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North American seals are recovering in some places, but there is no single trend shared by every species or population. Many harbor seal populations grew after bounty hunting ended and federal protections took effect, while current trends vary by stock; gray seals have returned to historic U.S. pupping sites, in part through immigration from Canada. Here are 10 remarkable seal facts, with the population numbers kept in their proper context.
What does “seal populations are rebounding” really mean?
It means recovery in particular species, places, and time periods—not a uniform increase across North America. For harbor seals in U.S. waters, NOAA Fisheries reports that West Coast stocks have fluctuated without an obvious overall trend or grown, New England appears stable, and some Alaska stocks likely declined during 2011–2018. Those differences matter: one stock’s recovery cannot stand in for every seal population.
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Gray seals illustrate another kind of recovery. After being absent from some historic U.S. pupping areas, they recolonized sites in the Northeast. Population growth contributed, but so did immigration from Canadian colonies, according to a 2020 Journal of Mammalogy study. Pup counts at four data-rich U.S. sites had estimated annual changes ranging from −0.2% (95% confidence interval: −2.3–1.9%) to 26.3% (95% confidence interval: 21.6–31.4%). The study’s periods varied by site and ran from 1988 to 2019; those figures describe observed pup-count trends at the selected sites, not the annual growth rate of the entire gray seal population.
For a range-wide reference, NOAA’s 2024 assessment gives a best estimate of 394,311 gray seals in the western North Atlantic in 2021: 366,400 in Canada and 27,911 in U.S. waters. This is a dated, model-based estimate for one stock, not a current census of every seal in North America. NOAA’s species summary gives a rougher figure of about 450,000 in Canadian and U.S. waters; because the summary and assessment use different estimates, they should not be merged into a single number. The U.S. total is especially uncertain: the assessment estimated it using a Canadian pup-to-total-population ratio.
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What are 10 incredible facts about seals?
- Harbor seals have no external ear flaps. Look closely at either side of the head and there is a small opening to the ear canal, rather than a visible, projecting ear. Harbor and gray seals are “true seals,” a group distinguished in the available data by this lack of external ear flaps. It is one reason a seal’s head can look smooth and streamlined.
- Some harbor seals live far from the ocean. A small harbor seal population lives in Alaska’s Iliamna Lake, a freshwater lake far from the sea. Harbor seals are found along both North America’s Atlantic and Pacific coasts, and they also occur in rivers and freshwater lakes. This unusual inland population is a reminder that a species’ range can include habitats beyond the coastal scenes people most often associate with it.
- Harbor seal pups can swim on the day they are born. NOAA Fisheries puts it plainly: “Harbor seal pups can swim at birth.” Their early swimming ability does not mean they are independent; harbor seals also use haul-out sites for giving birth and nursing. A pup on shore is not automatically abandoned or in need of human help.
- Very young harbor seals can already dive. NOAA says pups can dive for up to two minutes when they are two to three days old. That is a specific early-life capability, not a measure of how long an adult can stay underwater. Harbor and gray seals differ in size, range, and other traits, so a number for one species should not be generalized to all seals.
- A “haul-out” is more than a place to nap. Harbor seals come out of the water on rocks, reefs, beaches, and drifting glacial ice. These sites support resting, temperature regulation, molting, social interaction, birth, and nursing. Their use changes with circumstance, so seals gathered on land may be carrying out several different parts of their life cycle—not simply basking.
- Harbor seals move differently on land than sea lions. Their fused pelvic bones prevent them from bringing their hind flippers beneath the pelvis to walk in the sea-lion manner. NOAA describes their land movement as caterpillar-like: they flex their bodies and push along, rather than walking upright on their hind flippers. This anatomy helps explain why a seal that looks sleek in water can seem awkward on shore.
- Adult male gray seals have a distinctive “horsehead” look. Males develop especially large heads and long, curved noses; NOAA says that appearance explains the common nickname “horseheads.” Gray seals occur along North Atlantic coasts, and their longer, curved profile contrasts with the short, dog-like snout of a harbor seal. Head shape is a useful clue, though distance, angle, and age can make identification uncertain.
- Gray seal pups begin life in a white coat. They are born with white fur called lanugo and shed it at about three weeks old. That soft newborn coat is not the adult gray seal’s typical appearance, so a white pup and a gray adult can look surprisingly unlike one another. In the western North Atlantic, gray seal pupping takes place from December through February.
