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Long-term effectiveness of pingers on finless porpoises of a small population in Japan

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Long-term effectiveness of pingers on finless porpoises of a small population in Japan

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Finless porpoises Neophocaena spp. are under pressure from various anthropogenic impacts due to their coastal habitat. Net fishery bycatch is considered a major risk for the populations around Japan, and mitigation measures are required. We carried out a long-term study to assess the efficiency of acoustic pingers in reducing the encounter rates of narrow-ridged finless porpoises with fishing nets. We used a passive ultrasonic event recorder (A-tag) to obtain acoustic encounter rates of echolocating finless porpoises and compared results for the presence and absence of pinger transmissions in Omura Bay, Japan, over two 8-mo periods (2011 and 2012). Encounter rates were significantly lower during periods when pingers were in operation, but the effect of pingers decreased with time. By the eighth month of the study in each study year, the number of encounters during the ensonified period was greater than that during periods without pingers, suggesting habituation. When pingers were reactivated at the study site after 4 mo of silence, the encounters with the active pingers returned to the lower level observed at the beginning of the experiment. These results reveal that the pingers effectively induce avoidance in porpoises, but that this effectiveness only lasts for a few months, which is likely due to habituation which could be mitigated by alternating periods of several months of silence between periods of active pinger use.
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ENDANGERED SPECIES RESEARCH
Endang Species Res
Vol. 32: 35– 40, 2017
doi: 10.3354/esr00776 Published January 12
INTRODUCTION
Of the various anthropogenic impacts on popula-
tions of small coastal cetaceans, which include ha -
bitat loss and degradation, and collision with ves-
sels, bycatch in net fisheries is considered the most
serious in many habitats (Read et al. 2006). Various
measures to reduce bycatch in terms of regulations
of scale and period have been proposed, e.g. ban-
ning of the fishery, time/area fishery closure, im -
provement of fishing gear, and use of deterrent de -
vices. The effectiveness of these measures depends
on the type of fishery involved, as well as the bio-
logical characteristics of the target species. In cir-
cumstances in which a ban on a certain type of
fishing gear or closure of the fishery is not appro-
priate, acoustic deterrent devices might be an ef -
fective measure for reducing bycatch.
The effectiveness of acoustic pingers to mitigate
bycatch of several cetacean species has been docu-
mented previously (e.g. harbor porpoises Phocoena
phocoena, Kraus et al. 1997, Palka et al. 2008, Larsen
& Eigaard 2014; common dolphins Delphinus delphis
and beaked whales, Barlow & Cameron 2003, Car-
retta et al. 2008, Carretta & Barlow 2011; francis-
canas Pontoporia blainvillei, Bordino et al. 2002),
however, this effectiveness is not evident for bottle-
nose dolphins Tursiops truncatus (Cox et al. 2004,
McPherson et al. 2004). Although no evidence of
habituation has been reported for large-scale appli-
cations of pingers in gillnet fisheries (Palka et al.
2008, Carretta & Barlow 2011), other experimental
© The authors 2017. Open Access under Creative Commons by
Attribution Licence. Use, distribution and reproduction are un -
restricted. Authors and original publication must be credited.
Publisher: Inter-Research · www.int-res.com
*Corresponding author: m-amano@nagasaki-u.ac.jp
Long-term effectiveness of pingers on a small
population of finless porpoises in Japan
Masao Amano1,*, Miku Kusumoto1, Misaki Abe1, Tomonari Akamatsu2,3
1Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Nagasaki 852-8521, Japan
2NRIFS, Fisheries Research Agency, Fukuura, Kanazawa, Yokohama, Kanagawa 236-8648, Japan
3CREST, Japan Science and Technology Agency, Gobancho, Chiyoda-ku, Tokyo 102-0075, Japan
ABSTRACT: Finless porpoises Neophocaena spp. are under pressure from various anthropogenic
impacts due to their coastal habitat. Net fishery bycatch is considered a major risk for the popula-
tions around Japan, and mitigation measures are required. We carried out a long-term study to
assess the efficiency of acoustic pingers in reducing the encounter rates of narrow-ridged finless
porpoises with fishing nets. We used a passive ultrasonic event recorder (A-tag) to obtain acoustic
encounter rates of echolocating finless porpoises and compared results for the presence and
absence of pinger transmissions in Omura Bay, Japan, over two 8-mo periods (2011 and 2012).
Encounter rates were significantly lower during periods when pingers were in operation, but the
effect of pingers decreased with time. By the eighth month of the study in each study year, the
number of encounters during the ensonified period was greater than that during periods without
pingers, suggesting habituation. When pingers were reactivated at the study site after 4 mo of
silence, the encounters with the active pingers returned to the lower level observed at the begin-
ning of the experiment. These results reveal that the pingers effectively induce avoidance in por-
poises, but that this effectiveness only lasts for a few months, which is likely due to habituation
which could be mitigated by alternating periods of several months of silence between periods of
active pinger use.
KEY WORDS: Bycatch · Pinger · Neophocaena asiaeorientalis · Small cetacean · Bioacoustics
O
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Endang Species Res 32: 35– 40, 2017
studies have suggested the occurrence of habituation
to pinger alarms (Kraus 1999, Cox et al. 2001, Carl-
ström et al. 2009), and Dawson et al. (2013) stated
that habituation might occur for inshore and resident
populations. Habituation could increase the risk of
bycatch by increasing the chances of porpoises
approaching the nets, although there is no conclusive
evidence to support this (Dawson et al. 2013).
