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Using pingers to reduce bycatch of small-cetaceans in Peru's small-scale driftnet fishery

Abstract and Figures

There is growing awareness that small-scale fisheries may have large impacts on threatened marine fauna. Bycatch of small cetaceans by the Peruvian small-scale driftnet fleet results in the deaths of thousands of animals annually. We sought to assess the effectiveness of acoustic alarms (pingers) for reducing the incidental capture of dolphins and porpoises by this fleet. Forty-three experimental trips (156 fishing sets) and 47 control trips (195 fishing sets) out of Salaverry Port, northern Peru, were observed from April 2009 to August 2011. Twenty-two percent of control sets captured small cetaceans (67 individuals) and 16% of experimental sets had captures of small cetaceans (33 individuals). The bycatch rate of experimental sets was 0.50 individuals km−2h−1, whereasfor control sets the rate was 0.80 individuals km−2h−1. This 37% reduction in bycatch rate suggests that pingers may be effective in reducing the bycatch of small cetaceans in this fishery. Catch rates of the fishery’s target shark and ray species were unchanged. Given the vast size of this fishery and its current levels of bycatch of small cetaceans (. 10,000 individuals annually), even the modest declines in bycatch we observed could result in reductions in mortality of hundreds or thousands of small cetaceans per annum. Challenges, including increased costs, to large-scale utilization of pingers have yet to be overcome. The harpooning of dolphins for use as bait will also need to be addressed for further reductions in dolphin and porpoise bycatch and mortality to be achievable.
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Using pingers to reduce bycatch of small cetaceans
in Peru’s small-scale driftnet fishery
JEFFREY C. MANGEL,JOANNA ALFARO-SHIGUETO,MATTHEW J. WITT
DAVID J. HODGSON and B RENDAN J. GODLEY
Abstract There is growing awareness that small-scale
sheries may have large impacts on threatened marine
fauna. Bycatch of small cetaceans by the Peruvian small-
scale driftnet eet results in the deaths of thousands of
animals annually. We sought to assess the eectiveness of
acoustic alarms (pingers) for reducing the incidental
capture of dolphins and porpoises by this eet. Forty-
three experimental trips (156 shing sets) and 47 control
trips (195 shing sets) out of Salaverry Port, northern Peru,
were observed from April 2009 to August 2011. Twenty-two
percent of control sets captured small cetaceans (67
individuals) and 16% of experimental sets had captures of
small cetaceans (33 individuals). The bycatch rate of
experimental sets was 0.50 individuals km
2
h
1
, whereas
for control sets the rate was 0.80 individuals km
2
h
1
. This
37% reduction in bycatch rate suggests that pingers may be
eective in reducing the bycatch of small cetaceans in this
shery. Catch rates of the sherys target shark and ray
species were unchanged. Given the vast size of this shery
and its current levels of bycatch of small cetaceans
(.10,000 individuals annually), even the modest declines
in bycatch we observed could result in reductions in
mortality of hundreds or thousands of small cetaceans per
annum. Challenges, including increased costs, to large-scale
utilization of pingers have yet to be overcome. The
harpooning of dolphins for use as bait will also need to be
addressed for further reductions in dolphin and porpoise
bycatch and mortality to be achievable.
Keywords Bycatch, catch per unit eort, gill-net, Peru,
pinger, shark, small cetacean, small-scale shery
Introduction
Small-scale sheries are globally important as food
providers and as sources of employment in many
coastal communities, particularly in the developing world
(Berkes et al., 2001; McGoodwin, 2001; Béné, 2006;
Chuenpagdee et al., 2006). Unlike industrial sheries,
which are more centralized and often have more dened
management structures, small-scale sheries are frequently
characterized by political and economic marginalization
and are often subject to minimal management and en-
forcement mechanisms (Berkes et al., 2001; McGoodwin,
2001; Dutton & Squires, 2008; Jacquet & Pauly, 2008).
A growing list of recent studies shows that small-scale
sheries can have signicant levels of incidental catch
(bycatch) of marine fauna (e.g. Moreno et al., 2006;
Jaramillo-Legorreta et al., 2007; Peckham et al., 2007;
Mangel et al., 2010; Alfaro-Shigueto et al., 2011). Attempts to
address bycatch in these sheries (e.g. through introduction
of mitigation measures or time-area closures) are challeng-
ing (Lewison et al., 2004; Campbell & Cornwelles, 2008;
Soykan et al., 2008).
The bycatch of small cetaceans has been reported in
many sheries worldwide (Jeerson & Curry, 1994; Perrin
et al., 1994; Reeves et al., 2003; Read et al., 2006). Small-scale
sheries are likely to contribute signicantly to this bycatch
(Read et al., 2006; Read, 2008). Gill-net sheries in
particular are widely regarded as some of the largest sources
of small cetacean mortality (Jeerson & Curry, 1994;
Dawson & Slooten, 2005; Read et al., 2006; Read, 2008).
The use of acoustic alarms is seen as one of the few
potential solutions to gill-net bycatch (Read, 2008). Acoustic
alarms, or pingers, are small battery-powered devices
attached at intervals along a net that emit a repeated signal
audible to small cetaceans. Pingers are successful at reducing
the bycatch of many cetacean species (e.g. Kraus et al., 1997;
Bordino et al., 2002; Barlow & Cameron, 2003; Carretta
et al., 2008; Palka et al., 2008) and their use is now a required
bycatch mitigation measure in several commercial net
sheries in the USA and Europe (NOAA & NMFS, 1997,
1998; European Commission, 2004).
In Peru shery interactions with small cetaceans have
been reported since the 1960s (Clarke, 1962; Read et al., 1988;
Van Waerebeek & Reyes, 1990). The majority of interactions
were of small cetaceans caught by the small-scale gill-net
eet and the annual take was estimated at 10,00020,000
individuals (Read et al., 1988; Van Waerebeek & Reyes, 1990,
1994). Ministerial decrees in 1990 and 1994 (Decree Nos
569-90-PE and 321-94-PE) were followed by a national law
in 1996 banning the capture of and trade in small cetaceans
(Law No. 26585,9April 1996). Subsequent monitoring
indicated that small cetaceans were still being killed in
JEFFREY C. MANGEL*(Corresponding author), JOANNA ALFARO-SHIGUETO*,
MATTHEW J. WITT,DAVID J. HODGSON and BRENDAN J. GODLEY Centre for
Ecology and Conservation, University of Exeter, Penryn, Cornwall, TR10 9EZ,
UK. E-mail jcm210@exeter.ac.uk
*Also at: ProDelphinus, Lima, Peru
Also at: Environment and Sustainability Institute, University of Exeter, Penryn,
Cornwall, UK
Received 20 January 2012. Revision requested 2March 2012.
Accepted 9May 2012.
