In practical terms, the decision was the first step in allowing international fleets to catch more of the valuable fish.<\/p>\n\n\n\n
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. <\/p>\n\n\n\n
\u201cI thought that it must be some kind of miracle,\u201d says Iris Ziegler, head of fisheries policies and ocean advocacy at the German Foundation for Marine Conservation (DSM<\/a>), who attended the Cape Town meeting. \u201cIt really did not make sense.\u201d<\/p>\n\n\n\n In 2015, the scientific committee of the Indian Ocean Tuna Commission (IOTC) had declared<\/a> yellowfin tuna (Thunnus albacares<\/em>) \u201coverfished\u201d, with 94% certainty. It 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.<\/p>\n\n\n\n The term \u201coverfished\u201d means the total biomass of a fish is below a determined limit. The term \u201coverfishing\u201d indicates the current level of fishing may result in a species becoming overfished, if it is not already.<\/p>\n\n\n\n Between 2018 and 2022, an average 429,421 tonnes of yellowfin were caught each year according to a 2023 IOTC scientific committee report<\/a>, 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.<\/p>\n\n\n\n MSY is a common metric<\/a> in fisheries, used to estimate the largest amount of fish that can be sustainability caught over time. Catch limits<\/a> 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.<\/p>\n\n\n\n Despite this apparent sustained overfishing, by 2024 IOTC scientists were saying this species was in a healthy state.<\/p>\n\n\n\n So, did yellowfin stocks suddenly become markedly healthier? Were the decade\u2019s preceding estimates wrong? Or was the new assessment far from the reality of what was in the ocean?<\/p>\n\n\n\n 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<\/a> it is an example of the European Union\u2019s 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 \u2013 fishers who depend on tuna for food and income.<\/p>\n\n\n\n \u201cIt\u2019s all about profit,\u201d says John Burton, founder of the UK-based sustainable fishing nonprofit SFACT<\/a>. \u201cStocks 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.\u201d<\/p>\n\n\n\n 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.<\/p>\n\n\n\n The Indian Ocean, which is bordered by Africa, Asia and Australia, is the world\u2019s 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\u2019s supply and is worth USD 2.3 billion, according to a 2023 study<\/a>.<\/p>\n\n\n\n Yellowfin \u2013 a torpedo-shaped predator named for its bright yellow dorsal fin \u2013 accounts for a significant amount of the region\u2019s tuna catch. Most is caught by industrial ships using purse seine<\/a> and baited hook longline<\/a> methods, for the canned tuna and sashimi markets.<\/p>\n\n\n\n Yellowfin biomass declined globally by 54%<\/a> between the 1950s and 2020, according to a global study in 2023. The greatest decline over that period \u2013 70% \u2013 was in the Indian Ocean, where the researchers concluded the species is in \u201cdire straits\u201d. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species rates<\/a> yellowfin tuna globally as not particularly threatened. However, scientists who assessed the Indian Ocean population using the same IUCN methodology concluded it was \u201cvulnerable\u201d<\/a>.<\/p>\n\n\n\n Conservationists warn a collapse in the yellowfin population could have serious repercussions for Indian Ocean ecosystems, where tuna play<\/a> a key role as a top predator. It would also be devastating<\/a> for the tens of millions of people in coastal areas who rely on fisheries for their livelihoods.<\/p>\n\n\n\n \u201cIf unsustainable yellowfin fishing continues, it could have permanent and extremely damaging effects on millions of people and the planet,\u201d says Umair Shahid<\/a>, the World Wide Fund for Nature\u2019s (WWF) Indian Ocean tuna manager.<\/p>\n\n\n\n Shahid urges caution over the 2024 assessment: \u201cWhile 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.\u201d<\/p>\n\n\n\n The IOTC\u2019s shock shift in stance on the health of tuna populations came after changes to technical measures, called the longline catch per unit effort<\/a> (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.