and help resolve associated issues by: compiling global efforts to mitigate marine-mammal and sea-turtle bycatches/mortalities among SSF; identifying successful outcomes and influencing factors; and then suggesting steps for mitigating remaining problems. Among 150 articles, there was exponential temporal output, with gillnets the most studied gear (67%). Approximately 71% of all publications proposed mitigation measures but of these, efficacy was assessed in fewer than 2/3. While essential for conservation, community engagement was poorly initiated—although relevant studies have increased in the last decade, which may be correlated with studies describing management approaches instead of typical bycatch assessments. Mitigation measures were assessed in a ‘strength-weaknesses-opportunities-and-threats’ analysis. Mitigation measures should benefit multiple species (‘strengths’), avoid high costs/maintenance (‘weaknesses’), be supported by community engagement and governmental aid/enforcement (‘opportunities’), and consider non-compliance (‘threats’). Collateral mortalities can be reduced among SSF, but regional adoption of technology requires impetus that is best achieved via community engagement.
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High numbers of harbor porpoises (Phocoena phocoena) end up as bycatch in gillnets every year. Acoustic alarms (pingers) have been demonstrated to be an efficient mitigation tool to prevent bycatch of this species; however, little is known about the behavioral reactions of wild porpoises to pingers. This knowledge is important for optimizing the design and use of pingers. We tracked 16 wild porpoises with a drone and recorded their behavior before and during exposure to pinger sounds. Range from the pinger to the porpoise was 158–797 m when the pinger was first activated. In four of the exposures, with pinger-to-porpoise ranges of 199–521 m, reaction to the pinger was strong avoidance behavior with increased swimming speed heading away from the pinger. Average number of surfacings decreased from 3.4 surfacings/min before pinging to 2.8 surfacings/min during pinging. Eight animals were lost from the drone’s field of view as soon as the pinger playback started, indicating that they were either diving deep or speeding away from the area very rapidly. Four animals did not respond to pinger sounds, demonstrating a diversity in the behavioral response. Neither the behavior of porpoises (i.e., foraging, socializing and traveling) before sound exposure, the animal’s initial direction in relation to the sound source, nor the porpoise-to-pinger range affected their reaction in relation to the pinger. Pingers can cause very strong aversive reactions in harbor porpoises, which explains their efficiency in reducing bycatch. The strong aversive reactions may suggest that pinger use should be limited to critical time periods and regions, or that more focus needs to be put on developing acoustic devices which cause less severe behavioral reactions. At the same time, this study shows that 25 % of animals may not react to pinger sounds, indicating a great diversity in behavioral responses.
The main threat of franciscana dolphins (Pontoporia blainvillei) is the incidental bycatch in artisanal fishing gillnets. Several studies were implemented during the past two decades along with the local fishing communities in Brazil, Uruguay, and Argentina in order to address this conservation issue. Acoustic deterrent devices, commonly known as “pingers”, were shown to be one of the most effective bycatch mitigation method. Bottom longlines were tested as alternative fishing gear and resulted in reduced bycatch but fishermen found them difficult to implement. Gillnets modified to be acoustically reflective and have greater stiffness were ineffictive for reducing bycatch. The conclusions from this body of research is important for informing effective strategies for mitigating franciscana bycatch.
