Atlantic bluefin tuna appear to be making a comeback, here in the Gulf of Maine and across the entire Atlantic.
Atlantic bluefin tuna are among the largest and fastest fish. They have long been prized by anglers for their tremendous strength and fighting ability.
Once scorned by Americans as not worth eating, bluefin were sold as pet food or simply discarded. Today bluefin tuna appears as sushi or sashimi on the menus of fine restaurants around the world, as well as in the display cases of ordinary supermarkets. That worldwide demand has made bluefin among the most valuable fish in the sea.
High value spurs intensive fishing.
Atlantic bluefin populations had been plummeting for decades, mostly because of overfishing. However, international conservation measures implemented on both sides of the Atlantic about 20 years ago — including restrictions on total harvest — halted the declines.
The International Union for Conservation of Nature, an environmental advocacy group based in Switzerland, publishes a Red List of Threatened Species. In September 2021, the group announced that it had taken Atlantic bluefin tuna off its endangered list and now considers it to be a “species of least concern” — two steps above endangered.
The effects of these conservation measures began to become evident in Maine about eight or nine years ago, when the big tuna began arriving in the Gulf of Maine in greater numbers.
“That’s when the fishing started to take off,” said Walter Golet, an associate professor at the University of Maine’s School of Marine Sciences. In 2011 he founded the university’s Pelagic Fisheries Lab in Portland. As the lab’s principal investigator, he ranks as an authority on highly migratory fish like bluefin tuna.
Mediterranean to Maine
Trying to understand the status of a migratory fish like bluefin is a daunting task. Knowing what’s going on in the Gulf of Maine is not enough. “You need to have a much broader perspective than just the Gulf of Maine,” Golet said. “They go everywhere.”
Bluefin tuna are extraordinary travelers. “If you could follow the movement of an Atlantic bluefin over the course of a year, they can easily swim 10,000 to 20,000 miles,” Golet said. “A bluefin never stops swimming.”
In addition to being marathoners, they are sprinters. When in pursuit of prey, they can put on short bursts of speed that may exceed 40 mph.
These powerful swimmers can travel back and forth across the Atlantic, and do so regularly. Astonishingly, in some years, as many as seven out of 10 fish caught in the Gulf of Maine were born in the Mediterranean.
The numbers fluctuate from year to year, with a peak of about 70%, Golet said.
Since bluefin often exhibit what researchers call “site fidelity,” many of these “Maine fish” will return to spawn in the Mediterranean, one of at least three spawning areas for the species. The other two known spawning areas are the Gulf of Mexico and the Slope Sea — the waters along the northeastern U.S. where the continental shelf slopes toward the deeper sea floor.
Small structure, big story
Samantha Nadeau manages the Pelagic Fisheries Lab and assists Golet, her boss, with fieldwork for their research. In late July, she and her team examined fish caught at the Bailey Island Fishing Tournament. In early September, they did similar work at the Boothbay Harbor Tuna Challenge.
On Sept. 3, a contestant in the Boothbay Harbor tournament caught a 740-pound bluefin in the afternoon. That’s bigger than the recent average in Maine — 400-500 pounds — but bluefin can be much larger. The world record is a few pounds shy of 1,500.
After the fish was hoisted off the boat and weighed, it was transferred to a nearby dock where Nadeau and her team were waiting. Before Nadeau went to work, Seth Richards, a tuna buyer based in Cundy’s Harbor, began testing the fish for quality and prepping it for sale. That included slicing off the tail and fins and decapitating it.’
Tuna heads contain small, hard structures called otoliths that are crucial to Nadeau’s work. Located near the fish’s brain, otoliths consist largely of calcium carbonate, like the shell of a quahog. In Boothbay, Nadeau probed the fish head with forceps to locate and extract the otoliths.
Under a microscope, sections of the otoliths reveal rings, each one indicating the passage of one year. The otoliths also reveal where the fish spent the early years of its life. These otoliths would later be analyzed in a lab for the presence of oxygen-18, an isotope of the more common form of oxygen.