Finless porpoises Neophocaena spp. are primarily
coastal odontocetes that are distributed in inshore
waters and several large rivers in southern and east-
ern Asia. Their usual habitats are waters shallower
than the 50 m isobath with soft-bottom substrates
(Shirakihara et al. 1994, Amano et al. 2003, Jefferson
& Hung 2004). Due to their coastal habitat, finless
porpoises are considered to be under serious threat
from anthropogenic activities in many regions (Jef-
ferson & Hung 2004, Reeves & Wang 2012, Wang &
Reeves 2012, Shirakihara & Shirakihara 2013). Por-
poises in the Yangtze River, China, in particular,
have an estimated 5% annual decline rate, with by -
catch in nets being one of the major causes of mortal-
ity (Wang 2009). In Japan, based on an interview sur-
vey, over 200 porpoises were estimated to be taken
incidentally every year in Ariake Sound; this is > 5
times more than the potential biological removal
(PBR) calculated for this pop ulation (Shirakihara &
Shirakihara 2013). Therefore, effective mitigation
measures for by catch are required for finless
porpoises.
There is a small population of 200 to
300 narrow-ridged finless porpoises N.
asiaorientalis inhabiting Omura Bay,
western Kyushu, Japan (Fig. 1) (Yoshida
et al. 1998). Finless porpoises of this pop-
ulation are well differentiated from adja-
cent populations by skull morphology
(Yoshida et al. 1995), mtDNA haplotype
frequency (Yoshida et al. 2001), and calv-
ing season (Shirakihara et al. 1993),
which suggests limited immigrations
from adjacent populations. Further, only
a single mtDNA haplotype was detected
in this population (Yoshida et al. 2001),
indicating lower genetic diversity. All
these facts suggest that this population is
vulnerable to demographic and environ-
mental stochastic factors. Bycatch of fin-
less porpoises in gillnets and set nets
does occur in Omura Bay, with the re-
ported number of bycatches being 4 to 5
animals annually for the past 5 yr. How-
ever, the actual number might be greater
than 10 individuals, which would exceed the PBR that
is estimated at approximately 4 animals (M. Amano
unpubl. data).
There are many small - scale gillnet and set net
fisheries operating along the coast of Omura Bay, and
a fishery ban or closure, either here or elsewhere in
Japan, is usually unacceptable, as fishermen and the
Japanese government are less conscious of marine
mammal conservation and reluctant to adopt strong
management measures without unequivocal evidence
of threats. Thus, we consider that use of acoustic
deterrent devices, i.e. pingers, is the most plausible
measure to reduce bycatch. To evaluate the long-
term effectiveness of acoustic pingers for mitigating
bycatch of finless porpoises, a 2-yr experiment using
a passive acoustic echolocation event recorder was
carried out in Omura Bay.
MATERIALS AND METHODS
The experiment was carried out at a small set net
that was placed off Osaki Peninsula in Omura Bay,
Japan (Fig. 1) from April 2011 to December 2012. The
study area was approximately 10−15 m deep with a
muddy bottom that gradually inclined offshore. A
passive acoustic event detector (A-tag, Marine Micro
Technology; Akamatsu et al. 2005, 2010), which de -
tects ultra-sonic pulses, was deployed 40 m offshore
36
Fig. 1. Study site in Omura Bay, Japan
Amano et al.: Effectiveness of pingers on finless porpoise
from the set net at 1.5 m depth, attached to a buoy
(Fig. 2). The position of the A-tag was determined
after consideration of the detection range (about
100 m for off-axis clicks of finless porpoise; Akamatsu
et al. 2010), the recommended maximum spacing for
the pingers used (200 m; European Commission
2004), and the distance at which fishing operation
can be achieved unobstructed. The daily encounters
of finless porpoise obtained from the A-tag data fluc-
tuated (see ‘Results’), which implies that this site re -
presents only a part of the home range of finless
porpoises.
AQUAmark100 pingers (AQUATEC Group) were
used as an acoustic deterrent. These are designed to
reduce the bycatch of harbor porpoises in net fish-
eries and have been reported to effectively decrease
harbor porpoise bycatch under experimental condi-
tions (Larsen et al. 2013). Since the acoustic charac-
teristics of finless porpoise echolocation clicks are
similar to those of harbor porpoises (Akamatsu et al.
1998), we selected this pinger for our experiment.
AQUAmark 100 pingers generate wideband fre-
quency-modulated sound between 20 and 160 kHz
with a typical source pressure level of 145 dB re
1 µPa @1 m for 200−300 ms and a random interval of
5−30 s. Two pingers were deployed on the set net
(Fig. 2); one was attached on the upper rope of the
guide net (approximately 80 m from the A-tag) and
the other was attached on the rope at the entrance of
the enclosure net (approximately 50 m from the A-
tag). These positions were selected because finless
porpoises are usually caught in set nets by becoming
entangled in the guide net or drowned in the trap net
connected to the enclosure net. Both pingers were set
at a depth of approximately 30 cm. The pingers were
ensonified for approx. 2 wk, followed by a silent
period of approx. 2 wk; this approx. 4 wk cycle was
repeated from April to December 2011, after which
we set a 4 mo silent period and then
began the 2 wk on/2 wk off cycle
again at the end of April 2012 to exam-
ine whether the habituation that may
have occurred during the first year
trial period is mitigated. We had to
remove the buoy containing the A-tag
from the water several times due to
tropical storms. After the completion
of each year’s experiments the pingers
were tested to ensure they were still
working properly.