<\/p>\n\n\n\n The report detailing the new findings says the 2024 model represents a \u201cmarked improvement\u201d over the previous model from 2021. It also says the changes build on recommendations from an independent review carried out in 2023.<\/p>\n\n\n\n What is catch per unit effort?<\/p> Catch per unit effort (CPUE) is a metric<\/a> 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.<\/p><\/div><\/div>\n\n\n\n The new model suggests the tuna was \u201cin an overfished state from 2007 to 2019\u201d but that the mass of adult fish (fisheries scientists look at \u201cspawning stock biomass\u201d) increased \u201cconsiderably\u201d after 2021.<\/p>\n\n\n\n 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.<\/p>\n\n\n\n \u201cIt\u2019s wrong by all textbooks,\u201d says Rainer Froese of the Helmholtz Centre for Ocean Research (Geomar<\/a>).<\/p>\n\n\n\n Daniel Pauly, a professor at the University of British Columbia\u2019s Institute for the Oceans and Fisheries, says he is \u201cdeeply suspicious of assessments saying that all is well with yellowfin tuna in the Indian Ocean, especially as we published a paper<\/a> two years ago stating the opposite\u201d.<\/p>\n\n\n\n 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, an approach for identifying fishing methods based on the particular mixture of species present in a catch (a cluster). 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. This makes it is difficult to distinguish between the two tuna species, which can potentially inflate yellowfin numbers.<\/p>\n\n\n\n The data analysis was \u201cnot well thought out\u201d, says a source who asked to remain anonymous to protect their ongoing work.<\/p>\n\n\n\n Furthermore, the team submitted the analyses just a day before the scientists\u2019 data preparation meeting, leaving little time for scrutiny. The deadline is usually set at more than a week before meetings.<\/p>\n\n\n\n \u201c[The attendees] weren\u2019t told and didn\u2019t have time to check,\u201d adds the source. \u201cNormally, you would have to explain why there is such a big difference in the findings, too. The [scientific committee] didn\u2019t even do that.\u201d<\/p>\n\n\n\n Merino, deputy chair of the IOTC\u2019s scientific committee, says the 2024 yellowfin stock assessment was conducted in a \u201ccollaborative and transparent way\u201d, and informed by a review undertaken 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’s, have an interest in opposing limitations on their fishing.)<\/p>\n\n\n\n \u201cIt is a model that is more stable and robust than previous ones,\u201d adds Merino.<\/p>\n\n\n\n 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<\/a> represented the European Union.<\/p>\n\n\n\n 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<\/a> the IOTC\u2019s latest list of active vessels.<\/p>\n\n\n\n \u201cThere are too many vested interests involved in the IOTC,\u201d says Nick Wise, founder of OceanMind<\/a>, a nonprofit that focuses on enforcing oceans regulations.<\/p>\n\n\n\n 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\u2019s coastal states), including for yellowfin tuna. Only redacted information that does not identify lobbyists was received.<\/p>\n\n\n\n Callum Roberts, a professor of marine conservation at the University of Exeter, tells Dialogue Earth he is \u201chighly doubtful\u201d the Indian Ocean\u2019s yellowfin tuna population has grown.<\/p>\n\n\n\n \u201cI think we all deserve far more robust evidence of tuna stock recovery before any credibility can be given to this convenient result,\u201d he says.<\/p>\n\n\n\n Dialogue Earth spoke to Isabella L\u00f6vin, a Swedish member of the European parliament representing the Milj\u00f6partiet<\/em> (Green Party) and a member of the European Parliament\u2019s Committee on Fisheries. She says the yellowfin assessments must be scrutinised by independent experts: \u201cThese shifting baselines have to be looked at.\u201d<\/p>\n\n\n\nFrom red to green<\/h2>\n\n\n\n
Stocks have been deep in the red for years, then suddenly they turn green<\/blockquote>John Burton, founder, SFACT<\/cite><\/div><\/div>\n\n\n\n
An ocean of tuna?<\/h2>\n\n\n\n
![\"Jumping](\"https:\/\/dialogue.earth\/content\/uploads\/2025\/07\/Jumping-Yellowfin-Tuna-Maldives_Alamy_CY13AY.jpg\")
<\/div>A better model?<\/h2>\n\n\n\n
Lobbying for tuna<\/h2>\n\n\n\n