Warming ocean temperatures are boosting the populations of small blob-like creatures in Maine’s coastal waters, causing problems for fishermen.
The small invertebrates, several species of which are invasive, are attaching themselves in large numbers to lobster traps and aquaculture equipment, at times creating a major hassle for harvesters as they try to tend to their gear.
“The month of September, they come on like gangbusters,” Hilton Turner, a lobsterman and chair of Stonington’s harbor committee, said about the tunicates, which are better known as sea squirts.
“Every year gets a little worse,” he said.
Brian Beal, a marine scientist who teaches at University of Maine’s Machias campus and runs the Downeast Institute, an aquaculture research organization on Great Wass Island, was more blunt about the creatures.
“They’re a pain in the ass,” Beal said.
They can grow so heavily on mussel ropes and oyster cages that they threaten to suffocate the creatures that sea farmers are trying to cultivate, he said.
“Sea squirts have exploded in the Gulf of Maine over the past decade or so,” Beal said. “They’re just a huge nuisance.”
The creatures’ increasing presence in the Gulf of Maine is one of several shifts in species being found off Maine’s coast that scientists say are being fueled by climate change and an overall increase in the gulf’s water temperatures.
Along with the increasing threat of more severe storms, Maine’s fishing industry is being disrupted by the gulf’s changing populations. Invasive species such as black sea bass and green crabs are showing up in greater numbers, while other traditional Maine species such as cod, northern shrimp and herring are being driven out
Even lobster — which by far still remains the biggest and most valuable fishery in the state — is not immune from the gulf’s changing conditions. The industry has had a 30 percent drop in statewide landings since it peaked in 2016, when 132 million pounds of lobster were brought ashore.
Emily Lancaster, who teaches marine science at Eckerd College in Florida and got her PhD from University of Maine, said there are roughly a dozen different species of tunicates in the Gulf of Maine, where she did her graduate research. More than half of which are believed to be invasive species from somewhere else, she said.
Some species are colonial in nature, such as a variety that looks like pancake batter and is sometimes called “sea vomit,” she said. Other non-colonial varieties — ciona intestinalis, or “sea vases,” and a European variety called ascidiella aspersa — are among those that grow on fixed fishing gear.
“They are a big problem for fishermen,” Lancaster said. “Climate change is definitely a factor.”
Turner said sea squirt numbers fluctuate with the seasons, peaking as the busy fall lobstering season begins in earnest. They are more likely found in shallower water, clogging the mesh and netting of traps and even attaching themselves to ropes that connect the traps to surface buoys, he said.
“It makes them wicked heavy,” Turner said of hauling tunicate-encrusted traps to the surface. The sea squirts can double the weight of a trap, making them difficult to lift out of the water and limiting the number that can safely be taken on board, he said.
Lobstermen use different techniques to try to remove the squirts. Some set the traps in boiling hot water tanks on their boats, some try immersing them in salt-saturated water, and still others blast them with a power washer, which can be time-consuming, Turner said.
“If we could find a predator for those things, that would be excellent,” the fisherman said.
Beal said continually having to remove tunicates from fishing gear can consume a lot of time and money. Through trial and error, researchers have worked with mussel farmers to figure out how to heavily seed grow ropes with mussel larvae to help limit tunicate outbreaks, he said.
“They are out-competing them for food,” Beals said of grow sites where sea squirts have proliferated. “Most farmers are ripping their hair out to keep these things from getting on their gear.”
The state Department of Marine Resources, which regulates Maine’s commercial fisheries, does not have any programs aimed specifically at tunicate research or management, but it does have a web page dedicated to information about the creatures. Spraying them with white vinegar is effective in killing some species but not others, according to the agency.
“Tunicates cannot survive drying out, so the best way to eliminate them from gear is to remove the gear from the water and scrap off the tunicates after they have dried,” the web page says. “They will also not survive significant rain events, so leaving gear in the rain may also reduce their presence.”
Lancaster cautioned that trying to contain the spread of sea squirts is not a straightforward problem to solve.
Some varieties are known to spawn as a reaction to stress when the traps they are attached to are hauled to the surface, she said. Plus, scraping tunicates off gear and then dumping them back in the water is not a death sentence — especially for colonial varieties — and could result in greater dispersal of sea squirts on the ocean bottom.
“You could potentially make the problem worse,” she said. “It’s probably not going to be a one-size-fits-all solution.”
Beal said that as long as ocean temperatures in the Gulf of Maine continue to rise, or even stay at their current levels, managing sea squirts will be a challenge.
“If only we could get a winter like 1963,” Beal said, which was especially cold and snowy in much of the Northern Hemisphere. “But I don’t see that happening anytime soon.”