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, Page 1 of 12 doi:10.1017/S0030605312000658
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Perus small-scale sheries but reporting was limited
(Van Waerebeek et al., 1997,2002). Using on-board
observers on driftnet vessels from the northern Peru port
of Salaverry, Mangel et al. (2010) reported that bycatch of
small cetaceans was still common and suggested that
capture rates may remain at levels seen before the 1996
ban. This study further noted that a large percentage of
this bycatch was discarded, suggesting an opportunity to
introduce bycatch mitigation measures, such as pingers, to
the shery. The purpose of our study was to assess the eect
of pingers on bycatch of small cetaceans and on target catch
within the Peruvian small-scale driftnet shery.
Methods
The fishery
Small-scale (artisanal) vessels are dened according to
Peruvian shery regulations as those with a maximum of
32.6m
3
of storage capacity, ,15 m in length, and principally
relying on the use of manual work during shing operations
(Ley General de Pesca, 2001). During April 2009August
2011 small-scale driftnet shing trips were monitored out of
the port of Salaverry in northern Peru. Vessels in this shery
set multilament nets at the ocean surface during the late
afternoon and recover the nets the following morning after a
soak time of c. 13 hours. Nets are typically 1.52km long and
have a stretched mesh of 19.125.4cm, and remain attached
to the drifting vessel during the set. This eet operates
almost exclusively over Perus continental shelf and targets
shark and ray species (primarily smooth hammerhead
Sphyrna zygaena, blue Prionace glauca, short-n mako
Isurus oxyrinchus and thresher Alopias vulpinus sharks, and
eagle rays Myliobatis spp.), although other species are
captured incidentally, including sea turtles (Alfaro-Shigueto
et al., 2011), seabirds (Awkerman et al., 2006), swordsh
Xiphias gladius, dolphinsh Coryphaena hippurus and
manta rays Manta birostris. The blubber of small cetaceans
is regularly used as bait in this shery because of durability
and perceived eectiveness at improving the catch of blue
and mako sharks (Mangel et al., 2010). This bait is derived
from harpooned individuals or from bycatch recovered
during the trip. Detailed descriptions of this shery and its
capture species can be found in Mangel et al. (2010), Alfaro-
Shigueto et al. (2010) and Table 1.
Experimental design
For the purposes of this experiment monitored vessels
undertook normal shing operations and did not deviate
from their normal procedures or shing locations. Two
shing captains, operating from six dierent vessels, were
voluntary participants in the project. Control and experi-
mental sets occurred in all months of the study except
August 2009 and 2010, when vessels underwent annual
maintenance. Vessels either set their nets continuously
without pingers (control sets) or with pingers (experimental
sets) or alternated between control and experimental sets
throughout the course of a shing trip and also alternated
whether the initial set was control or experimental. There
was some variation in net characteristics (net length and
height) and set duration between control and experimental
sets, which was accounted for in the analysis (Table 1).
Dukane Netmark 1000 pingers were used in the study.
These pingers are no longer commercially available and
were donated to the project. They have a fundamental
frequency of 1012 kHz and emit a 300 ms tone every
4seconds with a source level range of c. 120146 dB (re: 1μPa
at 1m; Barlow & Cameron, 2003). For experimental sets,
pingers were attached to the net leadline at a depth of
c. 14 m. The urgent need to begin this research (because of
high reported bycatch rates) and logistical constraints,
meant that pingers available for the trial were limited, and
were therefore spaced at 200 m intervals. Battery voltages
were checked before each trip to ensure each pinger was
functioning properly. Pingers were also checked after each
deployment and any failed units replaced. Data from those
sets with failed pingers (six units over ve sets, i.e. 3.2%)
were not included in the analysis.
Data collection
On-board observers monitored all control and experimental
shing sets. These observers were trained to maintain and
TABLE 1 Gear characteristics and shing eort for control (no
pingers) and experimental (with pingers) shing sets observed
during the study (April 2009August 2011). Values are numbers or
mean ±SD (range).
Treatment
No pingers With pingers
No. of sets 195 156
No. of small cetaceans in
bycatch
67 33
% sets with small cetacean
bycatch
22 16
% sets using bait 24 31
Stretched mesh size (cm) 19.1, 20.3, 25.4 19.1, 20.3, 25.4
Set duration (h) 12.7 ±2.4
(3.619.2)
12.7 ±2.6
(2.316.4)
Total soak time (h) 2,477.75 1,987.65
Net length (km) 2.02 ±0.33
(1.812.96)
1.98 ±0.36
(1.642.96)
Net height (m) 14.2 ±0.8
(12.814.6)
13.9 ±0.9
(12.814.6)
Net area (km
2
) 0.027 ±0.005
(0.0230.041)
0.027 ±0.005
(0.0230.041)
Net area time (km
2
h
1
) 0.343 ±0.090
(0.1000.751)
0.347 ±0.093
(0.0530.643)
2 J. C. Mangel et al.
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deploy the pingers and to monitor relevant aspects of the
shery operation as well as the target catch and bycatch of
small cetaceans. Observers also recorded the provisioning
costs (food, fuel, ice) for each trip and the gross prots
received when the catch was landed and sold. Variables
included in on-board observer monitoring were the date,
time and location of sets as well as the primary gear
dimensions and characteristics. The use of blubber from
small cetaceans as bait was also monitored. For each shing
set all target catch and bycatch was counted and identied to
the species level whenever possible. Bottlenose dolphins
Tursiops truncatus were not dierentiated between oshore
or inshore stock. Neither common dolphins Delphinus spp.
nor pilot whales Globicephala spp. were identied to species
because of uncertainties in at-sea identication (it is likely,
however, that the majority of interactions with common
dolphins were with D. capensis; Van Waerebeek, 1994;
Mangel et al., 2010). Observers also monitored whether
entangled cetaceans were alive or dead at the time of the
haul and the nal fate of each animal (released alive,
discarded dead, used as bait, used for food).
Data analysis
Pinger eectiveness was assessed using generalized linear
mixed models (GLMM). Preliminary models included xed
eects (control sets vs experimental sets, bait use) and
random eects (trip, year, season, mesh size, vessel,
captain). A random eect weather variable was not included
because of missing values but when tested separately this
variable was determined to be non-signicant. The GLMMs
were simplied sequentially to remove non-signicant xed
and random eects. The random eect of tripdominated
variation in rates of bycatch whereas variance because of the
other variables was negligible and these were therefore
removed to arrive at the minimal adequate model. The xed
eect bait usewas also determined to be non-signicant
and was removed.
The resulting minimal adequate model for testing the
impact of pinger use on bycatch of small cetaceans used a
Poisson error distribution with xed eects (control set vs
experiment set) and the random eect (trip) as well as an
oset term for shing eort: oset(log[net area × time]).
