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Cetacean bycatch in Indian Ocean tuna fisheries: recent
updates and perspectives from the 13th Meeting of the
Working Party on Ecosystems and Bycatch of the Indian
Ocean Tuna Commission
Jeremy J. Kiszka1,2, Brendan Talwar3, Gianna Minton4, Tim Collins5 and Randall R. Reeves6
1 Department of Biological Sciences, Florida International University, North Miami, USA
2 Tropical Conservation Institute, Florida International University, Miami, USA
3 US Marine Mammal Commission, Washington DC, USA
4 Megaptera Marine Conservation, Wassenaar, the Netherlands
5 Wildlife Conservation Society, Ocean Giants Program, Bronx, New York, USA
6 Okapi Wildlife Associates, Hudson, Quebec, Canada
Contact email: jkiszka@fiu.edu
Abstract
Bycatch is the most significant threat to cetaceans around the world. However, the magnitude of bycatch is still
poorly known, particularly in certain ocean basins such as the Indian Ocean. Tuna fisheries, both industrial and
small-scale, are of major socioeconomic importance throughout the Indian Ocean. Published information
suggests that cetacean bycatch rates in this region are relatively low in pelagic longlines and in purse-seines.
However, the increasing use of drift gillnets, particularly in the northern Indian Ocean, is of concern.
Preliminary estimates have suggested that as many as 60,000 cetaceans are caught annually in gillnets in the
Indian Ocean. Further investigations are required to refine these estimates. The Indian Ocean Tuna Commission
(IOTC) is responsible for the management of tuna and tuna-like species. The IOTC’s Working Party on
Ecosystems and Bycatch (WPEB) reviews and analyzes information on non-target species. At its annual
meeting in September 2017 the WBEP formally acknowledged the importance of cetacean bycatch and adopted
a work plan that included this subject as a research priority. While a severe shortage of data remains, the stage is
set for collaboration with the IOTC on data collection and ultimately for mitigating bycatch in the region.
Cetacean bycatch in Indian Ocean tuna fisheries: an overview
The magnitude of cetacean bycatch in the Indian Ocean region is poorly known, and limited
research has been conducted so far in small-scale coastal (but see Kiszka et al. 2009, Temple
et al. 2018) and industrial open-ocean fisheries (e.g. Anderson 2014, Escalle et al. 2015).
Some bycatch is known to occur in most fisheries, and it could be the leading cause of the
decline of some populations of coastal cetaceans (e.g. Kiszka 2015, Cerchio et al. 2015).
Tuna fisheries, both industrial and small-scale, are of major socioeconomic importance
throughout the Indian Ocean. Industrial tuna fisheries are dominated by purse-seines and
pelagic longlines, whereas artisanal tuna fisheries involve the use of handlines, poles-and-
lines, and gillnets. Over the last two decades, there has been an increasing number of studies
suggesting that cetacean bycatch rates are low in industrial tuna fisheries in the Indian Ocean
(Romanov 2002, Wang and Liu 2010, Sabarros et al. 2013, Escalle et al. 2015). Bycatch in
pelagic longlines is relatively rare and occasionally involves large depredating delphinids
(e.g. Globicephala macrorhynchus, Grampus griseus, Pseudorca crassidens), particularly in
the western tropical Indian Ocean (Poisson et al. 2001, Sabarros et al. 2013, see Kiszka 2015
for a review). Areas of high co-occurrence between cetaceans and purse seine fisheries have
been identified, particularly east of the Seychelles (December to March) and in the
Mozambique Channel (April and May; Escalle et al. 2015). However, relatively low bycatch
rates have been reported, particularly for pantropical spotted dolphins (Stenella attenuata)
and large balaenopterids such as humpback whales (Megaptera novaeangliae) and sei whales
(Balaenoptera borealis) (Romanov 2002, Escalle et al. 2015). Nevertheless, further
investigation is needed to assess the magnitude of cetacean bycatch in Indian Ocean purse-
seine and pelagic longline fisheries, particularly since 100% observer coverage should soon
be available (IOTC, personal communication, September 2017).
The rise of gillnet fisheries in the Indian Ocean
At least 21 countries are engaged in drift gillnet fishing in the Indian Ocean Tuna
Commission (IOTC) area of competence (Aranda 2017; IOTC data), and Indian Ocean tuna
drift gillnet fisheries contribute to the catches attributed to 6 countries in the IOTC area
(MRAG 2012). The fleets are mostly based in India, Iran, Indonesia, Pakistan, Sri Lanka,
Yemen, and Oman (Aranda 2017). The prevalence of artisanal fishing throughout this region
underlines the great uncertainty about the scale of bycatch, particularly in gillnet fisheries.
