Fishermen and marine ecologists have sounded alarm bells about the rapidly expanding green crab population along the coast for years. Although the state recognizes the threat green crabs pose to fisheries, Maine has not implemented a statewide system to monitor the invasive species’ population and range or done much to combat it beyond the local level.
Work on the green crab population presently happens at the local level with support from the Department of Marine Resources.
The state works with locals on a case by case basis using techniques like crab trapping, protective netting over juvenile clams and crab population surveys at specific locations, said Meredith White, the Nearshore Marine Resources Program Supervisor for the Department of Marine Resources. But there’s no concrete data available right now on just how much the problem has grown in recent years, White said. The last time data was gathered was 2013.
The state is currently developing protocols for long term climate change monitoring starting in 2024, which would include “more consistent and widespread tracking” green crabs, White said. But the threat posed to Maine’s fisheries will likely only get worse as green crabs continue to spread, she said
“Based on the experiences of the past decade, it does appear that continued increases in winter water temperatures will lead to further green crab population growth,” White said.
Maine could be doing more. Here are a few that experts say the state should consider for managing green crab populations.
Commercial use
One of the most discussed ways to put a dent in green crab populations is to use them commercially. Creating a commercial market and demand for green crabs would mean they get harvested and used, controlling the population.
That’s been the major goal of GreenCrab .org, a nonprofit dedicated to building up a commercial fishing industry for green crabs and getting them onto menus across New England, said Mary Parks, the organization’s founder.
In other countries, softshell green crabs are considered a delicacy, and they can be used in a wide variety of meals both for home cooking or in restaurant kitchens. Lobsterman and restaurant owner Sadie Samuels added green crab to the menu at Must Be Nice Lobster in Belfast earlier this year, and right now hers is the only restaurant in Maine to add green crabs to its permanent offerings. Getting more chefs to add them to menus would help because there would be more need to trap them. It could also create a model for other places dealing with the growing problem, Parks said.
Green crabs don’t have to just go straight to the table, either. There’s been a number of creative approaches to utilizing green crabs from the Gulf of Maine. They’ve been turned into pet food, they make an excellent fermented fish sauce and they’ve even been turned into whiskey. Cambodian immigrants in southern Maine have been driving the green crab market by using them in a number of traditional dishes.
Parks said even getting them on menus and developing the commercial industry is only one part of the puzzle here.
Their population grows too rapidly, with a single green crab producing up to 185,000 eggs per year, Parks said, and they can survive a wide range of temperatures and environments while other crustaceans continue to be impacted by climate change through rising water temperatures and ocean acidification.
“The reality is that we’ll never be able to get rid of green crabs by fishing them,” Parks said.
A unified response
Parks views the rapid expansion and destruction wrought by green crabs along the upper east coast as a cautionary tale for other places that are just starting to experience the first wave of the invasion.
The scale of the green crab threat to fishing industries is massive, and in other states like Alaska that are only recently experiencing their first sightings of the invasive species, the response has been swift.
Wildlife Biologist Linda Shaw with the National Oceanic and Atmospheric Association Fisheries for the Alaska Region has been on the front lines of the invasion since day one. She was a member of the survey group that first recorded finding a green crab shell in the Annette Islands Reserve belonging to the Metlakatla Indian Community in July 2022.
“It wasn’t long after that that the first live ones were caught and we knew we had an infestation,” Shaw said. “It was a combination of being glad we had found them because we expected them to show up and being really bummed out that we found them.”
Green crabs haven’t reached mainland Alaska yet, Shaw said, but the state has responded quickly in collaboration with local governments and tribal officials to prepare trapping and survey programs, while NOAA has begun pilot programs for a number of pilot programs for prevention and early protection.
The urgency in the statewide response comes from the potentially massive threat to Alaska’s fishing industries, combined with a number of subsistence based native cultures that see the high risk to their food stocks, Shaw said. Now that the species is in Alaska, it’s likely there to stay, but there are efforts underway to contain the crabs as much as possible.
“I like to think of myself as an optimist and I hope for the best, but realistically it would be pretty tough to eradicate them,” Shaw said. “It’s probably more realistic that what we could hope for is to get that population under control and prevent it from spreading further.”
While using them in the seafood stock is a small way to help, to really put a dent in the population Samuels thinks there needs to be a more organized effort. She’d like to see a future where the state of Maine collaborates with fishermen and scientists to incentivize catching green crabs, whether it’s for the dinner table, to add to compost piles or something else.
Kill the kids
While efforts in Alaska have focused primarily on preventative methods, NOAA has also just begun a pilot program testing the effectiveness of canine green crab detection, Shaw said.
The method has been successful in sniffing out invasive Zebra mussels on the west coast, and Shaw said there’s a number of ways dogs might be able to help deal with green crabs.
Not only could their sense of smell help find green crabs along wide ranges of coastal area quickly, which is useful for early detection, but dogs could play a meaningful role for places that already see an infestation. If they could be taught to sniff out female green crabs carrying eggs they could be a critical part of the process for dealing with population growth by targeting the species at the beginning of their life cycle, Shaw said.
In Washington state, following a mass trapping effort that was intended to cut down on green crab, the state saw their population quickly rebound, Shaw said. That’s because green crabs eat each other, and by only targeting adult green crabs, the high number of juveniles were able to grow without the same level of predation they’d typically experience, she said.
But eliminating egg carrying females, in combination with extensive trapping, could give states a better shot at permanently denting the population, she said.