This oset term was calculated using the on-board observer
data on each sets net area (km
2
) and soak time (h) and was
therefore expressed as km
2
h
1
. Use of the log-oset allows
the intercept parameters estimated by the GLMMs to be
interpreted as catch per unit eort. Small cetacean bycatch
data were not overdispersed and model checks conrmed
that the Poisson error structure was valid. Seasons were
dened as quarter 1(JanuaryMarch), quarter 2(April
June), quarter 3(JulySeptember), and quarter 4(October
December). The dependent variable was the total count of
small cetaceans captured during a given shing set.
We also examined the impact of pinger use on the
sherys target catch of sharks and rays. These tests also
employed GLMMs and were structured similarly to the tests
for small cetaceans described above. However, as shark and
ray catch data were highly overdispersed we included an
additional individual level random eect term that served to
t the extra-Poisson variation as a normally distributed
error around the intercept (Elston et al., 2001). The
dependent variable here was the total count of sharks and
rays captured during a given shing set.
Using the GLMMs we were able to calculate the small
cetacean and target catch for control and experimental sets.
This was accomplished by back-transforming the intercepts
of the control and treatment groups to derive the catch per
unit eort, which is presented as catch km
2
h
1
.
All GLMMs were tted using the lme4package for
Rv.2.13.1(R Development Core Team, 2011). Maps were
prepared using ArcMap v. 9.2(ESRI, Redlands, USA) and
the Hawths Tools Extension (Beyer, 2004). Bathymetric
values were obtained from the Global Bathymetric Chart of
the Oceans (IOC, IHO & BODC, 2003). Descriptive
statistics are presented as mean ±SD unless specied
otherwise. Trip costs and prots are presented in USD.
Results
Fishing effort
Over the 29 months of the study (April 2009August 2011)
we observed 195 control sets over 47 trips and 156
experimental sets over 43 trips (Table 1,Figs 1&2).
Blubber of small cetaceans taken from bycatch and
harpooned animals was used as bait in 24% of control sets
and 31% of experimental sets. The mean cost to provision
trips was USD 1,020 ±669 (range USD 2204,405,n552)
and average gross prots were USD 2,195 ±1,594 (range USD
07,401). Net prots were USD 1,176 ±1,468 (range USD
2,2766,094), with 10 trips (19.2%) operating at a loss.
Bycatch of small cetaceans
Five species of small cetaceans were observed captured,
including common dolphins (n 545), dusky dolphins
Lagenorhynchus obscurus (n 520), bottlenose dolphins
(n 525), Burmesiters porpoises Phocoena spinipinnis
(n 58) and pilot whales (n 52). Each of these species was
caught in both control and experimental sets, except pilot
whales, which were only caught on one occasion in a control
set. Forty-ve percent of all small cetacean bycatch was
common dolphins. All small cetaceans died as a result of
their entanglement. Larger bycatch, including bottlenose
dolphins and pilot whales, were typically discarded, whereas
the majority of dusky dolphins were butchered for use as
Using pingers to reduce bycatch 3
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bait and the majority of Burmeisters porpoises were
butchered for use as food (Table 2).
In addition to bycatch, 23 common dolphins and two
dusky dolphins were observed to be harpooned, for use as
bait on subsequent sets. This typically occurred as vessels
were travelling to the shing ground prior to the rst shing
set. Harpooning was infrequent, occurring on 10 trips (11%)
and with 14individuals per event and only on trips
primarily targeting blue and mako sharks. Twenty common
dolphins were harpooned during seven trips that used
pingers and two dusky dolphins and three common
dolphins were harpooned during three control trips.
Pinger effectiveness
A total of 100 small cetaceans were observed captured,
67 during control sets and 33 during experimental sets
Salaverry
79 W80 W81 W
7S
8S
9S
10 S
0 10050 km
PERU
1
0
0
0
m
2
0
0
m
5
0
0
m
2
0
0
0
m
FIG. 1 Locations of control (lled circles)
and experimental (open circles) shing
sets observed over the 29 months from
April 2009 to August 2011. Fishing vessels
participating in the study were based in
the port of Salaverry. The rectangle on
the inset indicates the location of the
main map in Peru.
Fishing sets
Quarter
FIG. 2 Distribution of control and experimental sets by monthly
quarters over the course of the study (April 2009 to August
2011). Q1, JanuaryMarch; Q2, AprilJune; Q3, JulySeptember;
Q4, OctoberDecember.
4 J. C. Mangel et al.
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(Tables 2&3,Fig. 3). Twenty-two percent of control sets (43
sets) and 16% of experimental sets (25 sets) had bycatch of
small cetaceans. Control sets had a maximum catch of four
individuals in a given set whereas experimental sets had a
maximum catch of three individuals. Sets using pingers had
a37.2% lower bycatch rate of small cetaceans and this
dierence was statistically signicant (GLMM, χ
2
1
54.0158,
P50.0450;Table 4,Fig. 4). The bycatch rate declined from
0.798 km
2
h
1
(range ±1SE 0.6780.939) for control sets to
0.502 km
2
h
1
(range ±1SE 0.4070.619) for experimental
sets. There were declines in bycatch rates of each small
cetacean species but none of these declines were statistically
signicant (Tables 3&4,Fig. 4).
Control sets had a target catch rate of 18.6sharks km
2
h
1
(range ±1SE 14.024.7) whereas experimental sets had a
catch of 26.3sharks km
2
h
1
(range ±1SE 19.735.0) but
this dierence was not statistically signicant (GLMM,
χ
2
1
52.9157,P50.088,Table 4,Fig. 5). Likewise, there
was no statistical dierence in the catch rates of rays
between control sets (GLMM, χ
2
1
50.0534,P50.82) and
experimental sets (Table 4,Fig. 5), with catch rates of
0.001 km
2
h
1
and 0.002 km
2
h
1
, respectively.
Discussion
Because of the nature of small-scale sheries (i.e. minimal
management or enforcement, economic and political
marginalization), eorts to identify, test and implement
bycatch mitigation measures have proven challenging
(Campbell & Cornwelles, 2008; Soykan et al., 2008). Here,
in the rst study of its kind in the south-eastern Pacic
Ocean, we tested pinger eectiveness and have shown that
they reduced bycatch of small cetaceans in the Peruvian
small-scale driftnet shery. As was observed in the
California drift gill-net shery for swordsh and sharks,
the reduction was most pronounced when assessing total
bycatch of small cetaceans (Barlow & Cameron, 2003).
Given the modest sample size in our study and the relative
rarity of bycatch events, the observed declines in bycatch at
the species level were not statistically signicant. Although
use of pingers did reduce the bycatch rate by 37%, it did
not eliminate it. The greatest decline in bycatch rate was
observed for common dolphins (44% decline), similar to the
c. 50% decline observed in the California drift gill-net
shery for 19902009 (Carretta & Barlow, 2011), but c. half
the 86% decline observed in a controlled pinger experiment
in the same shery for the period 19961997 (Barlow &
Cameron, 2003).