Drift gillnet fishing in the Indian Ocean is not yet officially defined as semi-industrial and
therefore it is not subject to the same restrictions as are applied to industrial vessels (Vessel
Monitoring System and restrictions on fishing capacity). The inability to enforce controls on
the high seas and in national EEZs, the relative ease of entry to gillnet fishing and the ability
of gillnet fishermen to sell their relatively low-quality catch in local markets all tend to
encourage the expansion of the artisanal and semi-industrial sectors, which are dominated by
gillnetting (Aranda 2017).
The number of gillnet fishing boats has been increasing for several years (Fonteneau 2011),
likely due, at least in part, to the low cost of operating gillnets compared to other gears. IOTC
nominal catch data suggest that artisanal fisheries are expanding, while industrial fisheries are
declining (Aranda 2017; Fig. 1).
Fig. 1: Annual trends in nominal tuna catches in the IOTC area of competence between 2000
and 2015 (source: IOTC nominal catch database; Aranda 2017).
Gillnet fisheries contribute about 35% of nominal IOTC catches, and this proportion
continues to increase, raising concern over the potential effects of bycatch on cetaceans and
other marine megafauna in the region, including elasmobranchs, sea turtles and a diversity of
large fishes. Anderson (2014) suggested that about 60,000 cetaceans were caught every year
in the western and northern Indian Oceans, including 24,000 off Iran, 10,000 off India and
7,000 off Pakistan. However, these estimates were preliminary and based on extrapolations
from a limited number of fisheries.
The IOTC
The IOTC is an intergovernmental Regional Fisheries Management Organization (RFMO)
which is responsible for the management of tuna and tuna-like species in the Indian Ocean.
The creation of the IOTC was approved by the Council of the Food and Agriculture
Organization (FAO) of the United Nations in 1993. The agreement is open to countries
bordering and/or fishing in the Indian Ocean, and there are currently 32 member states. The
Commission includes several subsidiary bodies: the compliance committee, the standing
committee on administration and finance, and the scientific committee. The scientific
committee meets annually and provides advice to the Commission on the status of stocks and
the management actions necessary to ensure the sustainability of fisheries. Several working
parties have been created to analyze problems related to the Commission’s management
goals, and they usually provide technical solutions to the scientific committee for
management recommendations to the Commission.
The IOTC Working Party on Ecosystems and Bycatch
The Working Party on Ecosystems and Bycatch (WPEB) annually reviews and analyzes
information on non-target species affected by Indian Ocean tuna fisheries (particularly
sharks, sea turtles, seabirds and cetaceans).
The IOTC-WPEB last met from 4-8 September 2017 in San Sebastian, Spain in order to
adopt policy recommendations and agree upon future priorities. While the primary focus was
assessment of the blue shark (Prionace glauca) stock in the IOTC Area of Competence, some
time was devoted to other bycatch species as well as ecosystem-based fishery management
initiatives.
The stated goals for the 2017 WBEP Meeting relative to marine mammals were to “Review
new information on marine mammal biology, ecology, fisheries interactions and bycatch
mitigation measures (all); Develop management advice on the status of marine mammal
species (all).” Prior to the 2017 meeting, the IOTC had no documentation expressing a need
for marine mammal bycatch mitigation or assessment. Papers had been presented on these
issues irregularly, but no formal recommendations had ever been developed. A report
presented by Kiszka et al. (2017) highlighted marine mammal bycatch interactions in the
Indian Ocean with a particular focus on the threat posed by tuna gillnet fisheries. By the
conclusion of the 2017 WBEP meeting, the importance of considering marine mammal
bycatch (particularly of cetaceans) had been clearly expressed and work plans as well as
research priorities had been formally adopted (see below). While there remains a lack of data,
the stage is now set for further collaboration on data collection with the IOTC and ultimately
for mitigating bycatch in the region.
