The recovery of Pacific bluefin tuna has achieved a major milestone—the species exceeded international targets a decade ahead of schedule.

The rebuilding of Pacific bluefin tuna reflects a fisheries management success. International organisations cooperated across the Pacific to reverse decades of overfishing for the prized species.

The International Scientific Committee for Tuna and Tuna-Like Species in the North Pacific Ocean (ISC), including NOAA Fisheries researchers, provided scientific expertise to inform conservation measures. The Inter-American Tropical Tuna Commission (IATTC) and Western and Central Pacific Fisheries Commission (WCPFC) adopted these measures.

The ISC recently finalised the new stock assessment at the annual meeting in Victoria, Canada. The assessment confirmed that the stock reached the second rebuilding target in 2021. If the current management measures persist, the population growth is expected to continue growing.  

“This is an amazingly resilient fish and the new assessment is showing us that. While the population is thriving, ongoing monitoring of data quality is essential to ensure the continued accuracy of the assessment,” said Dr Huihua Lee, a research mathematical statistician at NOAA Fisheries’ Southwest Fisheries Science Centre who led the work on the stock assessment in the United States. 

“It also demonstrates the success of coordinated scientific efforts taken by the member countries through the ISC.” 

Dr Lee said the stock assessments translate decades of high-quality data on Pacific bluefin and a thorough understanding of the biology of the species into accurate predictions of future trends.

Pacific bluefin tuna are the largest species of tuna in the Pacific with adults reaching nearly 10 feet in length and 990 pounds. The habitat of this Highly Migratory Species mostly spans the temperate waters of the North Pacific—from East Asia to the North American West Coast. They are also among the fastest swimming species on the planet and live an average of 15 years.

In the United States, recreational and commercial vessels primarily land Pacific bluefin tuna using hook and line or purse seines. In 2022, U.S commercial fishers harvested 368 metric tons of Pacific bluefin tuna, grossing more than US$2.2 million in on-the-dock revenue. 

The total U.S fishing effort, both recreational and commercial, represented around 10 percent of total Pacific bluefin tuna landings that year. Japanese and Mexican vessels harvest the majority of the annual catch.

When harvested on the West Coast, Pacific bluefin tuna have already traversed the Pacific from their spawning grounds between central Japan and the northern Philippines and in the Sea of Japan. They arrive off the coast of Baja California, Mexico, at around one-year-old. They stay in the open waters off the United States and Mexico, feeding on squid, sardines, saury, and herring, among other fish. Once 3 to 5 years old, they migrate back to their spawning grounds—a nearly 6,000-mile journey that takes as little as 55 days for the speedy fish.

While the successful management of bluefin requires significant international cooperation, it also demands coordination within NOAA Fisheries. The Southwest Fisheries Science Centre contributes scientific analyses to the ISC stock assessment. 

The West Coast region and the Pacific Islands Regional Office collaborate on stock management, both domestically and internationally.

“Close collaborations between managers and scientists have been really key for the United States to develop a cohesive strategy to rebuild this Pan-Pacific stock. Everyone has played an important role in the science and management process, and our cumulative efforts have resulted in a success story for Pacific bluefin,” said Valerie Post, a Fishery Policy Analyst with the NOAA Fisheries Pacific Islands Regional Office.

Bluefin are assessed based on their unfished spawning stock biomass—the theoretical amount of fish there would be in the absence of fishing. Overfishing in the late 1990s and 2000s reduced the estimated bluefin biomass to a historic low of 2 percent of its potential unfished level in 2009–2012. This alarming decline prompted multilateral action beginning in 2011 to stem overfishing and rebuild the bluefin stock. The goal was to rebuild to at least 20 percent of the spawning stock biomass by 2034.

Pacific bluefin tuna are considered one stock throughout their range. The IATTC manages them in the eastern Pacific Ocean and the WCPFC manages them in the western and central Pacific Ocean. Both base their bluefin tuna management and conservation measures, which have been adopted by consensus, on science produced by the seven-country ISC. The United States is a member of both commissions. NOAA Fisheries leads U.S delegations and implements the conservation and management measures agreed to by the organisations.

Management efforts to rebuild the stock started in 2011 when WCPFC members agreed to reduce their catch of both juvenile and larger bluefin. This gave more fish the opportunity to reach maturity and reproduce. The following year, the IATTC implemented conservation measures to reduce catch in its management area. These two commissions have continued to coordinate across the Pacific, using the best available science to inform management decisions across the entire range of the species. 

Even as their numbers began to grow, NOAA Fisheries received a petition in 2016 to list the Pacific bluefin as threatened or endangered under the Endangered Species Act. A status review team conducted a 12-month review. They determined that while the population was near historical lows, the roughly 1.6 million fish was sufficient to avoid the risk of extinction. Management changes effectively addressed concerns about overfishing.

Yet, the rebuilding happened much faster than expected. With each spawning female laying millions of eggs per batch, Pacific bluefin tuna possess the natural ability to rebound when coordinated international efforts reduce fishing pressure. The recent stock assessment shows that in 2022 the number of spawning bluefin reached 23.2 percent of the potential unfished spawning stock. This milestone marks the first time the population has surpassed the associated maximum sustainable yield level for the species. The rapid rebuilding of the Pacific bluefin stock suggests the possibility of increased harvests in future years as the population continues to grow.

“There is a point where you can find a balance between abundant harvest while also allowing the stock to grow in perpetuity, and we’ve now exceeded that point,” said Celia Barroso, a Fishery Policy Analyst at the NOAA Fisheries West Coast region.

The Joint IATTC-WCPFC Northern Committee Working Group on bluefin management is set to meet in Japan in July to recommend conservation and management measures for 2025 and beyond. The IATTC and WCPFC must then adopt the recommendations at their annual meetings later this year.

The next step in the international management of bluefin is the development of a long-term harvest strategy starting next year. Southwest Fisheries Science Centre researchers will help lead a Management Strategy Evaluation. It will incorporate engagement from the fishing industry, managers, scientists, and environmental groups to inform the new harvest strategy.

“The recovery of Pacific bluefin tuna shows what we can achieve when scientists, managers, and the fishing industry work together in the international arena in pursuit of a common objective,” said Ryan Wulff, Assistant Regional Administrator for the NOAA Fisheries West Coast region and Alternate U.S Commissioner to the IATTC. 

“We’ll continue this effort to ensure the sustainable harvest of bluefin for decades to come,” he said.

This story was originally published at NOAA on 25 June 2024, reposted via PACNEWS.