by Angela Herring

Marissa McMahan’s family has been com­mer­cial fishing in the Gulf of Maine for more than three gen­er­a­tions. “My grand­fa­ther used to go out and har­poon tons of bluefin tuna back in the day,” said McMahan, a second-​​year doc­toral stu­dent working in asso­ciate pro­fessor Jon Grabowski’s lab­o­ra­tory at Northeastern’s Marine Sci­ence Center in Nahant, Massachusetts.

Even­tu­ally the bluefin dis­ap­peared from Maine’s waters, fol­lowed by the cod. The family has watched as one fishery after another has col­lapsed, leaving only the lob­ster as a viable source of income. But in recent years they’ve started to see a rise in an alto­gether new species: the black sea bass, which used to only been seen on the south side of Cape Cod.

McMahan began lob­stering with her father when she was just 7 years old. Then, as a high school stu­dent, she got her own skiff and traps and used her fishing income to help put her­self through col­lege. After com­pleting her master’s degree at the Uni­ver­sity of Maine she returned to the decks and pon­dered the next step in her career. It was that summer of 2012 when she and her dad started noticing some­thing fishy.

“My dad had seen one or two sea bass in his traps before, but that summer we prob­ably caught 10 and that seemed out­ra­geous,” said McMahan, who didn’t even rec­og­nize the fish when she saw it. “That fol­lowing summer he prob­ably col­lected 35. It just kind of blew out of control.”

This trend has likely come about thanks to warming northerly waters due to cli­mate change. It’s also the inspi­ra­tion behind her doc­toral dis­ser­ta­tion work, which she’s now pur­suing with the help of a pres­ti­gious Grad­uate Women in Sci­ence fellowship.

The problem is that sea bass eat crus­taceans such as lob­sters. In the southern climes where they are most promi­nent, shell­fish such as shrimp and crabs make up more than 50 per­cent of the sea bass diet. When their habitat starts to overlap with that of juve­nile lob­sters, one has to wonder: will they start eating them, too?

“They’re a very aggres­sive, very ter­ri­to­rial species,” McMahan said. “They just chase every­thing away from their ter­ri­tory.” They’ve even chased her while she was trying to count and mea­sure them for her research. So it’s not unrea­son­able to think that the sea bass may chase away the lob­sters, too—if they don’t eat them first. Maine lob­stermen, she said, think the species is a major poten­tial threat to their livelihoods.

But here’s the strange thing: In the south, sea bass goes for twice as much money as lob­sters. The latter are becoming under­valued in the gulf, where they’re actu­ally over­abun­dant thanks to highly suc­cessful man­age­ment prac­tices. But there’s cur­rently no market for Maine sea bass, so the lob­sters remain king. “Whether or not it’s seen as inva­sive and harmful is going to define how man­age­ment comes into play,” McMahan said. She thinks there will be a tip­ping point, a moment when the lob­stermen won’t just see this as a threat but as a poten­tial new market. “But when will that happen? When will that change occur?”

For her dis­ser­ta­tion, McMahan is trying to get at the heart of that ques­tion. Not only is she studying the eco­log­ical impacts of the sea bass’s range expan­sion, she’s also inter­ested in the social side of the coin. She is working with fellow lab member Stephen Scyphers to design a series of paper sur­veys to admin­ister to lob­stermen, pol­i­cy­makers, and sci­en­tists about their per­cep­tions of the growing sea bass fishery. She’ll also be doing dive sur­veys in Mass­a­chu­setts, New Hamp­shire, and Maine to get a better esti­mate of the abun­dance and behavior of the fishery as it moves northward.

Finally, McMahan is part­nering with fish­ermen to col­lect sam­ples of sea bass that turn up in their nets and traps. She will use the sam­ples to gather infor­ma­tion about the sea bass’ age, size, and sex, as well as what they’ve been eating in recent days and over the past sev­eral months.

“Basi­cally the idea is to take all of these dif­ferent mea­sure­ments and com­pare them between regions,” McMahan said. She’ll use that infor­ma­tion to assess whether sea bass in the newer, more northern part of the range have a dif­ferent impact on the ecosystem than those in the range where they’ve tra­di­tion­ally been found. As she put it, “So in Maine where there’s a lot of juve­nile lob­sters, are they eating more lob­sters because they’re just so abundant?”

She hopes the sci­en­tific data cou­pled with the survey responses will pro­vide a holistic pic­ture of the future of the northern sea bass fishery. “I’m only studying sea bass right now, but what I’d really like is to test run what I’m doing as an overall model for how to mon­itor inva­sive and emer­gent species,” she said.

Essen­tially, this work should serve as a blue­print for future conun­drums in marine biology as cli­mate change con­tinues to push the lit­eral bound­aries of the nation’s fisheries.

Originally published in news@Northeastern on July 21, 2014.