BOSTON (AP) — State officials and shark experts moved quickly to reassure beachgoers Monday after a tuna boat snagged a great white shark, the first confirmed sighting in Massachusetts waters this summer of one of the sea's most feared creatures.

The juvenile shark — 6 to 7 feet long and weighing an estimated 150 pounds — was pulled up by Gloucester-based Sweet Dream III on Saturday some 20 miles off the coast in the rich fishing ground known as Stellwagen Bank.

"Something kind of crested up out of the water ... and we pretty quickly realized it wasn't a tuna," Bruce Sweet, skipper of the vessel, said in an interview with the Associated Press. "It was a shark, seeing the dorsal fin and the tail."

When the shark went for some live mackerel bait, the crew went into "fish-fighting mode," Sweet said, and it took about 15 minutes to bring the great white under control. The crew then put a tag on the shark and released it back into the ocean.

"There were high fives all around," he said.

State Secretary of Environmental Affairs Ian Bowles said sharks are elusive and hard to track, but he was more certain on the potential danger to humans: "For common-sense swimmers, they don't pose a threat," he said.

Common sense, he explained, means not swimming amid a gathering of seals, a favorite food of great whites.

The last fatal shark attack off Massachusetts was nearly 75 years ago. Indeed, the state's most famous shark attacks are fictional: The 1975 blockbuster film "Jaws" was shot on Martha's Vineyard, and the movie is credited with creating a Hollywood-style mythology around great whites that scientists say is not backed up by fact.

Still, experts acknowledge that visits by great whites to New England waters may be on the rise.

"We've been seeing a slow increase over the past 10 years in the number of credible sightings," said Dr. Greg Skomal, a biologist with the state Division of Marine Fisheries, who added that most perceived great white sightings turn out to be something more benign — basking sharks, for example.

Skomal said great whites enjoy feasting on gray seals, the population of which has exploded since protections were put in place in the 1970s. Monomoy Island off Chatham has become one of the more popular gathering spots for gray seals, and swimmers in the area were warned last summer after several sharks were spotted.

Officials said they anticipate more great white sightings this summer but did not foresee beach closings, though Bowles said those decisions are generally made by towns.

The tag placed on the shark would only be useful to scientists if the animal were ever recaptured.

A year ago, state biologists successfully attached more sophisticated electronic tags to five great whites off Cape Cod. The satellite tracking devices produced a wealth of information about the migratory habits of the sharks in the northern Atlantic Ocean.

Skomal is hopeful that more of the electronic tags, which send data via satellite when they detach and surface, can be placed on sharks this summer.

Data from four of the great whites tagged with the help of a harpooner last summer (the fifth device surfaced prematurely) revealed that the sharks had left southern New England by October and wintered in waters off northern Florida.

The last of the tags to surface was on April 15 off North Carolina.

Among the more surprising discoveries was that the great white seemed to have a well-defined comfort zone, spending more than 80 percent of their time in 59- to 67-degree water, Skomal said.

"That's a really narrow temperature range," he said.

Scientists were also mildly surprised that Atlantic great whites tended to hug the coast — staying within about 200 miles. Pacific sharks have been known to stray as far as Hawaii after feeding off California.