A single encounter was defined as a
series of porpoise click trains in which
the interval between adjacent trains
was <3 min, because finless porpoises rarely suspend
emitting echolocation clicks for more than 200 s
(Akamatsu et al. 2007).
We assessed the efficacy of pingers using a gener-
alized linear model (GLM). The response variable
was the number of encounters recorded each day
with a negative binomial error structure, and the pre-
dictor variable was pinger status (on or off). We
included the interaction between pinger status and
the number of days from the beginning of the exper-
iment (hereafter, day number), because the effective-
ness of the pingers appeared to decrease with time.
We performed GLMs for the 2011 and 2012 season
data separately using the glm package in R 3.2.2
(R Development Core Team 2015).
RESULTS
The number of encounters during ensonified peri-
ods was lower than that during adjacent silent peri-
ods for the first 4 mo of the study in both years
(Fig. 3). However, the encounters in the ensonified
period increased thereafter, and after 7 mo and
37
Fig. 2. Experimental setup of the A-tag and pingers at a set net
Fig. 3. Fluctuation in the number of encounters of finless porpoises detected by
the A-tag. The simple moving average of a 5-d interval is shown. Blue line in-
dicates the period without pingers (silent period) and red line indicates that
with pingers. The breaks in the data indicate the period during which the buoy
with the A-tag was retrieved due to tropical storms
Endang Species Res 32: 35– 40, 2017
reached a similar level to, or even exceeded, that in
the silent period (Fig. 3). The overall seasonal trend
in finless porpoise encounters differed between the 2
years, with the obvious decrease in summer of 2011
not observed during 2012 (Fig. 3).
The GLM revealed a significant negative effect of
the presence of pingers on daily encounters in both
years (p < 0.05; Table 1). The interaction between
active pingers and day number was positive for both
years, which indicates that encounters during the
ensonified period increased with time elapsed. There
was a negative correlation between inactive pingers
and day number in the first year but not in the
second.
No bycatch occurred in this set net during the 2-yr
experiment.
DISCUSSION
The GLM for the 2 years clearly indicated that the
presence of pingers significantly decreased the num-
ber of encounters of finless porpoises with the set net
(Table 1), implying that pingers may be effective in
reducing bycatch of finless porpoises in the gillnet
fisheries, as is evident for harbor porpoises (Dawson
et al. 2013). The present study suggests that the
pingers designed for harbor porpoises are effective
for finless porpoises as well.
The interaction between the presence of pingers
and day number was positive in both years (Table 1),
which indicates that pinger efficacy decreased over
time. The interaction between absence of pingers
and day number was negative in the first year but not
significant in the second year (Table 1). This reflects
the difference in seasonal trend of finless porpoise
encounters between the 2 years as shown in Fig. 3.
Despite this difference, the change in the effect of
active pingers was similar in both years. After the
first 4 or 5 mo, differences in the number of encoun-
ters between the periods with active pingers and
silent periods became smaller, and encounters in the
active periods actually exceeded those during the
adjacent silent periods after 7 mo of study (Fig. 3).
This might have been caused by the habituation of
porpoises to the pinger signals. After long periodical
transmission of deterrent sounds, porpoises might
have been attracted to the pingers, or the ‘dinner bell
effect’ could have occurred (Dawson 1994, Kraus et
al. 1997, Bordino et al. 2002). The fact that encoun-
ters increased just after pingers were intiated in
October and November 2011 also supports this effect
(Fig. 3). Although there is no direct evidence of
depredation from the fishing nets, finless porpoises
are known to be opportunistic feeders that prey on
various schooling fishes that are usually caught by
net fisheries (Shirakihara et al. 2008) and are occa-
sionally caught in the gill and set nets (Shirakihara &
Shirakihara 2013, M Amano unpubl. data). This
implies that finless porpoises might be attracted to
fishing gear when it is detected in the distance.
The GLM revealed a significant effect of pingers in
both years with possible habituation occurring as
mentioned above. A decrease in encounters with
active pingers occurred again after the 4 mo of
silence, indicating that the effectiveness of pingers
resumed in the second year (Fig. 3), suggesting that
habituation to the pingers was mitigated by the sev-
eral months of silence. Habituation is one of the pos-
sible drawbacks of using pingers, as this can impair
their effectiveness (Kraus 1999, Cox et al. 2001, Carl-
ström et al. 2009). The present study is the first to
report that habituation might be mitigated by re -
fraining from using pingers for a certain period of
time, and advocates the usefulness of pingers. Since
this was based only on a single experiment for a sin-
gle species, further research is required to determine
whether this is the case for other species. The 2 wk
on/2 wk off cycle of pinger activation in the current
experiment could affect the time needed to establish
habituation as well as the time to mitigate it. The con-
tinuous ensonification of the pingers might have
established habituation quicker and hindered its mit-
igation. To determine the effective application of
pingers, further studies are required to establish
under what conditions and for what periods it is nec-
essary to develop and diminish the habituation via a
more controlled experiment.
Finless porpoises show strict habitat preferences,
i.e. waters shallower than 50 m with soft-bottom sub-
strates (Kasuya & Kureha 1979, Shirakihara et al.