Pinger effectiveness
How pingers work to reduce small cetacean captures in nets
is still unclear (Kraus et al., 1997; Carlström et al., 2002;
Morton, 2002). The range at which these devices may
be audible is known to be variable and subject to
environmental conditions such as sea condition and water
TABLE 2 Species composition of bycatch of small cetaceans for control (no pingers) and experimental (with pingers) shing sets, and
percentage, by species, of nal use of the carcasses.
Species Total
Treatment Final use (%)
No pingers With pingers Discarded
1
Bait
2
Food
3
(n)
Delphinus spp. 45 33 12 41 44 12 34
Lagenorhyncus obscurus 20 11 9 32 58 0 19
Tursiops truncatus 25 16 9 67 33 0 18
Phocoena spinipinnis 8 5 3 43 0 57 7
Globicephala spp. 2 2 0 100 0 0 2
Total 100 67 33
1
Animals recovered dead and discarded at sea
2
Animals recovered dead and then butchered for use as bait during subsequent shing sets
3
Animals recovered dead and then butchered for food either for use during the trip or for home consumption
TABLE 3 Per set catch rates for all small cetacean bycatch species by control (no pingers) and experiment (with pingers) treatment groups.
Species
Control Experiment
0 12340 1234
Total bycatch 152 23 17 2 1 131 18 6 1 0
Delphinus spp. 171 16 7 1 0 145 9 2 0 0
L. obscurus 187 6 2 0 0 150 4 1 1 0
T. truncatus 186 4 3 1 1 149 6 1 0 0
P. spinipinnis 191 3 1 0 0 154 1 1 0 0
Globicephala spp. 194 0 1 0 0 156 0 0 0 0
Using pingers to reduce bycatch 5
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temperature (Trippel et al., 1999; Carlström et al., 2002).
Dolphins and porpoises have been shown to alter their
behaviour or distribution in the presence of pingers (Cox
et al., 2003; Carlström et al., 2009). Experiments with
Dukane 1000 pingers have indicated that they are probably
audible under favourable weather conditions at a range of
600 m (Trippel et al., 1999) and lead to reduced
echolocations in harbour porpoises Phocoena phocoena at
500 m (Carlström et al., 2009).
The appropriate spacing of pingers has been subject to
some debate and recommendations vary (Bordino et al.,
2002; Barlow & Cameron, 2003; Larsen & Krog, 2007; Gazo
km
(a) (b)
FIG. 3 Locations and quantities of small cetacean bycatch in (a) control and (b) experimental sets. The shaded area is the minimum
convex polygon of shing sets.
TABLE 4 Mean catch rates (km
2
h
1
, with range ±1SE, derived from the generalized linearmixed models used to test pinger eectiveness) of
bycatch (dolphins and porpoises) and target catch (sharks and rays) for all observed control (no pingers) and experimental (with pingers)
sets from April 2009 to August 2011, and % change in catch rate between control and experimental sets, and associated P-values.
Species
No pingers With pingers
% change PMean range ±1 SE Mean range ±1SE
Dolphins & porpoises
Total 0.798 (0.6780.939) 0.502 (0.4070.619) 37.2 0.045
Delphinus spp. 0.289 (0.2250.372) 0.160 (0.1140.226) 44.6 0.093
L. obscurus 0.048 (0.0290.080) 0.043 (0.0250.073) 10.4 0.827
T. truncatus 0.051 (0.0300.085) 0.031 (0.0170.056) 39.4 0.360
P. spinipinnis 0.001 (0.0000.009) 0.000 (0.0000.004) 75.0 0.379
Globicephala spp. 0.000 (0.0000.092) 0.000 100.0 0.692
Sharks & rays
Sharks 18.6 (14.024.7) 26.3 (19.735.0) 29.3 0.088
Rays 0.001 (0.0000.007) 0.002 (0.0000.009) 22.2 0.817
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et al., 2008; Gönener & Bilgin, 2009). Spacing has sometimes
been in excess of the manufacturers recommendations
(Larsen & Krog, 2007; Gazo et al., 2008; Gönener & Bilgin,
2009). We spaced pingers at 200 m apart in an attempt to
balance pinger eectiveness and the projects logistical
constraints. Pinger spacing was also of concern because the
relatively high costs of pingers in relation to income levels
in this shery had implications for economic viability,
implementation and monitoring. The 37% decrease in small
cetacean bycatch rate that we observed was less than that
observed in other studies, where reductions were c. 5090%
(Kraus et al., 1997; Bordino et al., 2002; Barlow & Cameron,
2003; Carretta et al., 2008; Carretta & Barlow, 2011). The
reasons for dierences between studies include variations
in shery characteristics and net type, target and
bycatch species, abundance and group size, and pinger
specications, as well as varying methods used to calculate
bycatch rates. There have also been declines observed in
pinger eectiveness between controlled studies and actual
implementation, including in the California driftnet shery
(Carretta & Barlow, 2011) and the US north-east gill-net
shery (Palka et al., 2008). Nevertheless, further reductions
in the bycatch rate of small cetaceans in Peru may be
possible with reduced pinger spacing, as there is evidence
that bycatch rates decrease as the number of pingers
increases (Trippel et al., 1999; Barlow & Cameron, 2003) and
that bycatch rates can increase in sets with less than the
prescribed number of operational pingers (Palka et al., 2008;
Carretta & Barlow, 2011).
We did not observe bycatch of pinnipeds, although
South American sea lions Otaria avescens and fur seals
Arctocephalus australis are common on the shing grounds
and are known to depredate catch from shing nets.
Concerns have been raised that the sound emitted by
pingers could increase depredations by pinnipeds by
alerting them to the presence of nets, commonly referred
to as the dinner belleect (Dawson, 1991). A review of
19 years of on-board observer data from the California
driftnet shery found evidence of an increase in depreda-
tions by pinnipeds after pingers were introduced but
attributed that increase to changes in target catch rates
and pinniped populations, rather than to attraction to the
net by the pingers (Carretta & Barlow, 2011). The systematic
monitoring of depredations by pinnipeds was beyond the
Lagenorhynchus obscurus
Tursiops truncatus
No pinger
Catch km2h–1 Catch km2h
1
Pinger
No pinger Pinger No pinger Pinger
No pinger Pinger
Phocoena spinipinnis
FIG. 4 Bycatch rates (catch km
2
h
1
), with SE bars, of the main four small cetacean species for control (no pinger) and experimental
sets (pinger).
Using pingers to reduce bycatch 7
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scope of our study as there was some uncertainty regarding
the ability to identify depredation events accurately and
consistently. It should, however, be monitored in the future
as the eectiveness of pingers could be undermined if catch
values declined as a result of increased damage from
pinnipeds and other species (Kraus et al., 1997; Bordino
et al., 2002; Carretta & Barlow, 2011).
