[MARMAM] Cetaceans and Indian Ocean tuna fisheries

Charles Anderson charles.anderson11 at btinternet.com
Sat Sep 20 04:14:37 PDT 2014


Dear Colleagues, 

The following report has just been published:


Anderson, R. C. (2014) Cetaceans and Tuna Fisheries in the Western and
Central Indian Ocean. IPNLF Technical Report 2, International Pole and Line
Foundation, London. 133 pages.


It is freely available from the website of the International Pole-and-Line
Federation (www.ipnlf.org). The direct link is:


With best regards, 

Charles Anderson

Maldives & UK


This report reviews information on interactions between cetaceans (whales
and dolphins) and tuna fisheries in the western and central Indian Ocean.
The average annual catch of tuna and related species in the Indian Ocean was
just over 1.5 million tonnes during 2008-12. Of this, almost 1.1 million
tonnes (71%) came from the western and central Indian Ocean. The main
fisheries for tuna and tuna-like species in the region are gillnet (40% of
reported catch during 2008-12), purse seine (26%), longline (12%), handline
and troll (11%) and pole-and-line (9%).


Major gillnet fishing nations include Iran, India, Sri Lanka, Pakistan, Oman
and Yemen. Cetacean bycatch must be large, but is poorly documented. A rough
estimation, based on the limited published information available, suggests
that something in excess of 60,000 small cetaceans might be taken as bycatch
each year. There is an urgent need for monitoring and management of these
fisheries including the development of mitigation methods to reduce cetacean
bycatch. Large-scale gillnetting on the high seas (using nets in excess of
2.5km length) is banned by both UN convention and IOTC resolution, but is
being carried out by Iran, Pakistan and possibly also other countries;
compliance is required. More generally, the large and still expanding
gillnet capacity within the region needs to be assessed, and if appropriate
either capped or reduced.


Purse seining in the western and central Indian Ocean is dominated by French
and Spanish fleets. An increasing proportion of sets is made on drifting
fish aggregating devices (FADs) but there has been, and continues to be, a
considerable number of sets made on free schools (i.e. non-FAD-associated
tuna schools). Most cetaceans do not regularly associate with FADs and the
major potential cetacean interactions are with free school sets. During
1981-1999, 9.6% of all sets were reported to have been made in association
with baleen whales, probably Bryde’s whales (Balaenoptera brydei). When
encircled, most whales are reported to escape by breaking through the net.
Mortality is unknown, but may have been of the order of 10s annually. The
association of free schools of large yellowfin tuna with dolphins (mostly
spotted dolphins Stenella attenuata and spinner dolphins Stenella
longrostris) is more contentious. This association (which is common in the
Eastern Tropical Pacific and is

exploited by the purse seine fishery there) has always been reported to be
rare in the western Indian Ocean. However, the tuna-dolphin association is
common in many coastal areas of the region and widespread in the high seas
of the western Indian Ocean north of 10°S. Setting on dolphin schools has
been also reported to be rare, but its true scale is questioned. Setting on
cetaceans has recently been banned by EU regulation (2007) and IOTC
resolution (2013), so cetacean bycatch and mortality should be much reduced
in the future. 100% coverage by international observers would be ideal.


Longline fisheries were dominated for several decades by East Asian nations,
but now increasing catches are made by coastal countries, notably India, Sri
Lanka and Seychelles. A major issue for longliners is depredation – removal
of bait and damage of hooked fish by sharks and cetaceans. Several species
of cetacean have been implicated, but the main one appears to be the false
killer whale (Pseudorca crassidens). There is also some entanglement of
cetaceans in longlines (likely following attempts at depredation).
Development of mitigation measures is on-going and needs to be continued. It
is possible that some longline fishermen are deliberately killing cetaceans.


Several coastal countries have handline fisheries for large yellowfin tuna,
which fishermen locate by their association with dolphins (mainly spotted
and spinner dolphins). There is anecdotal evidence that some dolphins are
hooked. Although they invariably break free or are released, the scale of
any post-release mortality or of sub-lethal impacts is unknown. From the
Maldivian pole-and-line fishery, there are reports of dolphins (probably
Indo-pacific bottlenose dolphins, Tursiops aduncus) taking fish attracted by
the lights used during night bait fishing. The scale and potential impacts
of these interactions require assessment.


There has been a widespread failure to monitor and manage cetacean bycatch
in Indian Ocean tuna fisheries, and to develop and implement mitigation
measures. The enormous, and still growing, gillnet capacity in the region
should be of particular concern. There is a need for increased observer
coverage of all fisheries, supplemented by electronic monitoring.
Fishery-independent surveys of cetacean distribution and abundance in the
western Indian Ocean are also required to inform management.


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