The following text was included in the report of the 2017 IOTC WBEP Meeting (IOTC WPEB
2017):
1.1 Marine'mammals'
1.1.1 Review( new( information( on( marine( mammal( biology,( ecology,( fisheries(
interactions(and(bycatch(mitigation(measures'
1. The WPEB NOTED paper IOTC–2017–WPEB13–40 which provided an updated review on
the bycatch of marine mammals in the western Indian Ocean, including the following
abstract provided by the authors:
“Here we review available information on cetacean bycatch in all commercial
fisheries known to occur in the western Indian Ocean. In coastal waters of the
region, the magnitude of bycatch has only been quantified for driftnets targeting
large pelagic fish off Zanzibar. Based on bycatch levels and abundance of coastal
dolphins, it has been shown that the removals are unsustainable, particularly for
Indo-Pacific bottlenose dolphins (Tursiops aduncus) and Indian Ocean humpback
dolphins (Sousa plumbea). Elsewhere in the region, bycatch is known to involve
other species as well, including coastal, oceanic and migratory species such as
humpback whales (Megaptera novaeangliae), mostly in bottom-set and drift
gillnets. In open-ocean fisheries, bycatch in pelagic longlines has particularly
involved small and medium-sized delphinids (Globicephala macrorhynchus,
Grampus griseus, Tursiops truncatus, Pseudorca crassidens, Stenella spp.)
although data are sparse. In tuna purse- seine fisheries, captain logbooks (1980-
2011) and observer data (1995-2011) recorded high co- occurrence with cetaceans,
particularly east of the Seychelles (December to March) and in the Mozambique
Channel (April and May). However, few cetacean deaths were reported. Captures
of large whales (Balaenoptera spp.) in purse-seines in the western tropical Indian
Ocean have been reported. This review also presents information on bycatch in
coastal and offshore tuna gillnets from various locations. Overall, cetacean bycatch
is very poorly documented in the region and more systematic assessment is critical,
particularly for those fisheries that use gear known to entangle or entrap cetaceans.”
(see paper for full abstract)
2. The WBEP RECALLED Resolution 13/04 On the conservation of cetaceans, which includes
data collection and reporting requirements at the species-specific level, where possible, and the
banning of intentional sets on marine mammals. Although these are mandatory requirements for
all CPCs there is still a lack of data regarding species-specific marine mammal bycatch in the
IOTC Area of Competence, particularly for tuna gillnet fisheries where interactions are of
particular concern.
3. The WBEP NOTED the vulnerability of marine mammals to population decline after relatively
few fishery interactions due to their highly conservative life histories and, at times, demographic
isolation.
Family
Common name
Species
IUCN Red
List status
Interactions
by Gear
Type*
Balaenidae
Southern right whale
Eubalaena australis
LC
GN
Balaenopteridae
Common minke whale
Balaenoptera acutorostrata
LC
GN
Antarctic minke whale
Balaenoptera bonaerensis
DD
GN
Sei whale
Balaenoptera borealis
EN
PS
Bryde's whale
Balaenoptera edeni/brydei
DD
PS, GN
Blue whale
Balaenoptera musculus
EN
PS
Fin whale
Balaenoptera physalus
EN
PS
Omura's whale
Balaenoptera omurai
DD
PS
Humpback whale
Megaptera novaeangliae
LC**
PS, GN, LL
Physeteridae
Sperm whale
Physeter macrocephalus
VU
GN, LL
Kogiidae
Pygmy sperm whale
Kogia breviceps
DD
GN, LL
Dwarf sperm whale
Kogia sima
DD
GN, LL
Ziphiidae
Arnoux's beaked whale
Berardius arnuxii
DD
Unknown
Southern bottlenose whale
Hyperoodon planifrons
LC
Unknown
Longman's beaked whale
Indopacetus pacificus
DD
GN
Andrew's beaked whale
Mesoplodon bowdoini
DD
Unknown
Blainville's beaked whale
Mesoplodon densirostris
DD
Unknown
Gray's beaked whale
Mesoplodon grayi
DD
Unknown
Hector's beaked whale
Mesoplodon hectori
DD
Unknown
Deranigala's beaked whale
Mesoplodon hotaula
NA
Unknown
Strap-toothed whale
Mesoplodon layardii
DD
Unknown
True's beaked whale
Mesoplodon mirus
DD
Unknown
Spade-toothed whale
Mesoplodon traversii
DD
Unknown
Shepherd's beaked Whale
Tasmatecus shepherdi
DD
Unknown
Cuvier's beaked whale
Ziphius cavirostris
LC
GN
Delphinidae
Common dolphin
Delphinus delphis
LC
GN
Pygmy killer whale
Feresa attenuata
DD
GN
Short-finned pilot whale
Globicephala macrorhynchus
DD
LL, GN
Long-finned pilot whale
Globicephala melas
DD
Unknown
Risso's dolphin
Grampus griseus
LC
LL, GN
Fraser's dolphin
Lagenodelphis hosei
LC
GN
Irrawaddy dolphin
Orcaella brevirostris
VU
GN
Australian snubfin dolphin
Orcaella heinshoni
NT
GN
Killer whale
Orcinus orca
DD
LL, GN
Melon-headed whale
Peponocephala electra
LC
LL, GN
False killer whale
Pseudorca crassidens
DD
LL, GN
4. The WBEP NOTED that limited data indicate declines for several marine mammal species in the
Indian Ocean (e.g. Indian Ocean humpback dolphins Sousa plumbea, Indo-Pacific humpback
dolphin Sousa chinensis, Indo-Pacific bottlenose dolphin Tursiops aduncus) and that capture in
tuna gillnet fisheries is an important source of mortality. The WBEP REQUESTED that CPCs
collect data on the effectiveness of mitigation techniques intended to reduce bycatch in these
fisheries and implement successful mitigation strategies.
