Harp seals, which normally breed on ice floes in Canada, have been sighted on Maryland beaches, possibly due to overpopulation or food shortages.
Greenpeace and other animal-rights groups campaigned against the slaughter of harp seals in the 1970s and 1980s, leading Canada to ban hunts in 1987, the Baltimore Sun reported.
"The population is growing, with an estimated 5.5 million today," said Gordon Waring, a biologist with the National Oceanic and Atmospheric Administration.
Overharvesting of cod and other North Atlantic fish might also have driven the seals south, said Jennifer Dittmer, a marine biologist with the National Aquarium.
Canada resumed seal hunting in 2000, allowing the annual harvest of 400,000 young seals with gray coats -- those slightly more mature than the white-coated pups.
Twenty-five seals have been stranded on Maryland beaches since 2000. After caring for them, the National Aquarium released them back to the Atlantic.
The animals are not attempting to breed in Maryland because they need much colder temperatures.