Four tuna species show signs of recovery from overfishing

The IUCN has upgraded the conservation status of four of the most commercially important tuna species, but the news masks other worrying declines

Bluefin Tuna

Atlantic bluefin tuna in the Mediterranean Sea – a population which has shown promising signs of recovery. (Image © Gavin Newman / Greenpeace)

In September, the International Union for Conservation of Nature (IUCN) announced some surprisingly good news. Four of the seven most commercially fished tuna species that appear on its Red List of Threatened Species are showing signs of recovery from overfishing.

That led the IUCN to update in its annual red list the status of the Atlantic bluefin from “endangered” to “least concern”. The southern bluefin went from “critically endangered” to “endangered” while the yellowfin and albacore moved from “near threatened” to “least concern”.

“But that doesn’t mean that we should go out and eat more fish just because these species are doing better than they were 10 or 15 years ago,” says Beth Polidoro, the red list coordinator for the IUCN group that reassessed the tuna species.

What it does mean is that efforts to manage tuna fisheries more sustainably appear to be working, particularly in the Asia-Pacific region, where most tuna is fished.

“We should learn from what we’re doing right and do it in more parts of the world across all stocks and species,” says Polidoro, an associate professor of environmental chemistry and aquatic conservation at Arizona State University in the United States. She notes that tuna species such as the Pacific bluefin remain severely depleted, with the current population equalling less than 5% of the biomass it contained before commercial fishing began.

Experts caution that the IUCN reassessment must be understood in context and not used to press for higher catch quotas for particular stocks of tuna, a long-lived and highly migratory top predator.

Assessing tuna’s extinction risk

The IUCN red list evaluates the risk of extinction for the global population of a species.

Scientists reviewed tuna stock assessments from regional fisheries, data from scientists and independent organisations, as well as peer-reviewed studies, to estimate changes in population over three tuna generations.

Such global surveys, however, can mask declines in regional populations of tuna species that are commercially fished, according to Polidoro and Grantly Galland, a senior officer with the Pew Charitable Trusts international fisheries programme who focuses on tuna.

For instance, they say, the IUCN reassessment found improvements in the population of yellowfin tuna, prompting the change in its status from near threatened to least concern. “That’s for the global species, but the population of yellowfin in the Indian Ocean is very poorly managed, and is approaching the point of potential collapse there,” says Galland.

Polidoro notes the same is true for Atlantic bluefin, whose status moved from endangered to least concern.

“That’s driven primarily by the increase in the population that’s found in the Mediterranean Sea, which is actually 80%, more or less, of the global population,” she says.

Fishing in the Indian Ocean
A French purse seiner vessel loads skipjack and yellowfin tuna attracted by a fish aggregation device in the Indian Ocean. Grantly Galland of Pew Charitable Trusts says the population of yellowfin tuna in the region is reaching the point of potential collapse. (Image © Jiri Rezac / Greenpeace)

However, Polidoro notes, the Gulf of Mexico’s population of Atlantic bluefin “is doing quite poorly. It has never really recovered from overfishing in the 1960s and 70s.”

The IUCN reassessment also upgraded Pacific bluefin from vulnerable to near threatened.

“That’s not because it’s doing better per se, but because there’s now better data that showed the status of the population,” says Polidoro. “So it’s limping along at a very, very low population size compared to historical levels.”

Where tuna are doing better

The Western and Central Pacific Fisheries Commission (WCPFC) regulates the region’s US$5 billion fishery, setting catch quotas for albacore, bigeye, Pacific bluefin, skipjack and yellowfin tuna. China operates the largest tuna fleet in the region, according to commission records.

Observers do not expect the IUCN reassessment to result in a change in catch limits set by the WCPFC and other RFMOs.

What is an RFMO?


Regional fisheries management organisations regulate fishing activities in regions of the high seas. Most of these international bodies have powers to set catch and fishing limits and govern either highly migratory species such as tuna, or mixed fish populations in a specific area.

“They all have their own science, their own scientists and they don’t make substantial changes in their operations based on species being down-listed or up-listed, as they manage at the population level not the species level,” says Galland.

WCPFC science manager SungKwon Soh said in an email that he could not comment on the IUCN reassessment of tuna species but noted that commission members “take their own initiative to conduct quota allocation and management practices”.

Galland, who closely follows the WCPFC and other RFMOs, attributes the apparent recovery of some tuna species to polices the regional fisheries bodies have implemented over the past decade to more sustainably manage commercial fish stocks.

Fishermen Catch Tuna
Fishers in the Maldives catch skipjack tuna in the Indian Ocean. The pole-and-line method is considered one of the most sustainable ways to catch tuna. (Image © Paul Hilton / Greenpeace)

“Fortunately, in the case of tunas, they are generally pretty well managed, and generally in pretty good status,” he says of the WCPFC.

Even so, pressure is building for the WCPFC to take more aggressive action to ensure the long-term sustainability of tuna stocks.

The Marine Stewardship Council (MSC) certifies the sustainability of tuna caught by WCPFC fisheries and others around the world. It is a crucial label of approval, given that the commission oversees half the world’s commercial tuna catch. Of all MSC-certified tuna, 73% is from the central and western Pacific.

In July, the MSC issued a statement warning that the commission’s tuna fisheries risked losing their certification unless the WCPFC made substantial progress in adopting “harvest strategies” – a set of rules and objectives designed to ensure the sustainability of tuna stocks by altering catch limits as conditions change.

“The stocks are in healthy shape, and that’s why it’s important to put in these harvest strategies now when tuna species are not up against the wall and it hasn’t become a crisis,” says Bill Holden, a senior MSC tuna fisheries outreach manager based in Sydney, Australia.

Soh said he expects the commission to take up the MSC’s concerns at its virtual meeting in December.

The impact of the pandemic and climate change

The absence of in-person meetings during the Covid-19 pandemic has slowed progress on adopting harvest strategies, according to Holden.

The pandemic has also upended monitoring of tuna fishing as, in April 2020, the WCPFC suspended requirements that fishery observers be onboard vessels to deter illegal, unreported and unregulated fishing. In August this year, the commission extended the suspension until 15 December, but noted that vessel operators may choose to place observers onboard at their discretion if they follow safety protocols.

Holden says observers are a key source of real-time data on fisheries, and the decline in coverage during the pandemic – some Pacific island nations’ borders remain closed – will impact the completeness of stock assessments in the coming years.

“Observers are very good at collecting data and we know that the data is very reliable,” he says.

The sustainability of fisheries depends on collecting such data to assess changes in population and reproductive rates of fish stocks. That’s always difficult when it comes to tuna, given that the fish migrate over vast distances. But climate change will make the task even more complicated, according to Polidoro.

“It’s really going to mess up fisheries,” she says, noting that rising ocean temperatures could alter tuna reproduction and migration patterns.

“It is a challenge to estimate population sizes for things that you can’t necessarily count individual by individual,” she adds. “And so keeping track of where the tuna are and what population they belong to is going to become increasingly challenging over the next couple of decades.”

Additional research by Regina Lam.