Surface water in the Mediterranean has greater concentrations of oxygen-18 than the Gulf of Mexico or the Slope Sea, so higher levels of oxygen-18 in a bluefin’s otoliths suggest a Mediterranean birth.
Tagging is another important research tool. The Pelagic Fisheries Lab doesn’t have a boat for offshore tagging operations, but boat owners often collaborate with Golet and his colleagues to help them tag fish.
The researchers use high-tech tags called PSATs, short for pop-up satellite archival tag. When attached to a fish by a tether, PSATs collect information, such as depth, light level and temperature. Designed to detach after a prescribed time, they pop to the surface, where they transmit the collected data and the tag’s location to a satellite, which relays it to the research lab.
The tags cannot log location when attached to a fish swimming below the surface, according to Nadeau. But because they know where the fish was tagged and where the tag surfaced, researchers can process the data to estimate the entire track of the fish, she said.
How much is a bluefin worth?
Captain Bill Tranter knows the value of a bluefin tuna. He operates Midcoast Charters, out of Bailey Island. He is also president of the Casco Bay Tuna Club, which runs the annual Bailey Island Fishing Tournament.
Tranter said the price paid to the boats that caught the fish averaged about $4 per pound through the last six years. A year ago, it was about $5.
Fisherman get paid for the weight of the fish after the guts, head, fins and tail have been removed. The market weight is about 75% of the live weight.
The typical bluefin caught in Maine weights about 400-500 pounds, according to Tranter. The market weight would be about 300-375 pounds. At $5 per pound, the fisherman would receive about $1,500 to $1,875 per fish.
Not a princely sum, but a nice day’s work.
Complex process, ‘epic’ results
To effectively manage a population of fish that spans an entire ocean, it’s crucial to understand where they are born and where they roam. Scientists now know the Maine bluefin population likely would be much smaller without fish born in the Mediterranean. Or, as Golet put it, the Maine population is “heavily subsidized by fish from the eastern Atlantic.”
“Conservation management can’t be done in a box or a vacuum,” Golet said. What is done on the other side of the Atlantic to protect tuna is just as important as what is done along the East Coast, the Gulf of Mexico or Eastern Canada. It’s an international challenge.
The responsibility for assessing the status of the Atlantic bluefin population and allocating fishing quotas belongs to the International Commission for the Conservation of Atlantic Tunas. The commission has 54 member nations, each of which participates in a decision-making process based on consensus.
“You have to have everybody in agreement,” Golet said.
Clearly this isn’t an easy task. Yet the process seems to have produced results. Perhaps because of the greater abundance of bluefin across their range, Maine fishermen experienced a bountiful season in 2024.
“Last year was phenomenal,” said Richards, the Harpswell-based tuna buyer. “It started mid-June. They were here all season. It was a pretty epic season.”
This summer was a different story. Through late August, the fishing was difficult. “Good fishermen were not catching fish anywhere,” Richards said.
By the time of the Boothbay Harbor tournament in early September, the fishing had picked up. That left Richards thinking a good fall might offset the poor summer. “Hopefully more fish will arrive,” he said. “It could be very busy in the next couple of months.”
Richards doesn’t believe the poor fishing was the result of a decline in the overall population. “The biomass of fish is out there,” he said. “They just decided not to come (to Maine).”
The science seems to support that view. “All of the evidence suggests the western Atlantic population is doing well,” Golet said. That seems to be true of the stocks on both sides of the Atlantic. “Both are considered to be in good shape,” he said.
For now, these majestic travelers of the open sea have averted disaster. Foodies still can enjoy their sashimi. Recreational anglers can experience the thrill of a monster fish straining their lines to the breaking point. Commercial fishermen can support their families with a valuable catch. And everyone can take pleasure in the knowledge that these otherworldly creatures are still silently roaming the length, breadth and depth of the Atlantic.
