Responsible tuna fishing as a guarantee of sustainable future

Indian Ocean dolphin populations down by over 80% since the 1950’s due to drift gillnet use

Indian Ocean dolphin populations down by over 80% since the 1950’s due to drift gillnet use

The Indian Ocean’s dolphin populations may have declined by more than 80% since 1950 because of the use of drift gillnets to catch tropical tuna. So says a study[1] conducted by an international group of scientists in which Miguel Herrera, deputy manager of OPAGAC,[2] participated. It estimates that 4.1 million small cetaceans, fundamentally dolphins, were caught in drift gillnets as bycatch between 1950 and 2018.

The study concludes that dolphin populations in the Indian Ocean today add up to only 13% of the population estimated in 1980, despite restrictions since the use of drifting gillnets was prohibited by the United Nations in 1993. According to experts, this is due to factors such as the current high dolphin bycatch, approximately 175 dolphins per 1,000 tonnes of tuna. Even so, this figure is far from the 600 dolphins estimated for the late nineteen-seventies. The experts also say that dolphin bycatch numbers hit their historic high between 2004 and 2006, with approximately 100,000 dolphins per year; the number has now fallen to 80,000 per year.

The fleets that use drift gillnets catch 34% of the tropical tuna that comes from the Indian Ocean. That’s more than any other type of fishing method, including purse seining. The Spanish tuna fleet uses purse seines, which have registered no marine mammal bycatch deaths at all in recent years. According to the study, the fleets of nine countries account for approximately 96% of all cetacean bycatch in tuna gillnetting in the Indian Ocean. They are, in this order, Iran, Indonesia, India, Sri Lanka, Pakistan, Oman, Yemen, the United Arab Emirates and Tanzania.

Measures for an uncontrolled problem

The main problem with drift gillnets, the experts say, is that they vary between 100 metres and over 30 kilometres in length and between 5 metres and over 20 metres in depth. For this reason, in 2017 the IOTC passed a resolution prohibiting the use of drift nets over 2.5 kilometres long; the ban also extends to Exclusive Economic Zones as of this year. The European Union joined the UN’s 1993 prohibition of drift gillnets with its own prohibition for tuna fishing in 2002 and for the entire EU fleet in 2015.

This being so, the authors of the study call for improved management and control by flag states and the IOTC, fundamentally because of the lack of data on the activity of the majority of the gillnetting fleets. The specific measures recommended include setting gillnet fishing effort limitations, monitoring to ensure that gillnets are no more than 2.5 kilometres long and applying more-exhaustive control to onboard activity through a combination of human observers and electronic monitoring solutions.

Lastly, unlike drift netting, tuna seining registers practically zero bycatch mortality in the Indian Ocean, according to a study[3] the Spanish fleet presented to the IOTC in 2018. The study shows that in recent years seine fishing has contributed nothing to cetacean mortality, 0.15% to the mortality of sharks, skates and rays and less than 0.3% to the mortality of turtles.

These figures are due to the fleet’s having taken management measures that prohibit seining for tuna associated with cetaceans and having voluntarily applied the Good Practice Code verified by the AZTI institute of technology. The code is part of the Fishery Improvement Project (FIP) the WWF kicked off in 2016, and it has helped reduce shark mortality by around 10% and increase turtle survival by nearly 100%.

According to OPAGAC deputy manager Miguel Herrera, “The importance of developing coastal countries’ fleets in the Indian Ocean, their big catches and the lack of control mechanisms are the reasons the proliferation of drift nets has not been stopped. Turning this dire situation around will require extremely tight control plus investment in alternative fishing methods to get rid of the gear, which is so harmful to the marine environment. In 2023 it will have been 30 years since drift nets were prohibited by the UN, and it would be quite grave for the international community if measures like this were to continue to be ignored.”

[1] Cetacean bycatch in Indian Ocean tuna gillnet fisheries, published on Endangered Species Research

[2] Producers’ Organization of Large Tuna Freezers

[3] Assessing the Contribution of Purse Seine Fisheries to Overall Levels of Bycatch in the Indian Ocean


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