- Gray seals can dive to 1,560 feet. NOAA reports that they can dive to that depth and remain submerged for as long as an hour. These are the capabilities NOAA gives for gray seals; they should not be treated as a guaranteed performance for every individual or as a claim about harbor seals. Such underwater time also helps explain why shoreline sightings reveal only part of a seal’s life.
- Gray seals eat a varied, changing diet. Their food includes fish, crustaceans, squid, octopuses, and sometimes seabirds. The mix varies with age, sex, season, and location, so there is no single menu that describes every gray seal. A local observation of one prey item cannot establish what the species eats everywhere.
How can you tell a harbor seal from a gray seal?
Start with the head, then consider body size and context. Harbor seals have a short, dog-like snout; gray seals have a longer, curved nose, particularly pronounced in adult males. A young gray seal may be in its white lanugo, unlike the familiar adult appearance.
Size can help, but the figures are species descriptions, not a promise about any one animal. NOAA lists harbor seals at up to 6 feet and 285 pounds. Adult female gray seals average about 7.5 feet and 550 pounds; males may reach 10 feet and 880 pounds. The Atlantic and Pacific coastal range of harbor seals also differs from the gray seal’s North Atlantic distribution. Because these are wild animals and identification may be uncertain at a distance, do not approach for a closer look.
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How do scientists estimate seal populations?
Researchers use methods designed for a population that spends much of its life underwater and gathers at shore only at certain times. NOAA describes aerial photography of haul-out sites as one way to survey abundance. A photograph or beach count is a snapshot of seals visible at a location; it is not by itself a full population estimate.
Estimates also depend on what can be observed and how researchers account for what cannot. In NOAA’s 2024 western North Atlantic gray seal assessment, the U.S. total was estimated from pup counts using a Canadian pup-to-total-population ratio. That modeling choice, along with other uncertainties, is why the assessment’s dated estimate should be read as a best estimate rather than an exact census. It is also why a broad summary figure and a formal stock-assessment estimate may differ without proving that the population rose or fell between the two numbers.
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Diet research uses different evidence. NOAA researchers may examine scat, stomach contents, fatty acids in blubber, and DNA in stomach contents. Those sources can help reveal prey that a casual observer would never see a seal catch. They also help researchers account for variation by season, location, sex, and age rather than treating one sighting as a complete picture.
How should you watch seals safely?
Watch from a respectful distance, never feed a seal, and follow local wildlife guidance. Feeding is harmful and illegal, according to NOAA’s gray seal guidance, and it can alter seal behavior. A seal resting on a beach or rock may be using an important haul-out, nursing, or recovering between trips in the water.
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Harbor seals, like all marine mammals, are protected under the Marine Mammal Protection Act. If a seal’s condition or behavior concerns you, do not try to touch, move, or feed it; use local wildlife guidance rather than intervening on your own. Keeping people and pets back also reduces disturbance to the animal and the rest of a haul-out group.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why these facts need species and place attached
“Seal” covers animals with different bodies, pup traits, ranges, and population histories. Harbor seal pups can swim at birth; gray seal pups are born in white lanugo. Harbor seal stocks do not all show the same recent trend, while the gray seal’s return to some northeastern U.S. pupping sites includes both population growth and movement from Canada. When a number or behavior is reported, check which species it describes, where the observation was made, and what period it covers.
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For readers who want to identify local marine mammals without getting close, Alaska Sea Grant lists regional marine mammal guides, including an Atlantic and Gulf of Mexico guide and a separate Alaska guide. Choose the edition that matches the coast; a regional field guide is more useful than assuming one book covers every seal likely to be seen.
Frequently Asked Questions
Are the harbor seals in Iliamna Lake a separate species?
The population described by NOAA is a small population of harbor seals, not a separate seal species. Its inland freshwater location is unusual, but it remains part of the harbor seal story.
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When are gray seal pups born in the western North Atlantic?
The pupping season falls from December through February. A white-coated pup seen during that period may be wearing its normal newborn lanugo, which it sheds at about three weeks.
What evidence do researchers use to learn what seals eat?
NOAA describes research using scat, stomach contents, blubber fatty acids, and DNA found in stomach contents. These methods reveal diet evidence beyond the prey people might happen to see near shore.
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