June 24, 2019 — Cod has long been a staple of the New England fishery, but this once-plentiful fish has declined in recent decades. Despite repeated attempts to rebuild the stock, assessments suggest that the species has not recovered, frustrating biologists and fishermen alike.
Although the species is managed as a single population, cod in the Gulf of Maine can be divided into two genetically-distinct groups. And according to a new study, understanding the unique behavior and lifecycles of these two groups may be the key to creating a better management strategy.
“These subpopulations are dramatically different from one another,” says Micah Dean, a doctoral student at Northeastern’s Marine Science Center who led the study. “And the mix of these subpopulations changes over space and season, and over time. This sort of complexity needs to be accounted for.”
Incorporating the differences between these two groups into population models could improve management decisions, says Dean, who is also a senior biologist for the Massachusetts Division of Marine Fisheries. And those decisions are vital to the survival and recovery of the fishery.
Both fisheries managers and fishermen have known that groups of cod in the Gulf of Maine gather to release and fertilize eggs twice each year, when the bottom temperatures are between 6 and 8 degrees Celsius (42.8 and 46.4 degrees Fahrenheit). In the last decade, researchers have confirmed that the fish spawning in May and June are distinct from the fish spawning in November and December. But there hasn’t been a clear way to incorporate this information into management strategies, so the animals have continued to be grouped together.