5. The WBEP NOTED the likelihood of gillnet entanglement on the high seas, particularly during
IUU fishing, where gillnets of greater than 2.5 km could still be in use.
6. The WBEP REQUESTED the Chair and the IOTC Secretariat begin discussions on the potential
for collaboration with the International Whaling Commission and other national and international
institutions to facilitate capacity building within CPCs regarding the establishment of marine
mammal bycatch mitigation programs.
1.1.2 Development(of(management(advice(on(the(status(of(marine(mammal(species'
7. The WPEB NOTED that to-date there has been no advice developed by the WPEB for marine
mammals, however, the WPEB AGREED that cetacean bycatch assessment and mitigation is an
important issue for consideration.
8. Therefore, the WPEB ADOPTED the management advice developed for cetaceans, as provided
in the draft status summary and REQUESTED that the IOTC Secretariat update the draft stock
status summary with the latest 2016 interaction data, and for the summary to be provided to the
SC as part of the draft Executive Summary, for its consideration:
Delphinidae
Indo-Pacific humpback
dolphin
Sousa chinensis
VU
GN
Indian Ocean humpback
dolphin
Sousa plumbea
EN
GN
Australian humpback
dolphin
Sousa sahulensis
VU
GN
Pantropical spotted
dolphin
Stenella attenuata
LC
PS, GN, LL
Striped dolphin
Stenella coeruleoalba
DD
GN
Spinner dolphin
Stenella longirostris
DD
PS, GN, LL
Rough-toothed dolphin
Steno bredanensis
LC
LL, GN
Indo-Pacific bottlenose
dolphin
Tursiops aduncus
DD
GN
Bottlenose dolphin
Tursiops truncatus
LC
LL, GN
Phocoenidae
Indo-Pacific finless
porpoise
Neophocaena phocaenoides
VU
GN
* Documented mortality within the IOTC area of competence is in bold.
** Arabian Sea population: EN
IUCN Red List of Threatened species. Version 2017-01. <www.iucnredlist.org>.
Downloaded on 6 September 2017.
• Cetaceans (Appendix XVII).
The following text was adopted by the IOTC Scientific Committee. This is the first Executive
Summary specifically directed at marine mammals and is expected to be the foundation for
marine mammal research and bycatch mitigation discussions at future IOTC meetings.
EXECUTIVE SUMMARY: CETACEANS
Status of cetaceans in the Indian Ocean
TABLE 1. Cetaceans: IUCN Red List status and records of interaction (including
entanglements and, for purse seines, encirclements) with tuna fishery gear types for all cetacean
species that occur within the IOTC area of competence.
INDIAN OCEAN STOCK – MANAGEMENT ADVICE
Stock status. No assessment has been undertaken by the IOTC WPEB for cetaceans due to the
lack of data being submitted by CPCs. However, the current International Union for
Conservation of Nature (IUCN) Red List status to date for each of the cetacean species reported
in the IOTC Area of Competence is provided in Table 1. Information on their interactions with
tuna fisheries in the IOTC is also provided. It is important to note that a number of international
global environmental accords (e.g. Convention on Migratory Species (CMS), Convention on
Biological Diversity (CBD), International Whaling Commission (IWC)), as well as numerous
fisheries agreements obligate States to provide protection for these species. The status of
cetaceans is affected by a range of factors such as direct harvesting (documented for several
countries, e.g. Sri Lanka, Indonesia, Madagascar and the Seychelles) and habitat degradation,
but the level of cetacean mortality due to capture in tuna drift gillnets is likely to be substantial
and is also a major cause for concern (Anderson 2014). Many reports (e.g. IOTC-2013-
WPEB07-37) also suggest some level of cetacean mortality for species involved in depredation
of pelagic longlines, and these interactions need to be further documented throughout the IOTC
Area of Competence. Recently published information suggests that the incidental capture of
cetaceans in purse seines is low (e.g. Escalle et al. 2015), but should be further monitored.
