Thinner isn't always better.
Thinner isn't always better.
A new study at the University of New Hampshire, supported by data from the Yankee Fisherman's Cooperative in Seabrook, shows bluefin tuna are losing fat, and nobody knows why.
The study is the first done in the United States and confirms what fishermen have long observed: bluefin tuna are no longer fattening up during their annual summer migration to the Gulf of Maine.
Scientists are trying to determine what this means for the ocean and the environment. The economic consequences are already known.
Local fishermen, said Bob Campbell, manager of the Seabrook co-op, have stopped going out for bluefin.
"The quality of the bluefin has gotten progressively worse," Campbell said. "The catching is so poor; it's a waste of time."
The bluefin, among the largest of tunas, is at the top of its food chain, said Walter Golet, a doctoral student at the University of New Hampshire who did the study.
"I think because it's happening in a top predator ...," Golet said, "historically speaking, we have such little data, we can't go back 200 years. We don't know if this is part of an ebb and flow."
Canadian studies have shown a similar decline.
Bluefin has been overfished Atlantic-wide, Golet said.
The lack of fat could mean there's something changing in the bottom of the food chain. Studies suggest the Gulf of Maine is getting warmer, which wouldn't harm the warm-blooded bluefin, but could affect what it feeds on, Golet said.
"We don't know the reason," he said. "I'm working on that now."
Future studies will try to determine a cause.
Golet, 32, of South Berwick, Maine, expects to receive his doctorate next year. He is working under Dr. Molly Lutcavage, head of the Large Pelagics (open water) Research Center within the Zoology Department at UNH.
The bluefin study, published in the July 2007 edition of the NOAA Fisheries Bulletin, documents the quality of bluefin brought to the Yankee Fisherman's Cooperative since 1991.
UNH contacted Campbell for information four to five years ago. Golet said they were amazed when Campbell pulled open a drawer at the co-op holding records on bluefin going back 14 years.
The UNH laboratory turned Campbell's numbers into a probability chart on the likelihood of a fisherman catching a quality bluefin.
"Our lab ran the numbers," Golet said. "When we saw the results, we were taken aback."
The chart tracks the quality of bluefin from 1991 to 2004, in grades of C or worse, C-plus, B-minus and B. There is no "A," said Golet, since by 2004 no bluefin met that grade.
In 2004, 226 commercially caught bluefin were brought to the co-op, Golet said. Only two met the quality for a grade "B" fish. In 1991, the probability of catching a B-grade bluefin in the month of September was 40 percent.
In September 1991, a fisherman had an 8 percent chance of catching a C-plus quality bluefin. By 2004, that likelihood had increased to 70 percent.
What's missing in the fish is the fat, or lipids, Golet said.
"Lipids are king. ... "Typically, in June and July, most fish have a low fat content. In June, they're coming into the Gulf of Maine lighter than in previous years."
The bluefin migrate into the Gulf of Maine in early summer to feed. As the season progresses, they are supposed to fatten up on Atlantic herring, mackerel, sand lance, and sometimes bluefish. The Atlantic herring is in high abundance, as opposed to stocks of river herring, which are in decline.
Overall, there's a high abundance of fish for the bluefin in the Gulf of Maine, Golet said, though this doesn't mean specific feeding areas couldn't have a lower quantity of food.
After feeding, the bluefin leave the area to spawn.
The prime season to catch them is September through the end of October, when the bluefin are well fed and still around the big fishing areas.
Economically, the fat is needed to give the fish marbling, as in the best beef, Golet said.
Bluefin is not used in canned tuna. Even tuna steaks are often yellowfin. Bluefin is considered the prime cut, comparable to the best beef fillet. It is most often seen as sushi, and its primary market historically has been Japan.
Fishermen used to get $5,000 to $10,000 for each bluefin, depending on size and weight. The domestic market couldn't compete with the prices paid by the Japanese market, Golet said.
The rising price of fuel and skinnier bluefin equate to smaller profit margins. It's now more economical to ship 500 pounds of fish domestically, Golet said.
"Things are subtly changing in that the U.S. is the bigger port," he said. "More is sold locally."
What the changes in one species means for the planet is unknown and could be part of a bigger picture.
"It's kind of like a big puzzle," Golet said. "We're only working on a little part of it."