38
Variable Estimate SE p-value
2011 season
Pinger on −2.467 0.394 <0.001
Pinger on × day 0.007 0.002 0.003
Pinger off × day −0.010 0.002 <0.001
2012 season
Pinger on −1.042 0.230 <0.001
Pinger on × day 0.003 0.001 0.004
Pinger off × day −0.0004 0.001 0.663
Table 1. Generalized linear model parameters for encoun-
ters of finless porpoises with active/inactive pingers. Vari-
ables include pinger status (on/off) and days since the
beginning of the experiment (day)
Amano et al.: Effectiveness of pingers on finless porpoise
1992, Amano et al. 2003, Jefferson & Hung 2004), and
their populations tend to be isolated with limited
gene flow (Chen et al. 2010, Yoshida et al. 2001,
Zheng et al. 2005, Li et al. 2011, Ju et al. 2012). These
local populations are easily fragmented and their
numbers negatively affected by various anthro-
pogenic factors. A clear decline in population size
has been detected in the Yangtze River, China, and
Seto Inland Sea, Japan, with bycatch considered a
main factor responsible for this decline (Kasuya et al.
2002, Zhao et al. 2008, Mei et al. 2012, Wang &
Reeves 2012). In the Ariake Sound, Japan, approxi-
mately 200 to 300 porpoises, corresponding to 5 to
10% of the population, were estimated to be caught
annually as bycatch in gillnet fisheries (Shirakihara &
Shirakihara 2013). Reducing the threat of bycatch is
of high priority for the conservation of finless species,
and the application of pingers is one promising
method for mitigating incidental mortality.
In Japan, small-scale gillnet fisheries are widely
operated in coastal waters by one or a few fishermen
using small boats. These operations are opportunistic
depending on the resource availability and tide, but
the occurrence of bycatch tends to show seasonal
patterns in many areas, e.g. the majority of the
bycatch is reported in spring through early summer
in Omura Bay and in fall through winter in Ariake
Sound (Shirakihara & Shirakihara 2013, M. Amano
unpubl. data). The present study suggests that an
appropriate level of sound transmission exists. Over-
exposure to sound could be worse than silence,
which might attract porpoises to the fishing gear.
Thus, limited use of pingers only during periods of
large bycatch would effectively reduce the incidence
of bycatch without developing persistent habitua-
tion. The actual implementation strategy needs to be
carefully considered, since apparent increases in
bycatch rate due to improper use or malfunctioning
pingers have been reported (Palka et al. 2008, Car-
retta & Barlow 2011).
The majority of phocoenid species are coastal spe-
cies and many populations are similarly affected by
bycatch, including harbor porpoises and vaquitas
Phocoena sinus (Rojas-Bracho et al. 2006, Reeves et
al. 2013). Results from the present study demonstrat-
ing that habituation to the pinger signal can be miti-
gated by refraining from using pingers for a certain
period suggest a possible effective way to further the
conservation of these species. However, further
study of the most efficient regime of pinger usage
for different species and populations is required to
maximize the effect of pingers in reducing bycatch
mortalities.
Acknowledgements. We thank H. Yamaguchi for his consid-
erable assistance in the experiment. Izumi Marine Service,
H. Goto, and R. Leeney helped us in the field. T. Yamamoto
gave us valuable suggestions on statistics. This study was
financially supported by the Pro Natura Foundation, Japan.
The research protocol of this study was approved by the
Animal Care and Use Committee, Nagasaki University and
Fisheries Agency, Japan, according to the Fisheries Resources
Protection Law.
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40
Editorial responsibility: Andrew Read,
Beaufort, North Carolina, USA
Submitted: April 20, 2016; Accepted: October 3, 2016
Proofs received from author(s): December 5, 2016
... The Netmark 1000 pinger used in the experiment by Cox et al. (2003) transmitted 10 kHz pings with fixed 4 s intervals, whereas the experimental Banana Pinger in our study produced several slightly varying multiharmonic, frequency modulated sounds with semirandomized 4-12 s intervals (Omeyer et al., 2020), a strategy believed to reduce possible habituation effects. On the other hand, Amano et al. (2017) observed possible habituation in finless porpoises (Neophocoena asiaorientalis) to an AQUAmark100 pinger (Aquatec Subsea Ltd., Basingstoke, UK), that also transmits different multiharmonic, frequency modulated sounds with 5-30 s semirandom intervals, after 4-5 months from the start of the experiment. ...
... However, despite the apparent habituation over time, no bycatch occurred over the entire 2 years of study (Amano et al., 2017). According to Kindt-Larsen et al. (2018), as long as the reduction of bycatch is maintained, habituation to a certain extent should be considered positive, since it would reduce a possible effect of habitat exclusion. ...
Article
The franciscana (Pontoporia blainvillei) is the most endangered dolphin in the western South Atlantic Ocean due to bycatch. Our goal was to test the efficiency of a likely "seal safe" pinger (Banana Pinger, Fishtek Marine Ltd.) to ward off fran-ciscanas, as well as investigating possible side effects of habit-uation and habitat exclusion. We deployed the pinger within a grid of click detectors (C-POD, Chelonia Ltd.) in Babitonga Bay, southern Brazil, and the narrow band high frequency sonar click trains were used as a proxy for presence of the franciscanas and response to the pinger. The presence of franciscanas next to the pinger and at 100 m away decreased by 19.4% and 15.4%, respectively, when the pinger was switched on, indicating that the franciscanas avoided the area of the pinger. This avoidance response could not be seen at 400 m away. No habituation effect was noted at any distance. There was a slight gradual decrease in detections over the course of the study at all distances, which is probably related to seasonal variation in the population's habitat use, but this requires attention in future studies. The likely "seal safe" pinger sounds effectively warded off franciscanas and thus has the potential to reduce bycatch.
