A recent study conducted by researchers from the University of Maine reveals that American lobsters along Maine’s coastline have shifted to new habitats, experiencing both a decrease in population and an increase in age.
Traditionally, most adult lobsters lived in boulder shelter habitats, which informed conservation strategies and regulations in Maine’s $740 million lobster industry.
However, the UMaine research team discovered that between 1995 and 2021, the occupancy of boulder habitats plummeted by 60%. In contrast, lobsters found in sediment or featureless ledge areas—environments lacking distinct geological features—rose dramatically by 633% and 280%, respectively. Overall, lobster population density across all habitats decreased, indicating a decline in numbers and a broader dispersion of the remaining lobsters.
According to the researchers, the water temperatures in these areas have increased nearly 3 degrees Celsius since 1995, signaling how climate change is affecting lobsters and their environments. Kelp has become less abundant in lobster habitats, while small green algae mats—each composed of various algae species—have seen a rise in numbers.
Robert Jarrett, the lead author of the study and a marine biology Ph.D. candidate, stated, “These changes in how lobsters inhabit their environments provide essential context for stock assessments that gauge the overall health of the lobster population.” He noted that certain annual surveys employed in these assessments, like those from the Maine Department of Marine Resources, have limitations in the types of habitats they can sample. Therefore, the new habitat insights help address existing knowledge gaps and indicate that lobsters may be increasingly shifting to areas where they are better captured in surveys.
The findings were published in the journal Marine Ecology Progress Series, with contributions from co-authors 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 research team explored 20 different locations along Maine’s coast—from York to Jonesport—diving down 10 meters to count, measure lobsters, and collect habitat and temperature data. They also examined historical data from the same sites going back to the 1990s.
Despite an overall decline in population density, the average size of adult lobsters was larger in 2021 compared to 1996. This increase is partly due to a reduced number of juvenile lobsters in these habitats. Although lobsters in the Gulf of Maine are generally larger, the majority—93%—still remain under the legal catch size of 83 millimeters, which is a promising indicator for the fishery.
Interestingly, lobsters are now preferring open areas in their habitats instead of rocky shelters as they did before. From 2000 to 2019, the percentage of lobsters living under rocky shelters dropped by 34%, while those without any shelter rose by 168%. Additionally, more lobsters are taking refuge under algae beds, which increased by 160%.
The researchers noted that these demographic shifts in Gulf of Maine lobsters—regarding habitat, size, and population density—could be attributed to fewer baby lobsters successfully reaching the seafloor and reduced competition among individual lobsters. The low presence of predators may have further encouraged lobsters to abandon boulder shelters in favor of more open spaces with only algae for cover.
Bob Steneck remarked, “Given that this species is one of the best studied commercially important marine creatures globally, it’s remarkable how often we continue to be surprised by our iconic lobster.”
