Stock Assessment: Pacific Bluefin Tuna Rebounds

Pacific bluefin tuna swim underwater. Photo: Adobe Stock.

NOAA Fisheries scientists are heralding the recovery of Pacific bluefin tuna as a major milestone, saying the species exceeded international rebuilding targets a decade ahead of schedule.

In announcing the achievement on June 25, NOAA Fisheries credited international organizations across the Pacific with cooperating to reverse decades of overfishing for the prized species.

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

The new stock assessment was finalized recently by the ISC at an annual meeting in Victoria, British Columbia. The assessment confirmed that the stock reached the second rebuilding target in 2021.

If current management measures persist, population growth is expected to continue increasing.

“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 Huihua Lee, a research mathematical statistician at NOAA Fisheries’ Southwest Fisheries Science Center, who led the work on the stock assessment in the United States.

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, Lee added.

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 the 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.

Commercial vessels in the United States 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 $2.2 million in on-the-dock revenue, data show.

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

By the time they’re 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 three to five 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.

The goal was to rebuild to at least 20% of the spawning stock biomass by 2034.