... Netmark 1000 pinger used in the experiment by Cox et al. (2003) transmitted 10 kHz pings with fixed 4 s intervals, whereas the experimental Banana Pinger in our study produced several slightly varying multi-harmonics, frequency modulated sounds with semi-randomized 4-12 s intervals , a strategy believed to reduce possible habituation effects. On the other hand, Amano et al. (2017) observed possible habituation in finless porpoises (Neophocoena asiaorientalis) to an AQUAmark100 pinger (Aquatec Subsea Ltd, UK), that also transmits different multi-harmonic, frequency modulated sounds with 5-30 s semi-random intervals, after 4-5 months from the start of the experiment. However, despite the apparent habituation over time, no bycatch occurred over the entire 2 years of study (Amano et al., 2017). ...
... On the other hand, Amano et al. (2017) observed possible habituation in finless porpoises (Neophocoena asiaorientalis) to an AQUAmark100 pinger (Aquatec Subsea Ltd, UK), that also transmits different multi-harmonic, frequency modulated sounds with 5-30 s semi-random intervals, after 4-5 months from the start of the experiment. However, despite the apparent habituation over time, no bycatch occurred over the entire 2 years of study (Amano et al., 2017). According to Kindt-Larsen et al. (2018), as long as the reduction of bycatch is maintained, habituation to a certain extent should be considered positive, since it would reduce a possible effect of habitat exclusion. ...
Thesis
The franciscana dolphin (Pontoporia blainvillei) is a small cetacean critically endangered in Brazil, mainly due to the high number of incidental captures in fishing nets (bycatch). In Babitonga Bay, Santa Catarina, there is a resident population which is threatened by habitat degradation. The general objective of the study was to analyze the bioacoustics, behavior, distribution, habitat use and evaluate the effectiveness of an acoustic deterrent device ("pinger") for franciscanas, at different spatial and temporal scales, by means of a passive acoustic monitoring (PAM) device called C-POD (Chelonia Ltd., UK). The acoustic behavior of franciscana was analyzed comparatively in two habitats: estuary (Babitonga Bay: BB) and open sea (Itapirubá Beach: IB). The acoustic parameters of the click trains were analyzed and the minimum inter-click interval criterion <10ms was used as a proxy for foraging/feeding behavior. The main acoustic difference observed between habitats was related to the frequency spectrum, with a bandwidth of 17kHz in BB and 10kHz in IB. Also, the click repetition rate was almost 20% higher in the estuary. Both habitats studied presented a high feeding rate (BB = 68%; IB = 58%), higher in BB (p<0.001) and at night (p<0.001), for both habitats. To analyze the habitat use and distribution of franciscanas in Babitonga Bay, sixty C-PODs stations were implemented between June and December 2018. The generalized additive model selected to describe the relationship between the occurrence of franciscanas and several environmental variables incorporated 51% of the data variation. There is a diel pattern, where franciscanas remain in the areas of high occurrence mainly in the morning. The rest of the day, the population dispersed to other areas with different seasonal patterns. Franciscana avoid areas in periods when the presence of Guiana dolphins (Sotalia guianensis) is very intense and prefer areas with a flat bottom and sandy substrate, but during the evening and dawn they goes into areas of muddy bottom predominantly for feeding. The distribution was predominant in the innermost region of the estuary, without significant use of the bay's inlet channel. The distribution was wider in winter than in spring. The entire central region of the islands, between the north and south margins of the bay, represents an important feeding area. To test the deterrent effect of Banana pinger (Fishtek Marine Ltd, UK), as well as side effects of habituation and habitat exclusion, an exposure-controlled experiment was carried out with 5 C-PODs positioned at different distances from the pinger. The data indicate that the pinger effectively withdraw the franciscanas up to 100m, but not 400m, and therefore has the potential to reduce bycatch. No habituation effects were observed at any distance. There was a gradual decrease in the presence of franciscanas over the days, probably due seasonal variations in the population's habitat use but requires attention in future studies. C-PODs were used in an unprecedented way for the study of franciscanas and showed great potential to monitor the occurrence, behavior, distribution, and habitat use of the species. The results representing an important subsidy for management of the Babitonga Bay population and for the implementation of bycatch mitigation measures for the species in general. Available at: https://repositorio.ufsc.br/handle/123456789/227086?show=full
... Life-history traits of these marine vertebrates, especially delayed sexual maturity and low reproductive rates, make them particularly vulnerable to bycatch mortality, which can lead to relatively rapid population declines when bycatch rates exceed intrinsic population growth (Baum et al., 2003;Mei et al., 2012;Jaramillo-Legorreta et al., 2017). Several management strategies are available to reduce the frequency of interactions between fisheries and marine megafauna, including fishing gear modifications (e.g., Lewison et al., 2003;Sullivan et al., 2018), time-area closures (e.g., O'Keefe et al., 2014), and acoustic alarms or deterrents (e.g., Amano et al., 2017;Clay et al., 2019a). However, the effectiveness of each management strategy is often both species-and fishery-specific (Dawson et al., 2013;Wakefield et al., 2017), and management is most effective when multiple strategies are used simultaneously (Read, 2013;Van Beest et al., 2017). ...
