American lobster population and habitat preferences are changing, study finds

American lobsters along the Maine coast have moved to new habitats as the population declined in abundance and aged, according to a new study by University of Maine researchers.

For decades, the vast majority of adult lobsters resided in rock shelters. This knowledge has helped inform conservation efforts and long-standing regulations within a more than $740 million fishery.

A team of UMaine scientists, however, discovered that between 1995 and 2021, the occupancy of rocky habitats dropped by 60%. Meanwhile, the number of lobsters residing in featureless sediment or ledge habitats, both of which have few or no geological features that can serve as shelter, increased by 633% and 280%, respectively. Lobster population density in all habitat types has also declined, meaning there are fewer of them and their populations are more dispersed.

According to the researchers, water temperatures increased by almost 3 degrees Celsius between 1995 and 2021 in these habitats, showing how lobsters and their habitats are changing with the climate. The abundance of kelp has decreased in lobster habitats, while small kelp lawns – small green mats containing several species of algae – have increased.

“These differences in how lobsters use their habitats provide a context for lobster stock assessment that helps determine the health of the entire lobster population,” said Robert Jarrett, lead author of the study. study and holds a doctorate in marine biology. student.

“Some of the annual lobster surveys used in the assessment, like those from the Maine Department of Marine Resources, are limited in the types of habitats they can sample, so these habitat results help fill in some gaps information and shows that over time lobsters can change between surveys that capture them best.

Jarrett and his colleagues published their findings in the journal Advances in Marine Ecology Series. Co-authors include Damian Brady, Agatha B. Darling Professor of Oceanography; Richard Wahle, former director of the Lobster Institute, and Bob Steneck, professor emeritus of oceanography, marine biology and marine policy.

The team surveyed 20 sites along the Maine coast, from York to Jonesport. They dove 10 meters below the surface to count and measure lobsters, as well as collect habitat and temperature data. The team also looked at historical data from the same sites dating back to the 1990s.

Although overall population density has decreased, the average size of an adult lobster was larger in 2021 than in 1996. According to the study, the increase in average size is partly the result of a decrease of the number of juvenile lobsters residing in these habitats. Even though Gulf of Maine lobsters are now larger, the team observed that the majority, 93 percent, were still smaller than 83 millimeters, the minimum legal size to be caught and sold, a promising sign for the fishery.

Lobsters also now favor open spaces within their habitat rather than rock shelters. The percentage of lobsters living under rock shelters fell by 34% between 2000 and 2019, while those using no shelter increased by 168%. The number of lobsters living under beds of algae has also increased by 160%.

According to the researchers, demographic changes among Gulf of Maine lobsters (habitat, size and population density) could result from fewer baby lobsters surviving on the seafloor and less competition between individual lobsters. The lack of predators could also have caused more lobsters to move away from rocks to more open habitats, foregoing rock shelters to hide under only seaweed.

“Considering that this is one of the best-studied commercially important marine species in the world, it’s astonishing that we continue to be surprised by our iconic lobster,” Steneck said.

This study is the latest example of how UMaine students and faculty are preserving and propelling the state’s blue economy, industries that use ocean resources for economic growth without endangering the environment.

Through innovation and workforce development, the university expands understanding of the ecological and sociological changes affecting the state’s coastal communities and businesses. Its faculty and students also explore opportunities for new sectors and markets and study potential resources to mitigate the ramifications of climate change.

The UMaine Marine Aligned Research, Innovation, and Nationally-recognized Education (MARINE) Initiative enhances these efforts, which fosters collaboration and synergy among researchers, industry, government, and communities. Together, they integrate and innovate transdisciplinary marine research, education, and outreach to improve the socioeconomic well-being of Maine people and beyond.

“This study illustrates how the University of Maine is supporting Maine’s blue economy. In an evolving Gulf of Maine, sustainable management of North America’s largest fishery requires a better understanding of how lobsters use their habitat,” Brady said.