ORONO, Maine — Lobsters along Maine’s coast have relocated to new habitats, while the population simultaneously shrunk in abundance and grew older, according to a new study by University of Maine researchers.
For decades, most adult lobsters resided in boulder shelter habitats. UMaine says this knowledge helped inform long-term conservation efforts and regulations within the more than $740 million fishery.
However, a team of UMaine scientists found that from 1995-2021, occupancy of boulder habitats dropped 60 percent. Meanwhile, the number of lobsters residing in sediment or featureless ledge habitats, both of which have little to no geological features to use as shelters, increased 633 percent and 280 percent, respectively, according to the study.
UMaine says lobster population density across all types of habitats also declined, meaning they are fewer in number and their populations are more spread out.
According to researchers, water temperatures increased by nearly 3 degrees Celsius from 1995-2021 across these habitats, showing how lobsters and their habitats are changing with the climate.
Kelp abundance declined across lobster habitats, while diminutive algal turfs — small green mats containing multiple species of algae — increased.
Jarrett and his colleagues published their findings in the journal Marine Ecology Progress Series.
The team investigated 20 sites along Maine’s coast, from York to Jonesport. They dove 10 meters below the surface to count and measure lobster, as well as to collect data on habitat and temperature. The team also reviewed historical data for the same sites dating back to the 1990s.
While overall population density has declined, UMaine researchers say the mean size of an adult lobster was greater in 2021 than in 1996. According to the study, the increase in mean size is partially the result of fewer juvenile lobsters residing in these habitats.
While lobsters in the Gulf of Maine are now larger, the team observed that the majority, or 93 percent, were still smaller than 83 millimeters, the minimum legal size to be caught and sold, which is a promising sign for the fishery.
Lobsters are also now favoring open spaces within their habitats over rocky shelters than previously. According to researchers, the percentage of lobsters living under rocky shelters dropped 34 percent from 2000-2019, while those using no shelter at all increased 168 percent. The number of lobsters that reside underneath beds of algae have also grown 160 percent.
According to researchers, demographic shifts among Gulf of Maine lobsters — habitat, size and population density — may have resulted from a drop in baby lobsters surviving to the seafloor and less competition between individual lobsters. The lack of predators might have also influenced more lobsters to move away from boulders to more open habitats, forgoing rock shelters for cover with only algae to hide under.
