Your Questions, Answered: Are Atlantic bluefin tuna doing well?

By Melissa Waterman

Chris Weiner is passionate about Atlantic bluefin tuna. After fishing into the late hours the day before, he is driving to Snug Harbor, Rhode Island, to pick up small tuna for genetic testing, and talking a mile-a-minute about his favorite subject, tuna.

Atlantic bluefin tuna. Photo courtesy of GMRI.

Weiner is the executive director of the Bluefin Collaborative; his father Steve is its president. The non-profit organization’s mission is to improve Atlantic bluefin tuna science and management by sourcing data, funding critical research, and educating the public and decision-makers about the species.

“There’s a lot of tuna now, all sizes, everywhere,” Weiner said. “The problem is that we don’t have enough data because we can’t count them.”

Atlantic bluefin tuna, known as a ‘highly migratory species’, is managed as two stocks by the International Commission for the Conservation of Atlantic Tunas (ICCAT). The western stock is harvested by the United States, Mexico, Japan, and Canada while the eastern stock is fished by countries across the Mediterranean basin and eastern Atlantic. ICCAT divides management of these two stocks at the 45oW meridian, setting separate catch limits and management measures for each stock.

Bluefin tuna are largely caught by purse seines in the Mediterranean and eastern Atlantic. Catches in the Mediterranean during the 1990s and 2000s skyrocketed, peaking at 60,000 tons in 2007, nearly double the scientific recommendations at the time. In addition to harvesting smaller tuna, many of which had not yet spawned, companies also caught and kept young tuna in offshore pens in order to grow them to larger, more valuable sizes.

In the U.S., commercial fishermen are restricted to harpoon and line-caught tuna, or pelagic longlining. In the U.S. the minimum legal size for bluefin tuna is 73 inches.

A recently published study has shown that the conservation measures in western Atlantic have helped the Mediterranean stock recover from decades of overfishing. “Ensuring the Future of Atlantic Bluefin Tuna”, published in Proceedings of the National Academy of Sciences, drew on electronic tagging data and decades of catch data.

From 1996 to 2025 scientists from the U.S., Canada, Ireland, Norway, and Spain deployed electronic tags on 1,720 bluefin tuna. The tags gathered data on where and when the fish migrate, where they feed, and when bluefin tuna enter and leave known spawning areas.

The results showed that many bluefin tuna move from eastern Atlantic and Mediterranean waters to the western Atlantic to forage and grow on abundant prey like mackerel, herring and menhaden. These fish often remain in the west for several years before returning to the Mediterranean Sea or spawning in the Slope Sea (an area off the northeast Continental Shelf and the Gulf Stream). Bluefin tuna that were born in the western Atlantic, however, tend to stay west of the 45oW management line.

The team also analyzed regional catch data dating back to 1950 to better understand the fishing pressure on bluefin tuna in the different regions. During that period 55% of the total catch was caught in the Mediterranean Sea, while 11% was caught in the entire West Atlantic (all regions west of 45°W).

In the past 30 years, the difference between the two areas has become even more extreme; the Mediterranean now makes up 72% of the catch across the entire Atlantic.

The study found that bluefin from the Mediterranean areas that managed to escape the region without being caught and migrated to the east coast were able to live longer, grow larger, and contribute more offspring to the eastern population.

For more than 45 years in the U.S. and Canada, the bluefin tuna fishery has had quotas, typically a tenth of those in the eastern Atlantic region. Strong conservation measures, including size limits and prohibitions on targeted fishing in the Gulf of Mexico, have protected the stock.

The results can be seen on the water. Weiner has seen a marked uptick in bluefin in the offshore areas where he fishes. “There’s so many fish now that we can’t make money,” he said. “Last year there were 51 boats and our quota was 54 tons. We caught the quota by the end of June.”

The tuna may be benefitting not only from conservation measures but also from increased water temperatures along the Eastern seaboard and an abundance of bait. A robust menhaden population, as well as growth in mackerel and river herring stocks, have given the tuna a buffet of fat-rich prey fish to eat. Off the mid-Atlantic states the migrating fish are finding abundant squid and sand lance.

“There are lots of 100 to 120-inch fish now. Catch a few of them and you are done,” Weiner said, referring to the weight of the larger fish.

The success of management measures on this side of the Atlantic is a positive story, but current commercial regulations are a mixed bag for Weiner. Under a general permit, from June 1 to June 30 commercial fishermen are allowed three fish per vessel per day or trip. Starting July 1 through August 31, the limit is one fish per vessel per day or trip. ICCAT increased the U.S. quota for this year to 1,509.98 mt from 1,316.14 mt.

Through the Bluefin Collaborative Weiner wants to collect as much data as possible to determine where the fish come from, if they are spawning throughout their range, and if current regulations accurately reflect the status of the stock.

“The U.S. is working hard to get better data because right now its management is based on past landings,” he said. “That’s why I’m driving to R.I. today.”

This article was made possible with the support of Farm Credit East Ag Enhancement grant.