When the Indian Ocean Tuna Commission’s scientific committee presented its latest findings on 2 December 2024 at an upscale hotel and conference centre complex in Cape Town, South Africa, many scientists were stunned.
The committee, led by Toshihide Kitakado and Gorka Merino, announced that stocks of yellowfin tuna, one of the world’s most prized varieties whose market is worth billions of dollars a year, was no longer considered overfished or subject to overfishing. Its status was changed from red to green, with an 89% probability that stocks had recovered.
In practical terms, the decision was the first step in allowing international fleets to catch more of the valuable fish.
This declaration, coming from an intergovernmental body responsible for managing tuna stocks in the Indian Ocean, shocked outside experts. If the assessment was wrong, as several leading marine scientists believe, the consequences could drastically affect the lives of millions of people and damage the long-term health of the ocean. “I thought that it must be some kind of miracle,” says Iris Ziegler, head of fisheries policies and ocean advocacy at the German Foundation for Marine Conservation (DSM), who attended the Cape Town meeting. “It really did not make sense.”
From red to green
In 2015, the scientific committee of the Indian Ocean Tuna Commission (IOTC) had declared yellowfin tuna (Thunnus albacares) “overfished”, with 94% certainty, and called for annual fishing to be cut by 20% to give populations a chance to recover. Yet every year for the following decade, global fleets caught more yellowfin than the level deemed sustainable by scientists.
The term “overfished” means the total biomass of a fish is below a determined limit. The term “overfishing” indicates the current level of fishing may result in a species becoming overfished, if it is not already.
Between 2018 and 2022, an average 429,421 tonnes of yellowfin were caught each year according to a 2023 IOTC scientific committee report, which relies on catch figures submitted by the crews themselves. This far exceeds the maximum sustainable yield (MSY) of 349,000 tonnes that this committee recommended.
MSY is a common metric in fisheries, used to estimate the largest amount of fish that can be sustainability caught over time. Catch limits are set for individual countries, although when contacted by Dialogue Earth, the IOTC did not provide any examples of action being taken against those who exceed these limits.
Despite this apparent sustained overfishing, by 2024 IOTC scientists were saying this species was in a healthy state.
So, did yellowfin stocks suddenly become markedly healthier? Were the decade’s preceding estimates wrong? Or was the new assessment far from the reality of what was in the ocean?
Independent scientists, civil society organisations and environmental campaigners tell Dialogue Earth the shift is due to highly controversial changes in the methodology used to calculate tuna population trends. Some claim it is an example of the European Union’s powerful, billion-dollar fishing lobby exerting its influence over authorities to allow its fleets to catch more yellowfin. They say profits for Europe are coming at the cost of food security, biodiversity and the livelihoods of small-scale fishers in Africa and Asia – fishers who depend on tuna for food and income.
“It’s all about profit,” says John Burton, founder of the UK-based sustainable fishing nonprofit SFACT. “Stocks have been deep in the red for years, then suddenly they turn green. It is in the interests of the EU. They are the pirates of the Indian Ocean.”
In response to the criticisms, one of the IOTC scientists involved tells Dialogue Earth the system is robust and was not influenced by lobbyists. In addition, a fishing industry representative insists the whole process is rigorous.
An ocean of tuna?
The Indian Ocean, which is bordered by Africa, Asia and Australia, is the world’s second largest tuna producing region. About 920,000 tonnes of the various species are caught there annually. This represents over a fifth of the world’s supply and is worth USD 2.3 billion, according to a 2023 study.
Yellowfin – a torpedo-shaped predator named for its bright yellow dorsal fin – accounts for a significant amount of the region’s tuna catch. Most is caught by industrial ships using purse seine and baited hook longline methods, for the canned tuna and sashimi markets.
The rare sight of a jumping yellowfin tuna in the Maldives, south-west of India in the Indian Ocean (Image: Anthony Pierce / Alamy)
Yellowfin biomass declined globally by 54% between the 1950s and 2020, according to a global study in 2023. The greatest decline over that period – 70% – was in the Indian Ocean, where the researchers concluded the species is in “dire straits”. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species rates yellowfin tuna globally as not particularly threatened. However, scientists who assessed the Indian Ocean population using the same IUCN methodology concluded it was “vulnerable”.
Conservationists warn a collapse in the yellowfin population could have serious repercussions for Indian Ocean ecosystems, where tuna play a key role as a top predator. It would also be devastating for the tens of millions of people in coastal areas who rely on fisheries for their livelihoods.
“If unsustainable yellowfin fishing continues, it could have permanent and extremely damaging effects on millions of people and the planet,” says Umair Shahid, the World Wide Fund for Nature’s (WWF) Indian Ocean tuna manager.
Shahid urges caution over the 2024 assessment: “While the assessment shows encouraging biological trends, WWF does not interpret this as a license to increase fishing pressure. On the contrary, we emphasise the need for structural reform, better data and long term ecosystem-based strategies to ensure the recovery is sustained and resilient.”
A better model?
The IOTC’s shock shift in stance on the health of tuna populations came after changes to technical measures, called the longline catch per unit effort (CPUE) indices. These indicators, little understood beyond a small group of specialist scientists, are fed into a model that is crucial in determining assessment outcomes.
The report detailing the new findings says the 2024 model represents a “marked improvement” over the previous model from 2021. It also says the changes build on recommendations from an independent review carried out in 2023.
What is catch per unit effort?
