World Tuna Day, observed on May 2^nd, was established in 2016 by the United Nations General Assembly to draw attention to the importance of sustainable fishing and conservation management.

With the start of the UN Decade of Ocean Science for Sustainable Development (2021-2030) and Ecosystem Restoration (2021-2030), it’s a good time to take stock of the state of tuna in our ocean and what the future may hold for this iconic fish.

In March, Seaspiracy brought awareness of the destructive impact of large-scale industrial fishing on the world’s most important ecosystems and the consequences for the species in our seas. While outdated in many of its facts, the controversial Netflix documentary shocked the public by revealing several harrowing discoveries and uncovering important questions surrounding the future of commercial fishing for tuna.

There are 15 known species of tuna, five of which are the most sourced by commercial fisheries: The Bluefin, Yellowfin, Bigeye, Albacore, and Skipjack. In the 1960s, the demand for tuna grew, and industrial tuna fisheries reached their peak. A combination of ineffective management techniques and consistently high demand has led to the fatal decline of tuna, specifically Bluefin Tuna, Skipjack Tuna, and Yellowfin.

In 2016, The International Scientific Committee for Tuna (ISC) estimated that under 3 percent of the original, pre-fished bluefin tuna population remains in our waters. Considering the average lifespan of tuna is around 40 years, this is worryingly low. At the time, experts were predicting bluefin to have less than a 1 percent chance of recovering to healthy levels within the next two decades¹. Two years later, the UN Food and Agriculture Organization reported that catches of tuna were still increasing despite the concerning numbers, reaching their highest levels of 7.9 million metric tons in 2018 –approximately the weight of around 75,000 blue whales. According to the United Nations, recent data shows that 33.3 percent of tuna stocks are still estimated to be fished at unsustainable levels.

Due to the decreasing populations, tuna has become the most expensive commercial fish species out there, accounting for an annual sale value of US$40 billion in 2016². Tuna fisheries are present in over 96 countries, with an annual value of almost 10 billion USD - many of these fisheries are experiencing declining catch rates and increasing pressure to adopt better conservation management approaches. Skipjack tuna is in the best status compared to the larger tuna species that take years to mature³. Juvenile Yellowfin and Bigeye are often caught while targeting Skipjack tuna, removing an abundance of juvenile tuna that have not yet spawned.

A World Without Tuna

Compared to other tuna, the status of the bluefin in the Western Atlantic and the Mediterranean is the most severe⁴. Tuna are apex predators, meaning they are at the top of the food chain, keeping prey species in check and providing ecological stability. The removal of bluefin from the food chain begins a domino effect down the trophic levels. Species that are normally controlled by the presence of tuna will begin to thrive and grow. This can have unpredictable effects on the interactions with the ecosystem.

Scientists have observed many times the negative impacts of removing a predator. When sea otters declined along the Pacific coast of North America, sea urchin populations rose sharply and led to the destruction of the kelp beds. Without the presence of the sea otters, nothing was controlling the growth of sea urchins⁵. Without bluefin tuna, a possible scenario could include small fish population, like sardines, increasing along with crustaceans and cephalopods, a common source of food for tuna⁶.

In this scenario, the fishing industry may look for alternative sources, perhaps targeting the rising smaller fish species. But will it be enough to replace the economic benefits tuna bring?

The Asia pacific tuna industry employs around six million people and is an important source of income for many developed and developing countries⁷. This fishing industry supplies 60 percent of canned tuna globally, mainly Skipjack, providing an inexpensive protein source. On the other hand, auctions receive a large profit from restaurateurs who seek and bid for large fish. Of the total global fish trade, tuna species contribute 30 percent annually⁸. One of the largest tuna producers is Indonesia, with an exporting value of $760 million⁹. A majority of their catch is caught by purse seine; however, many fisheries employ hundreds of local fishers to catch by pole and line. With tuna on the decline, alternative small fish species may not be enough to sustain the economy and provide an efficient food source able to keep up with the growing populations and demand.

An Alternative Future

Around the globe, organizations are trying to promote conservation management of fish stocks and reduce bycatch. Early signs show that these efforts are paying off. The Marine Stewardship Council (MSC) has introduced more attractive incentives for certified fishing vessels¹⁰. In the United States, the National Oceanic and Atmospheric Administration (NOAA) has required permits, electronic monitoring systems to prevent/minimize bycatch, and applied size and quantity limits. There have also been restrictions added in the spawning season to avoid the capture of juvenile tuna¹¹.