Outlook. Resolution 13/04 On the conservation of cetaceans highlights the concerns of the
IOTC regarding the lack of accurate and complete data collection and reporting to the IOTC
Secretariat of interactions and mortalities of cetaceans within tuna fisheries in the IOTC Area
of Competence. The IOTC adopted that CPCs shall prohibit their flagged vessels from
intentionally setting a purse seine net around a cetacean if the animal is sighted prior to the
commencement of the set. The IOTC also adopted that CPCs using other gear types targeting
tuna and tuna-like species found in association with cetaceans shall report all interactions with
cetaceans to the relevant authority of the flag State. It is acknowledged that the impact on
cetacean populations from fishing for tuna and tuna-like species may increase if fishing
pressure increases (which is already demonstrated for tuna gillnet fisheries) or if the status of
cetacean populations worsens due to other factors such as an increase in external fishing
pressure or other anthropogenic or climatic impacts.
The following should be noted:
• The number of fisheries interactions involving cetaceans is highly uncertain and
should be addressed as a matter of priority as it is a prerequisite for the WPEB to
determine a status for any Indian Ocean cetacean species.
• Available evidence indicates considerable risk to cetaceans in the Indian Ocean,
particularly from tuna drift gillnets (Anderson 2014)
• Current reported interactions and mortalities are scattered, but are most likely
severely underestimated.
• Maintaining or increasing fishing effort in the Indian Ocean without appropriate
mitigation measures in place will likely result in further declines in a number of
cetacean species. An increasing effort by tuna drift gillnet fisheries has been
reported to the IOTC, which is a major cause of concern for a number of species,
particularly in the northern Indian Ocean.
• Appropriate mechanisms should be developed by the Compliance Committee to
ensure CPCs comply with their data collection and reporting requirements for
cetaceans.
The following text was adopted by the IOTC WBEP Program of Work, which provides an
outline of requests for funding and management of project timelines for the IOTC Scientific
Committee. Essentially, IOTC work will not take place unless it appears on this Program.
CETACEANS
8.1 Review and development of cetacean bycatch
mitigation measures
Priority
8.1.1 Historical data mining for key species interacting
with IOTC fleets (e.g coastal gillnet, longline fisheries)
High
8.1.2 Creation of identification cards for cetacean
species in IOTC Area of Competence
High
8.1.3 Conduct ecological risk assessments for
cetaceans
High
8.1.4 Assess marine mammal bycatch interactions,
develop marine mammal bycatch standards, and
support mitigation efforts through collaborative
partnerships
Very High
Conclusions
Gillnet bycatch in the Indian Ocean remains poorly quantified, but likely poses a major threat
to cetacean populations, particularly in the coastal fisheries of all countries, and in offshore
tuna drift gillnet fisheries. There is a clear need for greater inter-governmental and inter-
organizational collaboration to accurately assess and address cetacean bycatch in Indian
Ocean fisheries. Current protections for cetaceans in the Indian Ocean are patchy at best. The
International Whaling Commission (IWC) established the Indian Ocean Sanctuary in 1979 to
protect whales from whaling. The sanctuary still exists, but currently does nothing to mitigate
fisheries bycatch, a significant modern threat to all cetaceans.
While the IWC is limited in its ability to influence fishing practices, a bycatch mitigation
initiative is ongoing and includes plans to collaborate with other intergovernmental
organizations. Among the recommendations of the IWC Scientific Committee at its 2017
annual meeting were the following (IWC 2017):
• Support the IOTC to encourage and help member states more effectively implement
the UN and IOTC resolutions banning large-scale, high-seas drift-net fishing (nets
greater than 2.5 km in length).
• Support the IOTC and other regional bodies in efforts to implement cetacean bycatch
data collection and reporting protocols.
Given the limited data, improvements in bycatch data collection, particularly in drift gillnets,
are greatly needed. The IOTC’s production and distribution of identification cards in 2018 to
improve species identification onboard vessels should have a positive effect on data
collection and reporting.
Acknowledgements
J. Kiszka and B. Talwar thank the US Marine Mammal Commission for providing financial
support to attend the 13th Working Party on Ecosystems and Bycatch.
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