Jeffrey Dubois: Trapping Green Crabs
On a sunny July day, Jeffrey Dubois hops into a boat at the dock of the University of Maine’s Darling Marine Center in Walpole. Wearing a blaze orange life vest, cargo shorts, T-shirt and a baseball cap, he starts the motor and heads out to the right side of the pier. He steers the boat toward one of four trapping stations he has set up along the shore in the Damariscotta River estuary. Accompanied by a fellow researcher, he hauls a trap from about 5 meters below the surface and finds it’s full of crabs.
Over the course of three days, Dubois will catch about 1,500 green crabs and between 100–200 rock crabs, also known as the commercially harvestable Jonah crab. He throws all them back. But before returning the green crabs to the sea, he measures characteristics such as abundance, species composition, size and sex in an effort to learn more about the invasive species he refers to as “feisty little tanks” and “voracious predators.”
Dubois, a senior from Norway, Maine, who is majoring in marine science with a concentration in marine biology, is trying to determine the most effective and efficient way to trap green crabs in the Gulf of Maine. He hopes information he gathers will help him and other researchers determine how green crab abundances alter with temperature changes and how to create a market for the plentiful creatures.
The green crab came to the Gulf of Maine from Europe in the mid-1800s. In the 1950s, the population exploded in the Gulf’s intertidal zones, causing declines in the state’s soft-shell clam industry, according to Dubois.
“The Gulf of Maine has no natural intertidal species of crab,” Dubois says. “As a result, they have been quite detrimental to our soft-shell clam industry, which developed without having a natural predator.”
The population increase in the 1950s was related to a rise in ocean temperature, and since the Gulf of Maine has been warming over the past few years, green crabs are starting to peak again, Dubois says.
Dubois says green crabs are a thermally regulated invader, meaning as the water gets warmer they thrive, and as the water gets colder they die in mass quantities.
“Our best bet is to chill down the Gulf of Maine, but with this whole idea of climate change, it’s probably not going to happen anytime soon,” he says.
The green crab is also one of the fastest species of crabs, according to Dubois. He says the larger they get, the more they can travel and the more they can eat. Although the crabs prefer a cobblestone habitat, mudflats can become accessible to the larger crabs, putting the soft-shell clams at risk.
“There’s not a lot that eats the green crabs,” Dubois says. “They’re very voracious, they eat a lot. Pretty much if there’s food out there, they’re going to find it, and as a result they’ve become quite a problem.”
There currently isn’t a market for green crabs, and Dubois thinks its mainly due to the crab’s small size — with the largest one he has seen coming in at 8.4 cm wide — and because they’re usually not found any deeper than 5 meters.
“The best thing we can do is open a market for them and just hope something fishes them all out,” he says.
Other researchers at UMaine are looking into ways to make green crabs commercially harvestable by incorporating them into fish food.
Dubois, who is collecting data until the end of the summer, is trying to find the best way to catch green crabs before moving onto more research where trapping will be used for sampling.
He is currently comparing two different baits — herring, a traditional lobster bait, and soft-shell clams — as well as two different types of traps. Dubois is using the Acer trap, a cylindrical trap designed by researchers to catch green crabs, and shrimp traps donated by a local fisherman. The shrimp traps are similar to a trap the Maine Department of Marine Resources used in the 1950s and ’60s to measure green crab abundances, Dubois says.
“What I’ve basically done is created a Punnett square,” Dubois says. “My hope is that I can figure out which bait catches the most amount of green crabs per trap.”
Although the Acer traps are designed for catching green crabs, Dubois is hopeful the shrimp traps and less expensive herring will prove to be an affordable option, by using equipment a lot of shrimp fishermen already have.
“Shrimping only happens in the winter, so there are a lot of shrimp traps out there that aren’t used during the summertime,” Dubois says. “If we were to open a market and the shrimp traps were effective in catching green crabs, people could fish for shrimp in the winter and fish for green crab in the summer.”
Dubois originally wanted to study the Asian shore crab, a more recent invasive species, but once he started researching at the center, he learned they hadn’t made it that far into the Gulf of Maine.
He then began looking for green crab studies and found a project being led by Brian Beal, a marine ecology professor at the University of Maine at Machias, that focuses on measuring abundances over a few sites in Maine. With the help of his capstone adviser, marine science professor Bob Steneck, Dubois got involved with Beal and his research.
“Once I can figure out how to best capture green crabs, the doors that open for my research are almost infinite,” Dubois says. “Eventually, once Asian shore crabs make it up here, I want to see which one is the better invader.”
After earning his undergraduate degree, Dubois plans to attend graduate school to earn his master’s — possibly in coral reef ecology, following in the footsteps of Steneck — and eventually get a Ph.D.
“I don’t want to get my Ph.D. yet because I can get it at any point in my life. I only have a youthful body until I’m — oh, I don’t know — 40 or 45,” Dubois says.
In the near future, Dubois hopes to continue to conduct research, enter the workforce and start making connections.
Dubois recalls wanting to be a marine biologist in elementary school, but let that dream fade in his pursuit to become a doctor.
“I went into college with biochemistry and a minor in pre-med and I was gung-ho that I was going to be a doctor,” Dubois says. “I’m first generation to go to college, so why not become a doctor? Go big or go home, right?”
After his third semester in the program, Dubois, who became a CNA at age 16 and started working in a hospital at 18, decided being a doctor wasn’t what he wanted.
“I remembered seeing a poster for the Darling Marine Center’s Semester by the Sea my freshman year in my Biology 100 class, and I thought ‘Wow, that would be so cool to be able to do that.’ And two years later I decided to switch to marine science. It was a shot in the dark, something I wasn’t really sure of, but I haven’t looked back since,” Dubois says.
Dubois, who has a full-time job at Maine Kayak and recently picked up a second job at Glidden Point Oyster Farm, says finding time to do research on top of working seven days a week can be challenging, but it’s worth it. He sees the study as a great opportunity to learn valuable research skills, such as “being able to roll with the punches” when it comes to science and enjoys studying at the center.
“This is anywhere and everywhere that I’d want to be and now I’m doing that Semester by the Sea program that I saw on that poster freshman year,” Dubois says. “It’s kind of like you gotta see what you want, then you’ve gotta take it.”