Researchers at the Wells National Estuarine Research Reserve have been trapping blue crabs and plan to monitor them in Casco Bay this summer. Credit: Courtesy of Ben Gutzler

The appearance of blue crab in Maine over the past couple years has researchers wondering if the prized southern crustacean is making a new home up north.

Known for their bright blue claws, blue crabs are one of the most valuable commercial fisheries in the Chesapeake Bay. While not unheard of, sightings in Maine are rare, and the species historically does stray much further than Massachusetts.

But scientists in southern Maine say they’ve found dozens of blue crabs in the salt marshes off Wells, prompting them to investigate if the species is extending its habitat north as the Gulf of Maine warms.

If it is, there’s potential for a new fishery in Maine, though there is also tremendous uncertainty around how the highly predatory crab would interact with local species, including the lobster — the bread and butter of Maine’s fishing fleet.

“It’s a little bit exciting and alarming at the same time,” said Jason Goldstein, the research director at the Wells National Estuarine Research Reserve.

The research team at the reserve first got an inkling that blue crab could be settling farther north in 2019, when they saw a dead crab in their marshes. But that wasn’t too out of the ordinary. The occasional blue crab has been seen in the Gulf of Maine going back to the 1800s, and they’ve even been found as far north as Nova Scotia.

The populations historically haven’t settled north of the southern edge of Cape Cod, though, so when the reserve stumbled across more during an annual survey of the Webhannet River Estuary in 2020, it piqued the curiosity of Laura Crane, a research associate at the reserve.  

“I looked down in a salt marsh pool in September, and there were seven adult blue crabs swimming around,” she said. “I was like, ‘They don’t belong here.’”

With that discovery, the researchers put out crab traps around the estuary and ended up trapping 30 blue crabs between September and December 2020. In 2021, they caught 48 between April and November.

It’s not just adult crabs, either. Crane said they’ve also seen baby crabs. It’s unclear if the younglings hatched off Maine’s coast or flowed there from somewhere else, but it could be an indicator that the crabs are living in southern Maine.  

Another sign that they could be established here is the time of year the adult crabs were found. The reserve caught blue crabs just after the estuary thawed out last spring, leading scientists to believe that the crabs didn’t just swim north but stayed in Maine over the winter.

But 2022 has thrown a curveball.

With monitoring ramped up, Crane hasn’t caught a single blue crab so far this year. She also hasn’t seen egg-bearing female crabs during the past three years. That has left the team wondering if their discovery in 2020 and 2021 may have just been an anomaly.

Crane theorized the species was able to stay in past winters because the weather wasn’t as harsh.

“It’s interesting and makes you wonder what’s different this year,” she said.

Climate change is expected to add new species to the Gulf of Maine in the coming decades and raises concerns about what that could mean for its current inhabitants. There hasn’t been a lot of historical overlap between lobsters and blue crabs, which Crane said will eat pretty much anything they can get their claws on.

“If blue crabs become more common, how does that bode for American lobster?” Goldstein said. “They are an aggressive species, and we don’t know if a blue crab would eat a lobster or compete for space.”

Southern Maine lobstermen do haul up blue crabs on occasion, but it’s still an oddity.

Laurin Brooks caught one in his traps off Wells last year and had heard of about four other instances of people catching them. David Kaselauskas, a lobsterman from Kittery Point, caught a couple blue crabs a few years back, but even with warming waters, he hasn’t seen them in any great numbers.

The reserve is planning to expand monitoring into deeper waters this summer. Crane’s enlisted volunteers at docks in Portland and other locations in Casco Bay that will put out traps to see what they find.

Any blue crabs they catch will be tagged with trackers, so Crane can monitor their patterns and see if a northward trend has started.

“The main question is are they here to stay,” Crane said. “The Gulf of Maine is trending warmer, so even if this particular population was ephemeral, I wouldn’t be surprised if they did extend their range into southern Maine.”