[Press Release] New genetic tools developed to understand Atlantic cod populations in the Gulf of Maine

(GLOUCESTER, MA) The Atlantic cod (Gadus morhua) is deeply rooted in the history of Massachusetts and remains a critical coastal resource throughout New England. The iconic species is recognized as the official state fish of Massachusetts and is immortalized in a wood-carved, five-foot effigy titled “Sacred Cod” that hangs in the House of Representatives chamber of the Massachusetts State House.

In addition to its historical status in Massachusetts, the Atlantic cod has been embraced by Gloucester Marine Genomics Institute (GMGI) to adorn the outside of its research facility on Gloucester Harbor. Shortly after becoming incorporated in 2013, GMGI turned to the historic fish as a research subject in their initial investigations. In 2021, building off of GMGI’s first published article, fisheries researchers at GMGI have published a manuscript in the August issue of Ecology and Evolution, which details the results of research dedicated to developing a molecular tool for distinguishing among spring and winter-spawned cod, as well as males and females, in the Gulf of Maine.

A wide-scale collaborative effort by the Atlantic Cod Stock Structure Working Group, a multidisciplinary group of scientists, has identified five biological stocks of cod in U.S. waters. The majority of these stocks can be differentiated simply by where a fish is collected; however, in the western Gulf of Maine, cod are made up of two separate stocks: spring and winter-spawned individuals that cannot be separated by any discernable external characteristics. Atlantic cod in the Gulf of Maine are currently assessed as one homogenous stock and the presence of undifferentiated spawning stocks in the region can lead to inaccuracies while estimating the abundance and production of cod.

With the help of biologists at the Massachusetts Division of Marine Fisheries and commercial fishermen, researchers at GMGI collected fin clip samples from over 200 spring and winter-spawned cod from the Gulf of Maine and used them in a sequencing project that identified over 3 million variable sites – or differences – across the genome. While the majority of those sites showed little difference between spring and winter-spawners or males and females, some regions of the genome showed strong differentiation, providing the potential to develop molecular tools with the ability to distinguish among these two crucial biological characteristics.

Using these regions as a starting point, the researchers narrowed the millions of sites down to just 25 that could reliably distinguish between spring and winter-spawned cod in the western Gulf of Maine, and a secondary set of 25 markers that could differentiate male and female cod. Applying this tool will give biologists the ability to estimate the contribution of each of these spawning groups to the Gulf of Maine and allow them to assess the spawning groups independently, rather than as one homogenous stock.

“This is an exciting tool that is now available to stock assessment biologists to further comprehend the complex genetic population structure exhibited by Gulf of Maine cod,” said GMGI Senior Research Associate, Tim O’Donnell and lead author on the publication. “Understanding stock assignment and sex information from a non-lethal fin clip sample will go a long way toward understanding the population structure and applying the best science to the cod fishery,” O’Donnell added.


Gloucester Marine Genomics Institute (GMGI) is a non-profit enterprise that addresses critical challenges facing our oceans, human health and the environment through innovative scientific research and education. By bringing world-class science and transformative workforce development to Gloucester’s historic waterfront, GMGI is catalyzing the regional economy.  Please visit www.gmgi.org and follow GMGI on Facebook, Instagram, and LinkedIn for more information.