... While pingers are mandatory in some fisheries around the world (e.g., Barlow and Cameron, 2003;Read, 2013;Sørensen and Kindt-Larsen, 2016), there are concerns that their effectiveness might decline over time. Indeed, some studies have found evidence of pinger habituation after only 4 days (Cox et al., 2001;Carlström et al., 2009;Bowles and Anderson, 2012;Kyhn et al., 2015;Amano et al., 2017), while others suggest no such effect after more than a decade of use in active fisheries (Carretta and Barlow, 2011;Read, 2013;Sørensen and Kindt-Larsen, 2016). In addition, pingers have been suggested to be particularly effective for harbour porpoises as they result in their displacement from the area ensonified (filled with sound) by the pinger (Dawson et al., 2013). ...
Article
Full-text available
Bycatch is a significant cause of population declines of marine megafauna globally. While numerous bycatch mitigation strategies exist, acoustic alarms, or pingers, are the most widely adopted strategy for small cetaceans. Although pingers have been shown to be an effective measure for numerous species, there are some concerns about their long-term use. Bycatch is recognized as a persistent problem in waters around Cornwall, United Kingdom, where several cetacean species are resident, with harbour porpoises (Phocoena phocoena) being the most-commonly sighted. In this study, we assessed the effects of a Banana Pinger (Fishtek Marine Limited) on harbour porpoises in Cornwall between August 2012 and March 2013. Two passive acoustic loggers (C-PODs; Chelonia Limited) were deployed 100 m apart to record cetacean activity during cycles of active and inactive pinger periods. Harbour porpoises were 37% less likely to be detected at the C-POD near the pinger when the pinger was active, while they were only 9% less likely to be detected 100 m further away. The effect of the pinger was constant over the study period at both C-PODs despite the temporal variation in harbour porpoise detections. In addition, we found no evidence of reduced pinger effect with changing environmental conditions. Furthermore, harbour porpoise detections at the C-POD near the pinger did not depend on the time elapsed since the pinger turned off, with harbour porpoises returning to the ensonified area with no delay. Together these results suggest that (1) harbour porpoises did not habituate to the pinger over an 8-month period, (2) the pinger effect is very localized, and (3) pinger use did not lead to harbour porpoise displacement over the study period, suggesting an absence of long-term behavioral effects. We suggest that the deployment of pingers on fishing nets would likely reduce net-porpoise interactions, thereby mitigating bycatch of harbour porpoises and potentially other cetacean species. As the small-scale fishery dominates in United Kingdom waters, there is an acute need for cost-effective mitigation strategies with concurrent monitoring to be implemented rapidly in order to address the problem of harbour porpoise, and more generally, cetacean bycatch.
... [16][17][18]), such as time-area regulations of a fishery, technological modifications of the fishing gear, and use of acoustic deterrent devices called pingers. Despite these efforts, harbour porpoise bycatch still occurs [19]; for example, even though pingers are temporarily effective in reducing bycatch, the widespread use of them with gillnets would likely be insufficient to eliminate porpoise bycatch [20], as their effectiveness remains a subject of dispute [21][22][23][24]. ...
Article
Full-text available
Bycatch of harbour porpoises (Phocoena phocoena) by gillnets is a recognised threat to populations. To develop effective mitigation measures, understanding the mechanics of bycatch is essential. Previous studies in experimental conditions suggested foraging activity is an important factor influencing porpoises' reaction to gillnets. We acoustically observed the behaviour of wild harbour porpoises around a bottom-gillnet set-up in a commercial fishing ground, especially foraging activity. Passive acoustic event recorders (A-tags) were fixed to the ends of the gillnet, and recorded for 1 392 hours. Although harbour porpoises frequently and repeatedly appeared around the net each day, incidental bycatch occurred only three times during the observations. The stomach contents of two individuals contained mainly Ammodytes sp., which were observable around the bottom-gillnet but not targeted by the fishery. A total of 276 foraging incidents were acoustically detected, and 78.2% of the foraging activity was in the bottom layer (deeper than 25 m). Porpoises appeared around the net with more frequency on the day of a bycatch incident than on the days without bycatch. These results suggest that the harbour porpoises appeared around the bottom-gillnet to forage on fish distributed in the fishing ground, but not captured by this bottom-gillnet. Thus, porpoises face the risk of becoming entangled when foraging near a gillnet, with the probability of bycatch simply increasing with the length of time spent near the net. Bycatch mitigation measures are discussed.
... This is completely different from conventional studies just exploring biological information using small communication devices (i.e., pingers). In addition, conventional studies fundamentally explore long-term behavior of fish for more than 1 day [30][31][32][33]. In these cases, rough positions and traces were usually tracked, but precise position time-course information was not obtained. ...
Article
Full-text available
Creation of a seabed map is a significant task for various activities including safe navigation of vessels, commercial fishing and securing sea-mined resources. Conventionally, search machines including autonomous underwater vehicles or sonar systems have been used for this purpose. Here, we propose a completely different approach to improve the seabed map by using benthic (sting and electric) rays as agents which may explore the seabed by their autonomous behavior without precise control and possibly add extra information such as biota. For the first step to realize this concept, the detail behavior of the benthic rays must be analyzed. In this study, we used a system with a large water tank (10 m × 5 m × 6 m height) to measure the movement patterns of the benthic rays. We confirmed that it was feasible to optically trace the 2D and 3D movement of a sting and an electric ray and that the speed of the rays indicated whether they were skimming slowly over the bottom surface or swimming. Then, we investigated feasibility for measuring the sea bottom features using two electric rays equipped with small pingers (acoustic transmitters) and receivers on a boat. We confirmed tracing of the movements of the rays over the sea bottom for more than 90 min at 1 s time resolution. Since we can know whether rays are skimming slowly over the bottom surface or swimming in water from the speed, this would be applicable to mapping the sea bottom depth. This is the first step to investigate the feasibility of mapping the seabed using a benthic creature.
