Marcel Kroese is WWF’s global tuna lead and has been involved in marine conservation as a researcher and professional since 1992, with working experience in East and West Africa, the Pacific, and Central America.
Picture a tuna. No, not a can. A fish. It is sleek and strong. Its scales flash as it dives like a torpedo to depths of 1,000 meters. If it were a car, James Bond would drive it. If it were a cat, it would be a cheetah. Yet these spectacular, athletic sea creatures are not afforded the same awe and wonder by humans as the big cats. We value tuna as a luxury food or a more humble “shelf-stable protein,” which is handy when stocking up for a pandemic. Either way, they are just food.
Certainly, tuna have fed countless generations throughout human history. From the palm-fringed islands of the Pacific to the diverse nations of the Mediterranean, tuna have been part of the diet and part of the culture. But before they make it to the plate, they played a vital role in the functioning of the ocean ecosystem – because fish don’t just inhabit the ocean. They fuel it.
Big fish like mature tunas perform “ecological maintenance” – storing and cycling nutrients and carbon. In fact, the whole ocean web of life, from the mighty tunas to the microscopic plankton, play a role in the ocean’s ability to absorb humanity’s CO2 emissions. Just by swimming, diving, eating and excreting, tunas are mixing water layers and moving nutrients that fuel the whole ocean food chain.
So, tuna are important to both people and the planet that supports us, which means accurately assessing the health of tuna stocks should be a priority. But, at present, there is a range of disparate views – from those who see plenty of fish in the sea, and those who see us caught in dangerous currents.
First, it’s important to note there are different tuna species in different parts of the ocean that are categorized as different populations to a biologist or different “stocks” if the intent is harvesting. How many of these stocks are healthy? Estimates range up to 87 percent, according to an International Seafood Sustainability Foundation (ISSF) report. That sounds good – but it is skewed by one particularly large stock. And what do we mean by “healthy” when it comes to a population of fish?
The United Nations’ Food and Agriculture Organization provides guidance on healthy stocks through an assessment of overexploited, fully exploited and non-fully exploited. Fully exploited is defined as current stock at 40 to 60 percent of the unfished level, and a spawning (mature) stock biomass between 20 to 40 percent of unfished levels. By comparison, overexploited is when the stock is below 40 percent of unfished levels and spawning stock biomass falls below 20 percent. FAO provides additional guidance, but fishing mortality and spawning stock are the most prevalent and available indicators in scientific literature.
Examining the status of 23 tuna stocks most often caught (bluefin tuna were excluded because their stock levels are too low to be considered for commercial fisheries), one of the key indicators – the spawning biomass – could not be determined for three of the tuna stocks because of the lack of data. In six cases, it was possible to assess the current spawning biomass, but impossible to determine how it compared to the unfished biomass – so, of limited use. Where data is available, nearly half of the stocks were below the 40 percent original spawner biomass level, and approximately 30 percent of stocks were at or below 20 percent – the FAO limit of overfishing.
It’s easy to get lost in the sea of numbers, but The State of the World Fisheries and Aquaculture reports that 66.6 percent of the world’s tuna fisheries are considered within biological limits and 33.3 percent are fished at biological unsustainable levels.
This “two-thirds within biological limits” might seem like a passing grade. But is it the whole picture? The fact that one of the fundamental metrics is not available for almost a quarter of stocks tell us clearly it is not. Other metrics can be used as proxy indicators of the health of stocks, but the state of the spawning biomass in considered fundamental.
WWF’s tuna strategy calls for the stock spawning biomass to stay at 40 percent or higher – the upper level of FAO’s fully exploited category. We believe this higher threshold for the spawning biomass is needed as a buffer against the uncertainty of the impact of climate change. It is hard to argue against having more mature spawning fish in any population, and with the uncertainty of climate and the poor quality of some fisheries data, more spawners are certainly better than fewer spawners.
Much of WWF’s effort to advance our tuna strategy takes place at the regional bodies that are responsible for tuna management. We aim to improve management measures to rebuild stocks, reduce juvenile mortality and reduce the use of detrimental fishing gear that kills or injures endangered, threatened, and protected species, such as dolphins, turtles, sharks, and seabirds. Our partner engagement is aimed at guiding retailers to source fish from healthy tuna stock, where the spawning biomass is as close to 40 percent as possible. Our engagement with coastal states recognizes the importance of healthy tuna populations to local livelihoods and food security.
Regional fishery management organizations have a variety of management interventions to keep tuna at specific target levels, including adopting harvest control rules and country-based catch limits. The stocks in good health – the ones propping up that 87 percent healthy tuna stocks figure – are mostly in the western and central Pacific, where the stocks are so vast, they provide about 60 percent of all the tuna consumed. But it’s not just prolific fish; the coastal states in this region adopted a central management authority for their waters and were very conservative about exploiting the stocks to low levels.
They were successful because most of the tuna occur inside their exclusive economic waters for most of their lives. Across the rest of the ocean, tuna spend most of their time outside counties’ territorial waters – in the high seas. It is in the high seas, where all nations have the freedom to fish under rules set by regional fisheries management organizations. These bodies are plagued by a focus on the short-term, slow decision-making and weak enforcement, and tuna stocks have suffered as a result.
WWF has several key recommendations for the Indian Ocean Tuna Commission, with particular focus on yellowfin tuna – a stock on the verge of collapse that plays a significant role in the food security, income generation, and economic development of marginalized communities of the Indian Ocean coastal states. WWF calls for capping the catch in the range of 340,000 to 350,000 tons, achieved through an overall catch reduction of 15 to 20 percent from 2015 levels to rebuild the Indian Ocean yellowfin tuna over a period of 10 years, in order to have a 50 percent probability of stock rebuilding by 2027. We further call for a new approach to managing fish aggregating devices, which are largely responsible for juvenile mortality – catching yellowfin before they have had a chance to reproduce.
As important as it is to undertake informed, science-based sustainable tuna management strategies, a healthy ocean is an even more important goal. It is therefore deeply concerning that fisheries, primarily tuna fisheries, are responsible for decimating oceanic sharks and ray populations – caught incidentally or on purpose as part of tuna fishing operations.
The health of apex predators and ocean megafauna is extremely important to the health of the ocean. As described earlier, these animals shape their environment as much as it shapes them. Research has shown coral reefs with healthy shark populations are healthier and more resilient than those without. A severe imbalance in ecosystems, such as the dramatic reduction in apex predators, is bad for the ocean and therefore bad for people.
The world needs ocean-friendly fisheries, particularly for tuna. To reach this goal, we need better data, better enforcement and deeper commitments from governments and industry to make sustainability the hallmark of tuna fisheries. While current data may be incomplete, we know enough to know we have to do better, and we don’t have much time to get it right.
Photo courtesy of WWF