According to MSC, there have been improvements in the global stocks of tuna. In January 2020, the Global Environmental Facility (GEF) and Food and Agricultural Organisation (DEF-FAO) reported that 8 of the 13 major tuna stocks are no longer experiencing overfishing as a result of a five-year, $50-million program to protect biodiversity in international waters. The GEF-FOA program is seeing promising results after committing to raise awareness on ocean issues to strengthen government decision-making and reduce bycatch and marine pollution with changes to fishing gears¹². More recently, the Japanese government has introduced new legislation to stop illegal, unreported, and unregulated seafood from being distributed¹³.

Positive stories of sustainability and economic performance are also emerging from the Western and Central Pacific region, where over 30 percent of world tuna catches are sourced. In April 2021, Cefas and the University of Exeter observed that Atlantic bluefin tuna have returned to UK waters, following a long absence linked to population decline.

Research has directed efforts into finding ways of providing more accurate estimations and predictions of fish numbers to support fisheries management. A recent study in Scientific Reports sought to improve techniques using environmental DNA, or eDNA. The method involves measuring the cellular material that is shed from organisms and release into the surrounding environment (eDNA), and was originally used to estimate the abundance of eels within breeding waters. Today, it is often used as early identification for invasive species. Using unique molecular identifying tags, scientists successfully identified 94 percent of haplotypes (a group of genes within an organism that was inherited together from a parent) from Pacific bluefin tuna eDNA¹⁴. In a 2020 study published in Scientific Reports, scientists investigated the relationship between fishery performance (catch data) in the Federated States of Micronesia and environmental data to evaluate the potential predictability of catches. The environmental data represents El Nino-like variability and could therefore help predict catches of Skipjack tuna¹⁵.

Many environmental and government bodies have a goal to improve tuna populations and sustainable fishing. Progress towards a more productive and sustainable ocean can be seen as a result of drastic changes adopted by some tuna fisheries. Of course, more needs to be done. The socio-economic importance of the tuna industry requires urgent effective conversation management approaches, improvements in fish population estimates, attention to long-term goals, and close collaboration between all ocean stakeholders (from governments to fishers). As it stands today, the future of the tuna industry is largely unpredictable. Still, there are reasons to be optimistic for the future of tuna.

By Elise Poore, ECO Contributor

Read more about this topic here:

1. https://www.pewtrusts.org/en/research-and-analysis/articles/2016/04/25/new-science-puts-decline-of-pacific-bluefin-at-974-percent
2. Macfadyen, G., Huntington, T., Defaux, V., Rogers, A., Galland, G., & Nickson, A. (2016). Netting Billions: A Global Valuation of Tuna. Retrieved from: https://www.pewtrusts.org/en/research-and-analysis/reports/2016/05/netting-billions-a-global-valuation-of-tuna
3. https://www.worldwildlife.org/species/skipjack-tuna
4. https://www.nationalgeographic.com/animals/fish/facts/atlantic-bluefin-tuna
5. Bodkin, J. L. (2015). Historic and contemporary status of sea otters in the North Pacific. In Sea otter conservation (pp. 43-61). Academic Press.
6. WWF On the Brink to Tuna Collapse. https://wwfeu.awsassets.panda.org/downloads/onthebrinktunacollapse.pdf
7. Asian Development Bank (ADB). 2013. Sustainable tuna fisheries in Asia and the Pacific. Available at: www.adb.org/features/sustainable-tuna-fisheries-asia-and-pacific-numbers
8. https://www.pewtrusts.org/en/projects/archived-projects/global-tuna-conservation
9. Duggan, D. 2017. Simple Economics in Small Scale Tuna Fisheries: Results of an economic-survey conducted in four MDPI sites in Eastern Indonesia http://mdpi.or.id/images/pdf_list/publications_reports/Economic_Report_MDPI.pdf
10. MSC Annual Report 2019-2020. Retrieved from: https://www.msc.org/docs/default-source/default-document-library/about-the-msc/msc-annual-report-2019-2020.pdf
11. https://www.fisheries.noaa.gov/feature-story/new-requirements-protect-bluefin-tuna-expand-opportunities-other-fisheries
12. http://www.fao.org/news/story/en/item/1258859/icode/
13. https://www.globaltunaalliance.com/general/global-seafood-coalition-applauds-japanese-government-on-actions-to-eliminate-iuu-fishing-calls-for-further-collaboration-between-industry-and-governments/
14. Yoshitake, K. et al (2021). Estimation of tuna population by the improved analytical pipeline of unique molecular identifier-assisted HaCeD-Seq (haplotype count from eDNA). Scientific Reports, 11(1), 1-12.
15. Kim, J., Na, H., Park, Y. G., & Kim, Y. H. (2020). Potential predictability of skipjack tuna (Katsuwonus pelamis) catches in the Western Central Pacific. Scientific reports, 10(1), 1-8.