... Inshore, resident porpoise populations may be more likely to develop habituation to pingers than more migratory species (Dawson et al. 1998(Dawson et al. , 2013. The effectiveness of pingers in deterring coastal, inshore or river finless porpoises (Neophocaena spp.) from gillnets decreased after a few months, and developing regimes which include periods with no pinger use (Amano et al. 2017), as well as randomising pinger frequency, time interval and strength, may help to maintain effectiveness. Developing 'responsive pingers' for gillnets, which only emit sounds in response to cetacean echolocations, may reduce the likelihood of pinger habituation for some species (Leeney et al. 2007;Waples et al. 2013). ...
Article
Full-text available
Fisheries bycatch is one of the biggest threats to marine mammal populations. A literature review was undertaken to provide a comprehensive assessment and synopsis of gear modifications and technical devices to reduce marine mammal bycatch in commercial trawl, purse seine, longline, gillnet and pot/trap fisheries. Successfully implemented mitigation measures include acoustic deterrent devices (pingers) which reduced the bycatch of some small cetacean species in gillnets, appropriately designed exclusion devices which reduced pinniped bycatch in some trawl fisheries, and various pot/trap guard designs that reduced marine mammal entrapment. However, substantial development and research of mitigation options is required to address the bycatch of a range of species in many fisheries. No reliably effective technical solutions to reduce small cetacean bycatch in trawl nets are available, although loud pingers have shown potential. There are currently no technical options that effectively reduce marine mammal interactions in longline fisheries, although development of catch and hook protection devices is promising. Solutions are also needed for species, particularly pinnipeds and small cetaceans, that are not deterred by pingers and continue to be caught in static gillnets. Large whale entanglements in static gear, particularly buoy lines for pots/traps, needs urgent attention although there is encouraging research on rope-less pot/trap systems and identification of rope colours that are more detectable to whale species. Future mitigation development and deployment requires rigorous scientific testing to determine if significant bycatch reduction has been achieved, as well as consideration of potentially conflicting mitigation outcomes if multiple species are impacted by a fishery.
Chapter
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.
Article
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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.
Article
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Geographic variation in the skull morphology of the finless porpoise was studied with special reference to identifying local populations in Japanese waters. Twenty-five skull characters were measured for 146 specimens. These specimens were divided into five samples on the basis of available distributional information: 1) from Sendai Bay to Tokyo Bay, 2) Ise Bay and Mikawa Bay, 3) Inland Sea and the adjacent waters, 4) Omura Bay, 5) Ariake Sound and Tachibana Bay. Morphological differences were examined by the analysis of covariance and canonical discriminant analysis. The skull morphology varied among the samples. The porpoises in Ise Bay and Mikawa Bay possessed rather narrow skulls. There was no evidence that skull morphology was more similar between geographically close areas. Such geographic variation suggests that porpoises in each area rarely intermingle. We considered that there are at least five local populations in Japanese waters. © 1995, The Japanese Society of Fisheries Science. All rights reserved.
Article
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The distribution and seasonal density of the finless porpoise were examined in the coastal waters of western Kyushu, Japan in 1987--1992 by ship sighting surveys and interview surveys with fishermen and ferry crews. Interview surveys showed that the porpoise may occur rarely in Sumo Nada and the waters of northern Nagasaki Prefecture and that it was found frequently in Ariake Sound, Tachibana Bay, and Omura Bay. In ship surveys by the line transect method, mean densities in the middle and mouth of Ariake Sound were estimated as 1.31--1.60 and 0.341 individuals/km,² respectively. The porpoise density in the middle of Ariake Sound increased from September to April and showed a minimum in August. In the mouths of Ariake Sound and Tachibana Bay, the sightings became higher in summer. The porpoise distribution was considered to shift seasonally between the two seas. Water depth and distance from the coast seem to influence porpoise occurrence. Porpoises may favor depths of less than 50 m and distances of less than 2--3 nautical miles. The season of high density in Ariake Sound coincided with the reported calving season but not with the increase in the mean school size. The mean school size was 1.70 (SE 0.05). © 1994, The Japanese Society of Fisheries Science. All rights reserved.
Article
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The long-term effectiveness of acoustic pingers in reducing marine mammal bycatch was assessed for the swordfish and thresher shark drift gillnet fishery in California. Between 1990 and 2009, data on fishing gear, environmental variables, and bycatch were recorded for over 8,000 fishing sets by at-sea fishery observers, including over 4,000 sets outfitted with acoustic pingers between 1996 and 2009. Bycatch rates of cetaceans in sets with ≥30 pingers were nearly 50% lower compared to sets without pingers (p = 1.2 × 10 -6), though this result is driven largely by common dolphin (Delphinus delphis) bycatch. Beaked whales have not been observed entangled in this fishery since 1995, the last full year of fishing without acoustic pingers. Pinger failure (≥1 nonfunctioning pingers in a net) was noted in 3.7% of observed sets. In sets where the number of failed pingers was recorded, approximately 18% of deployed pingers had failed. Cetacean bycatch rates were 10 times higher in sets where ≥1 pingers failed versus sets without pinger failure (p = 0.002), though sample sizes for sets with pinger failure were small. No evidence of habituation to pingers by cetaceans was apparent over a 14-year period of use. Bycatch rates of California sea lions in sets with ≥30 pingers were nearly double that of sets without pingers, which prompted us to examine the potential "dinner bell" effects of pingers. Depredation of swordfish catch by California sea lions was not linked to pinger use-the best predictors of depredation were total swordfish catch, month fished, area fished, and nighttime use of deck lights on vessels.