There was no statistically signicant dierence in catch
rates of sharks and rays, the primary target species in this
shery, between control and experimental sets. This nding
is in line with other pinger trials that have shown either no
impact on target catch (Kraus et al., 1997; Trippel et al., 1999;
Bordino et al., 2002; Carlström et al., 2002; Gazo et al., 2008;
Gönener & Bilgin, 2009) or an improved target catch
(Buscaino et al., 2009). The lack of an impact in our study
is not unexpected as shark hearing is typically in the
40800 Hz range (Myrberg, 2001), well below the 10 KHz
fundamental frequency of the Dukane pingers. Moreover,
while sharks and small cetaceans are typically considered as
having a predatorprey relationship, given the species and
small sizes (c. 1m; ProDelphinus, unpubl. data) of sharks
typically captured in the shery it may be more accurate to
consider them as primarily competitors for prey (Heithaus,
2001).
Regional significance and barriers to implementation
The signicance of the declines in bycatch rate associated
with pinger use become clear when one considers the
potential regional-level impacts. Peruvian small-scale
sheries grew during 19952005 by c. 50%to9,667 vessels,
of which the largest component (30% of the eet) is gill-net
vessels (Escudero, 1997; Estrella et al., 1999,2000; Estrella &
Swartzman, 2010; Alfaro-Shigueto et al., 2011). The annual
mortality of small cetaceans in the operations of the
Peruvian small-scale driftnet eet is estimated to be
15,00020,000 (Mangel et al., 2010). Mortality of small
cetaceans for the port of Salaverry alone was estimated to
average 2,412 animals per annum for 20022007 (Mangel
et al., 2010). Given the catch rates reported here and the level
of annual shing eort for the port of Salaverry, c. 4,000 sets
(Mangel et al., 2010), one could expect a reduction in
bycatch of small cetaceans of c. 500 individuals per year if all
driftnet vessels from the port used pingers. As the Salaverry
gill-net eet represents c. 2% of gill-net shing eort in Peru
(Escudero, 1997; Estrella et al., 1999,2000; Estrella &
Swartzman, 2010; Mangel et al., 2010), and that eet deploys
at least 100,000 km of net annually (Alfaro-Shigueto et al.,
2010), use of pingers by gill-net vessels throughout Peru has
Shark & ray captures
0
1 - 50
51 - 100
101 - 200
>200
01
01
10
200
5
0
0
1
0
0
0
2
0
0
0
0100km
(b)
(a)
50
FIG. 5 Locations and quantities of shark and ray catch in (a) control and (b) experimental sets.
8 J. C. Mangel et al.
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the potential to reduce small cetacean mortalities by
thousands of animals each year.
Signicant barriers to implementation do, however, exist.
The current unit cost of commercially available pingers is
c. USD 130 per unit and the recommended spacing is
generally 200 m (Northridge et al., 2010). To equip a 2km
length net in this shery would require an investment of
c. USD 1,1001,500. As we report here, this is approximately
equivalent to the mean net protofashing trip. These
prots are divided between captain, crew and owner so the
portion left to fund the purchase of pingers would take
multiple trips to oset.
The pingers that are currently commercially available are
durable and typically have estimated battery lives of
thousands of hours to multiple years. These characteristics
are particularly important for utilization by a small-scale
eet, where vessels are numerous and dispersed among
many, often remote, locations. Under such conditions
pinger or battery replacements would be dicult to nd
and this could lead to increased failure to use pingers
appropriately. But there would still be unavoidable costs,
however small, associated with maintaining pingers (e.g.
battery replacement, pinger damage and loss). Whether
vessel owners in this shery would be willing to accept all
the costs associated with purchasing and maintaining
pingers in a management environment in which enforce-
ment is minimal is questionable. Small cetaceans are
still regularly captured, consumed and sold, in violation
of regulations (Van Waerebeek et al., 2002; Mangel
et al., 2010). Other than a new eort for regulation and
enforcement, which is unlikely, the available levers by which
to mandate pinger use are limited. As a result, promotion
and uptake of pinger use in the shery will probably begin
on a voluntary basis and build upon positive experiences of
other shers. In such situations product cost and ease of
use become important factors that could help determine
broader acceptance in the shery. As Alfaro-Shigueto et al.
(2010) note, gill-net sheries in Peru can be thought of as
entry-level or gatewaysheries because of their relatively
low costs and prots in comparison to other sheries such
as long-line sheries. Any eorts to promote pinger use
should therefore also stress the potential benets to work
eciency. Reduced net damage associated with pinger use
has been reported (Culik et al., 2001; Gazo et al., 2008;
Buscaino et al., 2009). Moreover, conrming the obser-
vation in Mangel et al. (2010), we found that c. 50% of all
bycatch of dolphins and porpoises was discarded, a
potential source of net damage and lost time and eort
associated with disentanglement.
The use of small cetaceans for bait is widespread globally
(Dolar, 1994; Goodall et al., 1994; Lescrauwaet & Gibbons,
1994; Zavala-Gonzalez et al., 1994; Mora-Pinto et al., 1995;
Van Waerebeek et al., 1997; Avila et al., 2008; Mangel et al.,
2010). We observed harpooning of dolphins for use as bait
on 11% of trips. There is clearly a need to continue
monitoring this dynamic as continued harpooning would
oset some of the gains made through pinger use. Under the
currently limited monitoring and enforcement of the ban
on capture and trade of small cetaceans, the regular use of
dolphins for bait will probably continue.
Conclusions and recommendations
We have shown that pingers were eective at reducing
bycatch of small cetaceans in the Peruvian small-scale
driftnet shark shery. Given the vast size of this shery and
its current levels of bycatch of small cetaceans (Alfaro-
Shigueto et al., 2010; Mangel et al., 2010) appropriate use of
pingers could result in mortality reductions of thousands of
individuals per annum and would represent an important
step for the conservation of small cetaceans in the south-
eastern Pacic. Further collaborative research with sher-
men and vessel owners in the Peruvian gill-net shery are
currently underway and will continue to monitor pinger
eectiveness and their impacts on small cetaceans and the
shery (e.g. target catch rates, depredations by pinnipeds).
As the pingers used in this study are no longer
commercially available, an alternative will have to be
found if larger-scale trials are to occur. The current suite
of commercially available pingers each has specic design
specications and are not necessarily inter-changeable, and
therefore their suitability for the Peruvian small-scale
driftnet shery needs to be assessed prior to large-scale
implementation.
Additional challenges to large-scale implementation
remain, including the costs associated with pingers and
their maintenance, and the continued practice of harpoon-
ing of dolphins for use as bait. These issues will have to be
addressed before expanding pinger use to the national level
and to achieve the full extent of potential reductions in
mortality of dolphins and porpoises.
Acknowledgements
We thank the participating shermen and eld observers
for their generous collaboration. ProDelphinus biologists
Natalia Ortiz and Graciela McEvoy helped with eld work.
