Every year Island anglers eagerly await the arrival of the Atlantic bonito. The steel blue, tuna-shaped fish, marked with a series of dark stripes that cut across the upper part of its abdomen, ordinarily begins to erupt along the surface of local waters in mid to late summer.

This year the bonito arrived early. The first sighting was in late June.

Island fishermen greeted the news with equal parts cautious optimism that bonito stocks are rebounding, and concerns about the changing ecosystem of area waters. There are questions too about regulations and possible weakness in federal oversight of the local fishery.

When fully mature, bonito can weigh up to 12 pounds, but the average fish caught weighs closer to five pounds. Pound for pound, they are one of the strongest fish in waters along North Atlantic Seaboard. Their strength and the sushi-grade quality of their meat makes them one of the more sought-after recreational fish in local waters.

Cooper Gilkes 3rd, owner of Coop’s Bait & Tackle and longtime Island angler, confirmed that the bonito were “starting to sprinkle in” around Oak Bluffs and Menemsha in late June. According to Mr. Gilkes, July 28 is the day that comes to mind when he starts to prepare for the arrival of the bonito, which return along with warmer waters.

But as Greg Skomal, recreational fisheries program manager for the state Division of Marine Fisheries (DMF), made clear: “There is a lot we don’t know about the fish.”

He said Atlantic bonito, though predominantly found in Nantucket Sound and off the south shore, technically falls under the purview of the National Oceanic and Atmospheric Administration (NOAA), the federal organization that oversees all commercial tuna fisheries.

But the bulk of information about bonito in fact comes from the DMF. Though the agency has no regulatory power over bonito, it is more familiar with the fish on a local level.

“Usually the species that are prioritized in terms of research are the ones that are harvested heavily, both commercially and recreationally . . . codfish, haddock, bluefish, striper . . . bonito is kind of a small player when it comes to commercial landings,” Mr. Skomal said.

He said it appears as though the fish has slipped through the cracks of NOAA, making it under-researched and unregulated. For example, there is no bag limit or legal keeper size for bonito.

“I don’t think it’s a lack of research as much as a lack of management,” Mr. Skomal added. “It’s hard to say what’s going on this year because we simply don’t know enough about the natural history and biology of this animal.”

Bill Hoffman, a marine biologist with the DMF, was cautious about drawing conclusions, but said the early arrival of bonito could be due to warmer water temperatures earlier in the season after a mild winter.

“Everyone wants to jump on global warming to explain it,” said Ross Kessler, public access coordinator for the DMF. “It could also be due to the bait source,” he said, noting an increase in sand eels in local waters and around his station in New Bedford.

“If 30 bonito swim through and find a good bait source, they’re staying as opposed to leaving,” Mr. Hoffman said.

Mr. Skomal framed a similar opinion.

“It could be an indication of climate, but it could also be an indication of a growing stock,” he said.

Mr. Gilkes agreed. “They’re spreading both north and south and to me that means a larger stock,” he said, noting confirmed reports of bonito in North Carolina three weeks ago and other reports of runs along the north shore last year.

Mr. Skomal said there was an abnormally large young-of-the-year population last summer, which would contribute to a larger and stronger mature stock this year and hopefully in the years to follow.

Mr. Gilkes said that despite potentially rebounding stocks, this is no time to relax on pushing for regulations for the fish. Like many Island fishermen, he said he remembered a time when the waters were filled with bonito. But unsustainable fishing practices, where bonito are caught in fish traps or drag nets and sold as bycatch for lobster bait, have greatly affected the fishery over the years.

Mr. Gilkes said he thinks bonito should be regulated as a game fish, which would limit its ability to be sold as bycatch on the commercial market.

“Having no regulations doesn’t make any sense,” he said.

Mr. Skomal said the early arrival of the bonito provides opportunity for learning.

“It’s an interesting phenomenon that bonito are here so early,” he said.

“We should take it as a positive sign, but it’s these kind of odd years that help you learn about the species.”