Article
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Bycatch of narrow-ridged finless porpoises Neophocaena asiaeorientalis in gillnets was estimated for the Ariake Sound/Tachibana Bay population in Japan using interview-based surveys. In 2007 and 2008, the minimum number (actual number reported by all interviewees) of bycatch was 31 to 35 individuals (ind.) yr-1. The number of interviewees was 131 to 136 in each year. The bycatch estimate was 238 (95% CI 123 to 353) to 270 (95% CI 148 to 391) ind. yr-1. The estimate exceeded the potential biological removal level of this population, 27 ind., which was calculated on the basis of a published abundance estimate. The bycatch estimate accounted for 8% of the abundance. The bycatch rate was 0.237 ind. gillnetter-1 yr-1 in 2007 and 0.257 ind. gillnetter-1 yr-1 in 2008. Additional analysis of information on bycatch in the bottom-set gillnet fisheries collected from 1987 to 1992 suggested an increase in bycatch during fall and winter seasons, the possible existence of a calving ground, and age-sex related habitat use patterns. Neonates were found in a restricted area, whereas nursing calves and possible calves were seen in a wide range of waters, implying outward movement of mother-calf pairs from a calving ground. Neither neonates nor nursing calves were captured in waters deeper than 30 m.
Article
Full-text available
Active sound emitters ('pingers') are used in several gillnet fisheries to reduce bycatch of small cetaceans, and/or to reduce depredation by dolphins. Here, we review studies conducted to determine how effective these devices may be as management tools. Significant reductions in bycatch of harbour porpoise Phocoena phocoena, franciscana Pontoporia blainvillei, common Delphinus delphis and striped dolphin Stenella coeruleoalba, and beaked whales as a group have been demonstrated. For harbour porpoise this result has been replicated in 14 controlled experiments in North America and Europe, and appears to be due to porpoises avoiding the area ensonified by pingers. Two gillnet fisheries (California-Oregon driftnet fishery for swordfish; New England groundfish fishery) with mandatory pinger use have been studied for over a decade. Bycatch rates of dolphins/porpoises have fallen by 50 to 60%, and there is no evidence of bycatch increasing over time due to habituation. In both fisheries, bycatch rates were significantly higher in nets sparsely equipped with pingers or in which pingers had failed, than in nets without any pingers at all. Studies of pinger use to reduce depredation by bottlenose dolphins Tursiops truncatus generally show small and inconsistent improvements in fish catches and somewhat reduced net damage. Dolphin bycatch in these fisheries is rare, but still occurs in nets with pingers. Taken together, these studies suggest that the most promising candidates for bycatch reduction via pinger use will be gillnet fisheries in developed countries in which the bycaught cetaceans are generally neophobic species with large home ranges. We offer a set of lessons learned from the last decade of bycatch management.
Article
From 5 March to 1 July, 1999 and 2000, we made six shipboard surveys for finless porpoises (Neophocaena phocaenoides) in the Inland Sea, which is believed to be inhabited by one local population of the species. Each survey lasted 2-24 days and covered nearly the entire extension of the sea. In principle, we followed the method of Kasuya and Kureha (1979) and attempted to revisit as many ferry tracks surveyed by them as possible, but we used a greater number of observers for some selected surveys and added some new tracks. Records of strandings and incidental mortality of the species were also analyzed. Comparison of the two sets of survey data, which were about 22 years apart, did not show establishment of new habitat in the Inland Sea, but confirmed disappearance of some habitat previously occupied by the species. All the 18 tracks surveyed by both studies showed various degrees of density decline, and the decline was statistically significant for 12 of them. The sighting rate (number of finless porpoises sighted per 100 km survey) declined in both nearshore and offshore strata. Using the 18 tracks and combining all strata, we estimated that the current density was about 4% that of the late 1970s in the middle and eastern Inland Sea, while it was about 70% in the western Inland Sea. From these results, we conclude that the finless porpoise population in the Inland Sea has dramatically declined. This decline was consistent with the trends of strandings and mortalities in fishing gear. Entanglement in fishing nets is the only documented human-caused mortality for the population. However, the decline was probably a result of compound effects of various types of environmental degradation, including destruction of coastal habitats due to construction, chemical pollution, red tide and vessel traffic.
Article
We used aerial surveys and line-transect methods to estimate the abundance of the finless porpoise (Neophocaena phocaenoides) in Omura Bay, Japan. We conducted 4 surveys once each season from August 1993 to May 1994. We surveyed 621.5 km and sighted 54 porpoise groups (87 animals). In the spring survey, we detected porpoises offshore as well as inshore, whereas porpoises were mostly inshore in all other seasons. The abundance of porpoises was estimated to be 187 animals (0.6 $\text{individuals}/\text{km}^{2}$ , CV = 20%).