Project funding and equipment was provided by Cetacean
Society International, Chelonia Ltd, Cleveland Metroparks
Zoo, Comisión Permanente del Pacíco Sur, the Darwin
Initiative, the Oak Foundation through Duke University, the
Ruord Foundation and the Whale and Dolphin
Conservation Society, as well as Dr Andy Read of Duke
University and Dr Per Berggren of Newcastle University.
The manuscript beneted from helpful comments by two
anonymous reviewers. JCM and JA-S are Overseas Research
and Students Awards Scheme (ORSAS) and University of
Using pingers to reduce bycatch 9
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Exeter scholarship awardees, respectively. MJW is funded
by the Peninsula Research Institute for Marine Renewable
Energy (PRIMaRE). DH is supported by the Natural
Environment Research Council and the European Union.
BJG receives funding from the Darwin Initiative, the Natural
Environment Research Council and the European Union.
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Using pingers to reduce bycatch 11
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Biographical sketches
JEFFREY MANGEL and JOANNA ALFARO-SHIGUETO operate the
Peruvian NGO ProDelphinus whose work focuses on monitoring and
mitigating the bycatch of threatened marine fauna in small-scale
sheries. MATTHEW WITT is researching spatial ecology as an aid to
understanding marine vertebrate distribution and foraging ecology.
DAVE HODGSON is a quantitative ecologist focusing on the robustness
of empirical models on population and community dynamics, with
applications for conservation management and the exploitation of
natural resources. BRENDAN GODLEY has wide-ranging interests in
biodiversity conservation and especially the study of marine vertebrates.
12 J. C. Mangel et al.
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Oryx
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... There have been several trials of bycatch mitigation measures in Peru's small-scale net fishery. Mangel et al. (2013) reported a 37% decline in the small cetacean bycatch rate using acoustic alarms (pingers). A reduction in Burmeister's porpoise acoustic activity in the presence of pingers was also reported (Clay et al., 2019). ...
... Another persistent and sizeable problem is the use of small cetaceans as bait in Peru's small-scale net and longline fisheries. This practice -documented since at least the early 1990s (Van Waerebeek et al., 1997) -entails the butchering of either incidentally caught or harpooned small cetaceans for use as bait on both net and longline vessels primarily targeting sharks (Campbell et al., 2020;Doherty et al., 2014;Mangel et al., 2010Mangel et al., , 2013. ...
... They include modifications to fishing gears, alternative materials for nets, and acoustic and visual deterrents (e.g. Mangel et al., 2013;Clay et al., 2019;FAO, 2018;Bielli et al., 2019;FAO, 2019;Queirolo et al., 2019). Some of these measures have already been tested in the region but political will and funding are needed to scale up such initiatives. ...
Article
With the entry into force of the Fish and Fish Products Import Provisions of the United States Marine Mammal Protection Act (MMPA), countries that export such products to the U.S. market could face significant challenges. Provisions include that fish and fish products exported to the U.S. must come from fisheries with a regulatory program comparable in effectiveness to the U.S. standard. Using three countries in the Southeast Pacific (Chile, Ecuador and Peru) as a case study, the potential economic impacts of the MMPA were analyzed. As a reference, in 2019, this region exported 389 thousand tons valued at US $3.2 billion to the USA in fish and aquaculture products, of which ca. 69% could become subject to commercial restrictions related to the MMPA. In the case of Chile, most exported fish products come from aquaculture, but in Ecuador and Peru they come from small-scale fisheries. Because of the associated costs that countries may incur to comply with MMPA requirements, moving in stages is recommended, first issuing regulatory reforms related to marine mammals protection, and then estimating bycatch rates for each species/population by fishery. Simultaneously, but as a medium-term goal, population estimates to define limits of biological removal should be conducted. Despite the progress in fishing management made by these three countries, with Chile at the forefront, it may still be a challenge for the export fisheries to achieve comparability findings under the MMPA. However, efforts and incentives offer new opportunities for conservation by reducing current levels of marine mammal mortality in fisheries and is already having benefits that could be enhanced if countries address with responsibility the impacts from fisheries on marine mammals populations in the region.
... These management strategies were developed and evaluated in the context of commercial fishery operations. The high economic and social costs of management, such as, heavy reliance on expensive technology, marginalization of fishing communities, inadequate governance and enforcement, limit their wider implementation in small-scale fisheries (Brotons et al., 2008;Mangel et al., 2013;Brownell et al., 2019) but these aspects were not explicitly considered in the Dawson et al. (2013) typology. ...
... Acoustic deterrent devices or pingers, actively emit mid to high frequency signals (2.5 to 10 kHz) at a low intensity (< 150 dB, 1 µPa at 1 m) that "deter" marine mammals from approaching fishing gear. Pingers have been shown to reduce the bycatch of bottlenose dolphins (Cox et al., 2004), harbor porpoises (Phocaena phocaeana) and Franciscana (Pontoporia blainvillei) (Dawson et al., 2013;Mangel et al., 2013;Chladek et al., 2020) in gillnet fisheries. Pingers have also proven successful in reducing pinniped interactions with aquaculture operations and have reduced the bycatch of some (but not all) species of cetaceans in gillnets (Clay et al., 2019). ...
Article
Full-text available
Marine mammal interactions with fisheries, such as bycatch and depredation, are a common occurrence across commercial and small-scale fisheries. We conducted a systematic review to assess the management responses to marine mammal interactions with fisheries. We analyzed literature between 1995 and 2021 to measure research trends in studies on direct and indirect interactions for: (i) high and low to middle-income countries, (ii) fishery operations (commercial and small-scale), and (iii) taxonomic groups. Management responses were categorized using the framework described previously in peer-reviewed studies. Marine mammal bycatch remains a major conservation concern, followed by marine mammal depredation of fishing gear. A high proportion of studies concentrated on commercial fisheries in high-income countries, with an increase in small-scale fisheries in low to middle-income countries between 1999 and 2020. The insufficient understanding of the social dimensions of interactions and the inevitable uncertainties concerning animal and human behaviors are major challenges to effective management. Despite the key role of human behavior and socioeconomics, we found only eight articles that incorporate human dimensions in the management context. Integrating social dimensions of marine mammal interactions with fisheries could help in setting pragmatic conservation priorities based on enhanced understanding of critical knowledge gaps. An area-specific adaptive management framework could be an effective tool in reducing the risk to marine mammals from fisheries by coupling technical solutions with socio-economic and political interventions. We conclude that despite the vast body of literature on this subject, a “silver bullet” management solution to marine mammal interactions with fisheries does not yet exist.
... Our method can be applied elsewhere than only in the Aegean Sea. For example significant fishing occurs off the coast of Peru, but studies of conflicts with cetaceans are relatively recent and still restricted to the identification of conflicts, while offering possible solutions without a large ecosystem analysis (Campbell et al., 2020;García-Godos et al., 2013;GFW, 2021a;Mangel et al., 2013). ...