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Bycatch of harbour porpoises (Phocoena phocoena) occurs in most gillnet fisheries throughout the continental shelf area in the Northern Hemisphere. A few behavioural studies have attempted to ascertain the detection of a barrier consisting of passive echo enhancing structures. Past experiments with active sound added to fishing nets often did not achieve statistically significant bycatch reduction due to small sample sizes (reflecting a low catch per unit effort of nets). Using inoffensive experimental ‘nets’, behavioural data obtained by theodolite tracking can yield larger sample sizes. Three different device types mounted on a floatline were tested for their potential rule in reducing bycatch. For this purpose behavioural responses (avoidance and closest approach) of porpoises to these devices were compared to responses to a control which consisted of a floatline only. The devices were two different passive reflectors (target strength ranging from -38dB to -24dB) and a 2.9kHz pinger with a source level of 115dB (re 1 μPa at 1 m). A total of 335 porpoise groups (distributed in almost equal proportions for all treatments) were recorded. 92.4% of porpoise groups avoided the pinger equipped floatline whereas only about half of the groups avoided the other stimuli (reflectors: 48.6% and 58.9%. floatline only: 51.8%). The difference between pingers and all the other stimuli was significant. Closest observed approach distances were 34m (SE = 3.57) for the floatline only. 33m (SE= 3.65) and 30m (SE = 3.38) for the reflectors and 133m (SE = 6.60) for the pingers, the difference between pingers and all the other stimuli being significant. Schooling was observed in 36% of the groups with more than two individuals near the pingers. Since porpoise density in the area did not decrease after permanent use of pingers for six days there is no indication for long-term displacement from the area. The porpoises may have habituated to the sound of the pingers since frequency of avoidance and minimum distance to pingers decreased towards the end of the six week study period. This trend was not significant, however. Suggestions for future research are given.
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Demersal gill nets equipped with acoustic alarms reduced harbour porpoise (Phocoena phocoena) by-catch rates by 77% over those without alarms in the Swallowtail area of the lower Bay of Fundy during field testing in August 1996 (68% reduction) and 1997 (85% reduction) (both years combined, three harbour porpoises in 249 alarmed nets versus 14 harbour porpoises in 267 nonalarmed nets). The alarms spaced 100 m apart along the net floatline produced a 0.3-s pulse at 10-12 kHz ever y4sa t al evel of 133-145 dB re 1 μPa at 1 m. In conditions of no rain and low wind (Sea State 0-2) the alarms were presumed to be clearly audible to harbour porpoises at ranges of 0.1- 0.6 km. Catch rates of Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua), and pollock (Pollachius virens) were not significantly different in alarmed and nonalarmed nets (except in one season when pollock were caught in lower numbers in alarmed nets). Harbour porpoise by-catch and herring movements may be linked. During years of low herring abundance, we also observed low harbour porpoise entanglement rates.
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Field tests were conducted on the effectiveness of acoustic alarms (pingers) in reducing the incidental catch of harbour porpoise (Phocoena phocoena) in a salmon gillnet fishery in northern Washington in July and August of 1995-1997. The alarms produced a broadband signal with peaks at 3 and 20kHz, with mean source levels between 121.7-124.7dB re 1 mu Pa at 1m. For 1995 and 1996 combined, 47 harbour porpoise were taken in control nets and only two were taken in alarmed nets. The alarms significantly reduced the bycatch of harbour porpoise for both seasons (1995: chi super(2) = 5.28, df = 1, p = 0.02; 1996: chi super(2) = 11.2, df = 1, p = 0.001). In 1997, all nets were alarmed and 12 porpoise were taken; however, the expected catch without alarms would have been 79. There were no significant differences in catch rates of chinook salmon (Oncorhynchus tshawytscha) ( chi super(2) = 0.31. df = 1, p = 0.58), or sturgeon (Acipenser sp.) ( chi super(2) = 1.44, df = 1, p = 0.23) in control or alarmed nets. There were also no significant differences in the bycatch of harbour seals (Phoca vitulina) ( chi super(2) = 0.09, df = 1, p = 0.76) or depredation of salmon by seals in nets with and without alarms ( chi super(2) = 0.07, df = 1, p = 0.79). The results of these studies indicate that acoustic alarms significantly reduce the probability of harbour porpoise entanglement in bottom-set gillnets in the fishery without reducing the catch of target fish species.
Mean dive depths and duration ranged from 14±16 to 41±32 m, and from 44±37 to 103±67 s, respectively. The maximum recorded dive depth and duration was 226 m and 321 s. This performance may not represent the maximum capacity of harbour porpoises but rather the maximum depth of the study area. Individual dives had similar rates of descent and ascent. Two porpoises with monitoring periods >2days demonstrated a diel pattern in their diving, making fewer, but deeper dives at nights. In the Bay of Fundy, porpoises made between 22 and 70% of dives to depths (range 20-130 m) where the majority of entanglements in ground fish gill nets were reported. -from Authors