Impact of Black Sea Bass in Gulf of Maine Remains Unclear

With the Gulf of Maine warming at a rapid rate, its waters are opening up to a host of new guests, one of which is causing quite a stir. Meet the black sea bass, a favorite fish of recreational fishermen but a cause of concern to others, even being labeled the new “poster child for climate change.” Lobstermen in Maine as well as marine scientists are asking the same questions: what exactly is this mysterious black sea bass and what are the implications of its presence in the Gulf?

Black sea bass (Centropristis striata) call Atlantic coastal waters their home, ranging from the Gulf of Mexico to southern Massachusetts. They are protogynous hermaphrodites, which means that the fish are all females for the first part of their life, then change into males at 2 to 5 years of age. This unique characteristic complicates studies on the species, leading to uncertainty about its stock size as well as its response to commercial harvesting.

The northern black sea bass stock migrates seasonally and spawns in New England waters in the late summer. In fall, when coastal bottom water temperatures approach 44.6o F., the fish will move offshore to wintering areas at depths of 240 to 540 feet. In spring, when bottom waters exceed 44.6o F., black sea bass move inshore to shallow water. Historically, black sea bass have not been found north of Cape Cod due to cooler water temperatures; however, as the Gulf of Maine warms, their northern range is expanding into Maine waters. Black sea bass eat small fish, mussels, clams, and, of concern to lobstermen, juvenile lobster. Scientists so far are not sure just how much lobster the black sea bass eat.

Black sea bass are managed by the Atlantic States Marine Fisheries Commission (ASMFC) which sets an annual quota and then allocates that quota on a state-by-state basis. A benchmark stock assessment in 2016 found that black sea bass were not being overfished. The quota is divided nearly equally between the recreational and commercial fisheries. In 2016, commercial fishermen caught approximately 2.49 million pounds, less than the 2.71 million-pound quota. Otter trawls, gill nets, and fish pots and traps account for the majority of black sea bass landings in most states.

Maine is allocated 0.50% of the annual quota (13,559 pounds), compared to Massachusetts, which receives 13% (352,525 pounds), a reflection of the fact that the species once rarely ventured above Cape Cod. How much of Maine’s quota is landed each year is unclear. Since so few Maine fishermen land the fish, the landings data remain confidential, explained Jeff Nichols, communications director at the Maine Department of Marine Resources.

Studies by the Commercial Fisheries Research Foundation in Rhode Island on black sea bass abundance in that area indicate that the population is expanding. Working with nine Rhode Island fishermen using eight different types of gear, the Foundation has been sampling the fishermen’s catches since December 2016. The conclusion? “Black sea bass are caught in basically everything that goes in the water,” said executive director Anna Malek Mercer at the Maine Fishermen’s Forum in March.

Unfortunately, studies of black sea bass in the Gulf of Maine are limited and preliminary at best. In order to understand the ecological impacts of their increasing range, it is crucial to get a better understanding of their abundance in the Gulf as well as shifts in distribution. For now, the implications of having more black sea bass in the Gulf of Maine remain a mystery.