Article
Increasing depletion of fish stocks in the Mediterranean Sea intensifies conflicts between fisheries and marine mammals, such as the common bottlenose dolphin (Tursiops truncatus, Montagu, 1821). To increase the knowledge of such interactions in the eastern Mediterranean Sea, fishing activities of commercial fisheries and biomass of fish families targeted by fisheries and T. truncatus were analysed to identify areas that are more likely to be affected by these conflicts in the Dodecanese region of Greece. The area with the highest risk of conflict is located between Kos and Leros islands and the southwest coast of Turkey, which is mainly caused by trawl fishing activities. The presence of Sparidae, Merlucciidae, Mullidae and other unspecified fish families increased the likelihood of conflicts. Our applied method and results can be used to improve fishing regulations and management to diminish similar conflicts elsewhere in the world.
... [10,11,108], respectively). ADD use on gillnets has reduced the bycatch of harbour porpoises, Franciscana (Pontoporia blainvillei) and common dolphins, for example, but trials with bottlenose, Australian snubfin (Orcaella heinsohni) and humpback dolphins (Sousa sahulensis) have yielded only subtle behavioural responses or otherwise equivocal results, suggesting that ADDs may be ineffective for bycatch mitigation in the more neophilic species [21,31,[109][110][111][112]. ...
Article
The prevalence of small cetacean (including dolphins, porpoises and small odontocete whales) bycatch in fisheries worldwide remains an ongoing conservation and welfare challenge. Various mitigation methods have been implemented in attempts to reduce bycatch. Two such methods involve gear modification: placement of Bycatch Reduction Devices (BRDs) within trawl nets, usually involving a physical barrier and an escape hatch; and, deployment of Acoustic Deterrent Devices (ADDs, ‘pingers’), typically placed on static nets and some trawl nets, to alert cetaceans to their presence and deter them from interacting with the gear. Despite their efficacy in reducing bycatch under certain circumstances, negative welfare impacts remain for individuals interacting with both BRDs and ADDs. Post-mortem analyses of small cetaceans caught in trawl gear, for example, illustrate the potential long-term effects of capture myopathies and cardiac damage sustained during the acute stress of entanglement, prior to and during escape through the BRD. Further, animals may become entangled in the bars, ropes or mesh of the BRD or escape hatch itself, and little is known of their post-release survival. ADD efficacy is typically fishery- and cetacean species-specific and, even where deemed a success at reducing bycatch, displacing animals from their optimal foraging habitat could negatively impact individual survival. Some species display equivocal responses to ADDs, while others may habituate to or be attracted to the sounds produced as they learn to associate it with food rewards, as they do in trawl fisheries, thereby reducing ADD efficacy and increasing the likelihood of entanglement. Here, we provide a synthesis of existing studies of these mitigation methods and discuss the associated welfare issues, where poor welfare negatively impacts an individual’s physical or mental state. We conclude that cetacean welfare considerations should become an integral part of decision-making in relation to bycatch globally.
... This effect was absent at 400 m. Similarly, studies on different dolphin, porpoise, and beaked whale species have reported optimistic results of bycatch reduction by pingers (Carretta et al., 2008;Gearin et al., 2000;Mangel et al., 2013;Palka et al., 2008). However, for the common bottlenose dolphin (Tursiops truncatus), a species with a wide behavioral diversity, the success of the pingers as deterrents is controversial (Buscaino et al., 2009;Cox et al., 2003). ...
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.
... Bycatch through entanglement may be as important for population trends in aquatic animals as for those in the marine realm (Mangel et al., 2013;Anderson et al., 2020;Tixier et al., 2021). For example, entanglement is cited as the primary source of conflict and a contributor to population declines for both the boto and tucuxi (Campbell et al., 2020), with the latter now listed as endangered on the IUCN Red List (da Silva et al., 2018;IUCN, 2020;Brum et al., 2021). ...
Article
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Conservation of freshwater biodiversity and management of human-wildlife conflicts are major conservation challenges globally. Human-wildlife conflict occurs due to attacks on people, depredation of fisheries, damage to fishing equipment and entanglement in nets. Here we review the current literature on conflicts with tropical and subtropical crocodilians, cetaceans and otters in freshwater and brackish habitats. We also present a new multispecies case study of conflicts with four freshwater predators in the Western Amazon: black caiman ( Melanosuchus niger ), giant otter ( Pteronura brasiliensis ), boto ( Inia geoffrensis ) and tucuxi ( Sotalia fluviatilis ). Documented conflicts occur with 34 crocodilian, cetacean and otter species. Of the species reviewed in this study, 37.5% had conflicts frequently documented in the literature, with the saltwater crocodile ( Crocodylus porosus ) the most studied species. We found conflict severity had a positive relationship with species body mass, and a negative relationship with IUCN Red List status. In the Amazonian case study, we found that the black caiman was ranked as the greatest ‘problem’ followed by the boto, giant otter and tucuxi. There was a significant difference between the responses of local fishers when each of the four species were found entangled in nets. We make recommendations for future research, based on the findings of the review and Amazon case study, including the need to standardise data collection.
... This effect was absent at 400 m. Similarly, studies on different dolphin, porpoise and beaked whale species have reported optimistic results of bycatch reduction by pingers (Carretta et al., 2008;Gearin et al., 2000;Mangel et al., 2013;. However, for the bottlenose dolphin, a species with a wide behavioral diversity, the success of the pingers as deterrents is controversial (Buscaino et al., 2009;Cox et al., 2003). ...
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
... Although some mitigation methods or devices such as acoustic and visual deterrents have been shown to reduce bycatch rates (e.g. Mangel et al., 2013;Bielli et al., 2020;Omeyer et al., 2020), most of them seem to work for some species and not others, which can be an issue when bycatch can affect multiple taxa at the same place and time. Moreover, the cost of the available mitigation devices is usually high and this limits their use, particularly in developing countries where bycatch is increasingly recognized to be a major problem (Brownell et al., 2019;Anderson et al., 2020). ...
Article
Cetacean bycatch in tuna drift gillnet fisheries has the potential to be significantly reduced at a relatively low cost for fishers. However, further research with an appropriate sampling design and a large sample size is required to confirm the efficacy of the proposed mitigation method. The acceptability and adoption of subsurface setting by fishers also needs to be further investigated. Despite some limitations, this preliminary study also highlights the importance of crew-based observer data as an alternative source of data when observers cannot be deployed on fishing vessels.
... Although some mitigation methods or devices such as acoustic and visual deterrents have been shown to reduce bycatch rates (e.g. Mangel et al., 2013;Bielli et al., 2020;Omeyer et al., 2020), most of them seem to work for some species and not others, which can be an issue when bycatch can affect multiple taxa at the same place and time. Moreover, the cost of the available mitigation devices is usually high and this limits their use, particularly in developing countries where bycatch is increasingly recognized to be a major problem (Brownell et al., 2019;Anderson et al., 2020). ...
