@article{,

title = {Cetaceans and tuna fisheries in the Western and Central Indian Ocean},

author = {Anderson, R Charles},

url = {http://www.fao.org/3/a-bg252e.pdf},

year  = {2014},

date = {2014-01-01},

journal = {International Pole and Line Federation Technical Report},

volume = {2},

number = {10},

pages = {133},

abstract = {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.},

keywords = {Arabian Sea, Bycatch, cetaceans, Fisheries, Gill net, mitigation, Northern Indian Ocean, Regional management units, Tuna},

pubstate = {published},

tppubtype = {article}

}