Catch per unit effort (CPUE) is a metric used in fisheries science to try to understand the abundance of a given fish in the sea. It is based on the amount of fish caught per a given unit of fishing effort. Fish can be measured by number or weight. The effort measurement depends on the fishing technique, eg fish caught per 1,000 hooks per day, or per hour of trawling.
The new model suggests the tuna was “in an overfished state from 2007 to 2019” but that the mass of adult fish (fisheries scientists look at “spawning stock biomass”) increased “considerably” after 2021.
But six independent scientists contacted by Dialogue Earth say they fear the changes make it appear that yellowfin stocks in the Indian Ocean are far healthier than the reality. All raised serious concerns over the new stock assessment.
“It’s wrong by all textbooks,” says Rainer Froese of the Helmholtz Centre for Ocean Research (Geomar).
Daniel Pauly, a professor at the University of British Columbia’s Institute for the Oceans and Fisheries, says he is “deeply suspicious of assessments saying that all is well with yellowfin tuna in the Indian Ocean, especially as we published a paper two years ago stating the opposite”.
Several scientists cited significant issues with the new IOTC methodology used to carry out the assessment. For example, the use of data from the Arabian Sea, which they say is patchy and unreliable, and therefore likely warps the overall assessment. They also take issue with the use of cluster analysis, which is a method of tracking stocks based on clusters of fish. Critics say it should not be used in this case, because the fishing methods for bigeye and yellowfin in tropical areas like the Indian Ocean are similar, making it difficult to distinguish between clusters.
The data analysis was “not well thought out”, says a source who has seen the code that was used. The source asked to remain anonymous to protect their ongoing work.
Furthermore, the team submitted the analyses just a day before the Cape Town meeting, leaving little time for scrutiny. The deadline is usually set at more than a week before meetings.
“[The attendees] weren’t told and didn’t have time to check,” adds the source. “Normally, you would have to explain why there is such a big difference in the findings, too. The [scientific committee] didn’t even do that. The chair from Spain [Gorka Merino] pushed things along.”
Merino, deputy chair of the IOTC’s scientific committee, says the 2024 yellowfin stock assessment was conducted in a “collaborative and transparent way” and informed by review by an international panel. He also stresses that a key index of tuna abundance was developed by scientists from Asian fleets, without any participation by European Union scientists, which undermines claims of European influence. (Critics say Asian fleets, like the European Union, have an interest in opposing limitations on their fishing.)
“It is a model that is more stable and robust than previous ones,” adds Merino.
Lobbying for tuna
Civil society organisations have repeatedly raised concerns about the growing influence of the industry on the IOTC. The number of lobbyists in the European Union delegation to IOTC meetings has more than doubled in recent years, from an average of eight between 2002 and 2015, to 18 between 2016 and 2022. Lobbyists now outnumber public officials and scientists, according to Bloom. The NGO adds that, of the 2,278 delegates from 30 nations who attended annual IOTC meetings between 2002 and 2022, one in five represented the European Union.
Meanwhile, the 68-boat European Union fleet (64 of which were from Spain and France) is the largest group in the Indian Ocean, according to the IOTC’s latest list of active vessels.
“There are too many vested interests involved in the IOTC,” says Nick Wise, founder of OceanMind, a nonprofit that focuses on enforcing oceans regulations.
Dialogue Earth sent a freedom of information request to the European Commission requesting details of attendees of fishing agreement negotiations between the European Union and Madagascar (one of the Indian Ocean’s coastal states), including for yellowfin tuna. Only redacted information that does not identify lobbyists was received.
Callum Roberts, a professor of marine conservation at the University of Exeter, tells Dialogue Earth he is “highly doubtful” the Indian Ocean’s yellowfin tuna population has grown.
“I think we all deserve far more robust evidence of tuna stock recovery before any credibility can be given to this convenient result,” he says.
Dialogue Earth spoke to Isabella Lövin, a Swedish member of the European parliament representing the Miljöpartiet (Green Party) and a member of the European Parliament’s Committee on Fisheries. She says the yellowfin assessments must be scrutinised by independent experts: “These shifting baselines have to be looked at.”
The Global Tuna Alliance, a group of retailers and supply chain companies, issued a statement saying: “engaging constructively with the IOTC and its partners to ensure the management of yellowfin tuna remains firmly grounded in science and precaution.”
Kitakado tells Dialogue Earth that, as the chair of the scientific committee, he cannot comment on “individual views or specific technical matters, which are either already addressed in the committee’s reports or are expected to be considered in upcoming discussions within the relevant working parties and the committee itself”.
He adds: “I appreciate the interest in this issue and trust that the committee will continue to fulfil its role with the seriousness and diligence it requires.”
The IOTC secretariat says it has no comment to make beyond the committee’s existing report.
A spokesperson for the European Commission’s Directorate-General for Maritime Affairs and Fisheries says the European Union “trusts” the 2024 IOTC stock assessment, adding it is “based on the rigorous work of highly qualified, independent scientists”.
On the presence of lobbyists in the European Union delegation, the spokesperson says: “The EU follows a wide and transparent consultation process with all stakeholders.”
Anne-France Mattlet is the director of Europêche, an industry body representing 45,000 fishing vessels, including the majority of the European Union vessels in the Indian Ocean. She says the IOTC stock assessments are “rigorous”, and that Europêche continues “to advocate for science-based conservation and management measures”.
This reporting was supported by IJ4EU (Investigative Journalism for Europe).