Article
Full-text available
• Bycatch is the most significant threat to marine megafauna (sea turtles, marine mammals, elasmobranchs, seabirds) worldwide, and the leading cause of the decline of several cetacean species. The bycatch issue in the Indian Ocean is poorly understood, but high bycatch levels in gillnet fisheries have been documented for the past two decades, in both small-scale and semi-industrial fisheries. Unfortunately, methods to reduce bycatch are often unavailable, financially non-viable or socially unacceptable to fishermen. • Using a network of trained boat captains in the tuna drift gillnet fishery in the Arabian Sea, targeted catch and bycatch data were collected from 2013 to 2017 off the coast of Pakistan (northern Indian Ocean). Two fishing methods using multifilament gillnets were used: surface deployment and subsurface deployment (i.e. headline of net set below 2 m depth). • Predicted catch rates for targeted species did not differ significantly between the two fishing practices, although a drop in tuna (6.2%) and tuna-like (10.9%) species captures was recorded in subsurface sets. The probability of cetacean bycatch, however, was 78.5% lower in subsurface than in surface sets. • Cetacean bycatch in tuna drift gillnet fisheries has the potential to be significantly reduced at a relatively low cost for fishers. However, further research with an appropriate sampling design and a large sample size is required to confirm the efficacy of the proposed mitigation method. The acceptability and adoption of subsurface setting by fishers also needs to be further investigated. Despite some limitations, this preliminary study also highlights the importance of crew-based observer data as an alternative source of data when observers cannot be deployed on fishing vessels.
... To optimize effort in a full-scale trial, it is advisable to carry out a power analysis based on data gained in a pilot study. Previous studies have carried out fishing trials based on only rough estimates without conducting a power analysis (Bielli et al., 2020;Larsen et al., 2013;Larsen and Eigaard, 2014;Mangel et al., 2013), resulting in large numbers of hauls (between 195 and 864), which could have potentially been optimized. While these large datasets are certainly valuable, statistically robust and sometimes even necessaryother trials optimized based on a power analysis using observer data (Barlow and Cameron, 2003;Carlström et al., 2002;Gearin et al., 2000) have had similar effort needs due to low bycatch ratesa power analysis will facilitate experimental planning. ...
Article
Bycatch of protected species, particularly small cetaceans, in gillnets is a worldwide concern. One hypothesis for this is that echolocating cetaceans entangle because they do not perceive conventional gillnets as impenetrable barriers, owing to the gillnet's faint echo. A gillnet modified for improved acoustical visibility was tested in a first pilot trial in a commercial gillnet fishery targeting turbot (Scophthalmus maeoticus) on the Turkish Black Sea coast. This study is the first demonstration of the viability of using a gillnet equipped with small acrylic glass spheres to reduce bycatch of harbor porpoises in a commercial fishery and provides the basis for full-scale sea trials of the gear in commercial fisheries through a power analysis. In these pilot experiments, the focus lied on the handling of the gear and identification of requirements for a full-scale trial, but results include promising bycatch data for an endangered echolocating marine mammal (Phocoena phocoena) and no reduction in catch efficiency of a bottom-dwelling, vulnerable species (Raja clavata).
Conference Paper
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Fifteen fishing centres on the northern and central coasts of Peru, including large industrial fishing ports and smaller fish landing sites were surveyed for cetacean landings periodically over 29 months, from January 1999-May 2001. Monitoring effort, measured in port-days (pd), was for northern Peru 61pd (1999), 73pd (2000) and 19pd (2001); for the central coast, 24pd (1999), 7pd (2000) and 2pd (2001). Effort was largely opportunistic to other shore-based studies, but some was dedicated to cetaceans. We here document evidence for a minimum of 471 small cetaceans (310 identified to species) encountered in and around ports and landing beaches. Species composition of identifiable specimens include (% in triennium sample): Burmeister's porpoise Phocoena spinipinnis (42.6%), long-snouted common dolphin Delphinus capensis (24.2%), dusky dolphin Lagenorhynchus obscurus (20.6%) and bottlenose dolphin Tursiops truncatus (12.6%). The number of specimens tallied often were a composition of the visible fraction of animals landed that day plus remains of other animals butchered on earlier days, whence no per diem landing rates can be deduced. Moreover a dramatic change was noted in landing procedures contrasting with 1980s-90s. Depending on the port, entire cetacean carcasses were rarely landed for being illegal. New practices include butchering captured specimens at sea and landing concealed, filleted meat. Uses are still predominantly human consumption and bait for elasmobranch fisheries (both longline and gillnet). Important numbers of specimens were encountered in the form of meat and identification requires molecular genetic analysis. From now onwards, direct shipboard monitoring will be essential to estimate total mortality. Three Burmeister's porpoises (and 12 green turtles) were incidentally taken in artisanal bottom gillnets (10-18cm mesh size) in 10 supervised overnight fishing trips off northern Peru. Gillnets were set for a total duration of 163 hrs. Porpoise catch rate per hour of net soaking was 0.018 or 0.3 porpoises/boat/night. Data suggest that the predicted (Van Waerebeek, 1994) long-term relative decline of L. obscurus in catch composition continues, the cause for which is unknown.
Article
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By-catches include spinner dolphin Stenella longirostris, pantropical spotted dolphin S. attenuata (purse seines and driftnets); bottlenose dolphin Tursiops truncatus (bagnets and driftnets); Fraser's dolphin Lagenodelphis hosei, Risso's dolphin Grampus griseus, melon-headed whales, Peponocephala electra and pygmy killer whales Feresa attenuata. -from Author
Article
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This is the preliminary and the first study for understanding the effect of acoustic deterrent devices (pingers) on catch rates of fish (target turbot fish, Schophthalmus maeoticus and non target thornback ray, Raja clavata) and harbour porpoise (Phocoena phocoena) bycatch directly in the turbot gill net fishery in the Black Sea conditions. Sea trials carried out using Dukane NetMark™ 1000 pingers in an active (with pinger) and in a control (without pingers) turbot gill net between March 5 and April 2, 2006 off the Sinop Peninsula. The results showed that Dukane NetMark™1000 pingers have been significantly shown to be effective in reducing P. phocoena bycatch in turbot gill net fisheries without significantly affecting target and non-target fish size and catch. The habituation problem of the species should also be further investigated in the future. © Central Fisheries Research Institute (CFRI) Trabzon, Turkey and Japan International Cooperation Agency (JICA).
Article
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Since 1974, species of small cetaceans, fur seals, sea lions, sea birds and to some extent sea otters, have been taken deliberately each year for bait in the Chilean artisanal fishery. In recent years, three new trends are contributing to alleviate mortality pressure on marine mammals in Magellanes: a change in fisheries legislation, an increased diversification of the artisanal fishery and an increasing public awareness of the values of marine wildlife. -from Authors
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.