Controversy over the state of bluefin tuna in the Indian Ocean

The Indian Ocean Tuna Commission's scientific committee made headlines in early December 2023 with a surprising announcement: the yellowfin tuna population in the region, once considered overfished or at risk of overfishing, was now in a healthier state. However, this shift from red to green has been met with skepticism by outside experts and conservationists.

Professor Daniel Pauly of the University of British Columbia's Institute for the Oceans and Fisheries is among those expressing doubts. He is "deeply suspicious" of the new assessment, questioning whether it accurately reflects the current state of the yellowfin tuna population in the Indian Ocean. Rainer Froese of the Helmholtz Centre for Ocean Research (Geomar) shares similar sentiments, stating that the changes make it appear that the stocks are far healthier than the reality, which he describes as "wrong by all textbooks."

The concern stems from several factors. For instance, between 2018 and 2022, an average of 429,421 tonnes of yellowfin were caught each year, significantly exceeding the maximum sustainable yield (MSY) of 349,000 tonnes recommended by the committee. The data analysis, which was submitted just a day before the scientists' data preparation meeting, has also been criticised for being "not well thought out."

Critics 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. In the Indian Ocean, where the fishing methods for bigeye and yellowfin in tropical areas are similar, this method may not provide an accurate representation of the yellowfin tuna population.

Moreover, the use of data from the Arabian Sea, which is considered patchy and unreliable, likely warps the overall assessment. The mass of adult yellowfin tuna (fisheries scientists look at "spawning stock biomass") increased "considerably" after 2021, but this may not necessarily indicate a healthier population.

Six independent scientists have expressed concerns over the new yellowfin tuna stock assessment. In 2015, the scientific committee of the Indian Ocean Tuna Commission had declared yellowfin tuna "overfished" with 94% certainty. Yet, the new model suggests that yellowfin tuna was "in an overfished state from 2007 to 2019."

The consequences of an inaccurate assessment could be severe. If the assessment is wrong, the lives of millions of people who rely on fisheries for their livelihoods could be drastically affected, and the long-term health of the ocean could be damaged. Conservationists warn that a collapse in the yellowfin population could have serious repercussions for Indian Ocean ecosystems.

Despite these concerns, the committee's latest findings were presented as part of a comprehensive collaboration aimed at ensuring long-term sustainability, reducing post-harvest losses, and improving profitability. The decision to change the status of yellowfin tuna allows international fleets to catch more of the valuable fish. The market for yellowfin tuna is worth billions of dollars annually, making it a significant player in the global fishing industry.

As the debate continues, it is crucial to ensure that scientific rigour and transparency are maintained in the assessment process. The Indian Ocean, which is bordered by Africa, Asia, and Australia, is the world's second-largest tuna-producing region, accounting for over a fifth of the world's supply and worth USD 2.3 billion annually. The health of its yellowfin tuna population is of global importance.