The report entitled “Cetaceans and Tuna Fisheries in the Western and Central Indian Ocean” by Dr Charles Anderson was commissioned by the International Pole & Line Foundation (IPNLF) as part of its commitment to evidence-based research on fishery issues.
Some 1.1 millions tonnes of tuna and related species were caught annually between 2008-2012 in the western and central Indian Ocean, with reported catch during this time period split between gillnet (40 per cent ), purse seine (26 per cent ), longline (12 per cent ), handline and troll (11 per cent ) and pole-and-line (nine per cent ).
No fishery is completely exempt from cetacean interactions, but the extent of bycatch varies widely between fishing methods.
“The enormous, and still growing, gillnet fishery in the region should be of particular concern,” says Dr Anderson.
There has been no previous regional bycatch estimate, but it is likely that more than 60,000 cetaceans are killed annually in the western and central Indian Ocean by tuna gillnet fishing nations including Iran, India, Sri Lanka, Pakistan, Oman and Yemen. The report also highlighted that Iran, Pakistan and potentially other countries are carrying out illegal, unreported and unregulated (IUU) large-scale gillnetting on the high seas, banned by both UN convention and IOTC resolution.
For purse seine and longline tuna fisheries, the extent of cetacean mortality is also unclear. The Spanish- and French-dominated purse seine industry in the Indian Ocean not only sets nets near drifting fish aggregating devices (FADs), which appear to have limited cetacean interactions, but also regularly sets on so-called free schools of tuna, which may associate with cetaceans.
During early 1980s to late 1990s, close to 10 per cent of purse seine sets were made in association with baleen whales – the actual mortality is unknown. In addition, tuna-dolphin associations are common in many coastal areas of the western Indian Ocean and are widespread in the high seas north of 10°S; the extent of interactions with the purse seine fleet are questioned. Longline fisheries were found to have some instances of entanglement of cetaceans, due to their attraction to both bait and hooked tunas.
While hand line and pole-and-line tuna fisheries are also featured, the impact of their activities on cetaceans appears to be minimal.
“The implication of this report is that there are unknown interactions with cetaceans and tuna fisheries, hitherto unappreciated, which are important to consider in assessments of fisheries for their environmental performance,” says Dr Shiham Adam, Chair of the Scientific and Technical Advisory Committee of IPNLF.
IPNLF are working in collaboration with member fisheries to advance research, monitoring and management of such cetacean interactions; a newly appointed Fisheries Science Research Officer is advancing such work in the Maldives.
Dr Anderson commented: “Tuna fisheries are having a profound, and in some cases disastrous, impact on the whale and dolphin populations of the tropical Indian Ocean. However, there has been a widespread failure to monitor cetacean bycatch and even to enforce existing regulations, let alone attempt to reduce mortality. There are many issues, and few easy solutions, but there is no doubt that real progress can be made if there is the will to act.”
