Harbor seals are typically found in colder waters, but some have found a home along the Bay Bridge-Tunnel.
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Illustrations by Dieter Braun
It’s no secret that the Chesapeake Bay draws visitors for the rich diversity of its ecosystems, its abundant aquatic life, and its scenic attractions—including the vistas to be taken in from that 17.6-mile marvel of mid-20th century engineering, the Bay Bridge-Tunnel. But in the past couple of decades, the Bay—and the Bridge-Tunnel specifically—has offered regular seasonal sightings of a more unusual sort: harbor seals.
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These beguiling aquatic mammals are the most widely distributed of the world’s seal species; along the eastern coastline of North America, they are typically found in the colder Atlantic waters from New Jersey north into Canada. But in the Bay, and particularly along the small islands that string together the Bridge-Tunnel like so many pearls in a necklace, every winter since sometime in the early 2000s has seen a small but growing number of harbor seals settle in for the cold months.
“We usually start getting regular sightings around November or December—late fall to early winter,” says Dr. Susan Barco, senior scientist in the Virginia Aquarium’s research and conservation division. “And then they will persist here until April or May.” When they leave the Bay in the spring, they likely head north; a Navy research project that tagged harbor seals in Virginia later located the animals again along the coasts of Maine and Massachusetts.
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What’s bringing the seals here isn’t clear, but there are obvious reasons why the Bridge-Tunnel setting would appeal to them, says Barco. Harbor seals spend about half their life in the water, but the other half they spend on land in “haulouts”—places where they can rest and sun, allowing them to conserve energy. Although the seals are not particularly adept on land, in the northeast their preferred haulouts are often rocky areas that provide protection from possible predators; along Virginia’s coastlines, the Bridge-Tunnel’s erosion-protecting rock barriers offer a similar setting. There’s also the proximity to the Bay’s deep-water channel. “They are probably able to find a fair amount of food without having to swim a long distance,” says Barco. And the Bay-Bridge islands put these by-nature shy animals well away from human habitations. “It’s not a place where people and dogs are walking and the animals can be disturbed,” points out Barco.
When they are in the water, the seals are, of course, agile swimmers, with an array of remarkable physiological adaptations for their aquatic environment. They are well-insulated, with a thick layer of blubber (what human cold-water swimmers refer to enviously as “bioprene”), much of which they add in the late summer and fall. Their whiskers serve as an additional sensory system that allows them to hunt fish even in low visibility conditions by detecting their movement through the water. And although typically they hunt at shallower depths close to shore, in dives that last less than 10 minutes, the Smithsonian’s National Zoo & Conservation Biology Institute notes in its online introduction to the species that harbor seals have been recorded swimming to depths of more than 1,400 feet and can remain underwater without taking a breath for as long as 30 minutes. To achieve such feats, the seals are able to slow their heart rates to only a few beats per minute when diving.
“In the unlikely event you should encounter one in Virginia, for both the seal’s sake and your own, keep your distance.”
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Unlike some other seal species, harbor seals are also born ready to swim. To equip themselves for survival in cold water, they may as much as double their birth weight in the first month of life, nursing on their mothers’ fat-rich milk. By the time they are adults, they can reach a length of five to six feet and weigh up to 300 pounds.
Occasionally, says Barco, the seals will haul out in areas, like beaches, where there are more people, but in the unlikely event you should encounter one in Virginia, for both the seal’s sake and your own, keep your distance. Not only are they protected animals under the Marine Mammal Protection Act, but also, because they are shyer animals, “They will tend to bolt back in the water,” if approached, says Barco. “If they are constantly being harassed, that means they don’t get the rest they need.”
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And, although it should go without saying, don’t try to feed them either. Shy they may be, but they are also large, apex-predator carnivores distantly related to coyotes, wolves, and bears, “and they should be treated as such,” says Barco. And, just as important, keeping wild animals safe depends on keeping them wild. “Getting animals habituated to human contact—but particularly feeding—is a very bad idea,” says Barco. “That is one way that they get into a lot of trouble.”
This article originally appeared in the February 2021 issue.
