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Seal Facts


Seals like this one photographed during the Sea Ice Physics and Ecosystem Experiment (SIPEX-II) in Antarctica, depend on sea ice to survive. They hunt for food, such as fish and krill, under the ice, and use the ice surface for rest and to have their pups. (Photo by Peter Kimball, Woods Hole Oceanographic Institution)

What are they?

  • Seals are pinnipeds, a group of animals with three separate families—phocidae (eared seals), otaridae (non-eared seals), and odobenidae (walruses)—that are the only mammals that feed in the water and breed on land.

Where do they come from?

  • Evidence suggests that pinnipeds evolved from a bear-like land animal that hunted in the water for food.

How many are there?

  • There are more than 30 species of seals worldwide.

What do they eat?

  • Seals are carnivorous and dive underwater to hunt for fish, crustaceans, seabirds, and other marine animals. Whales, sharks, and even other seals are the primary non-human predators of seals.

How deep can they dive?

  • Elephant seals are champion divers—they have been known to reach depths of almost 2,400 meters (more than 7,800 feet) and to remain submerged for 100 minutes.

How do they survive underwater?

  • Seals are protected from the cold by a thick layer of blubber; a clear membrane covers their eyes and their nostrils close and blood circulation to most of their organs is reduced while diving. They also have sensitive whiskers that help them detect prey in murky water.
  • Seals can sleep underwater and can even surface to breathe without waking.

How often do they give birth?

  • A female seal, called a cow, gives birth to one pup about once a year on land. The pups are nursed anywhere between four days and one month.
  • Most mother seals don't eat while nursing, relying instead on blubber stores for nutrition.

How often do they molt?

  • Seals molt, or shed their fur, about once a year (except their first), a process that can take as long as six weeks.

Are they in danger?

  • The Caribbean monk seal was declared extinct in 2008. Other species have been hunted to near-extinction.

Gray Seals

  • Worldwide, gray seals number about 300,000 and are found on both sides of the Atlantic in three distinct populations: Western Atlantic (150,000), Eastern Atlantic (130,000 – 140,000), and Baltic (7,500).
  • Western Atlantic gray seal bulls can reach 2.5–3.3 meters (8.2–11 feet) in length and weigh as much as 400 kilograms (880 pounds); cows are much smaller, typically 1.6–2.0 meters (5.2–6.6 feet) long and 250 kilograms (550 pounds).
  • Gray seals are gregarious animals—they gather in large groups on shore to breed, give birth, and molt.
  • Female gray seals live up to 35 years and males about 25 years.
  • Gray seals primarily hunt squid, fish, and sandeels; their main predators are humans, sharks, and orcas.
  • Gray seal pups are born in autumn (September to November) in the eastern Atlantic and in winter (January to February) in the west, and are born with white fur, which molts after two to four weeks. They nurse for two to three weeks and can quadruple in size during this time because a mother's milk is up to 50 percent fat.
  • One to four weeks after being weaned, the pups disperse and have been known to wander more than 1,000 kilometers (600 miles).
  • The mortality rate for gray seal pups is between 30 and 55 percent, largely due to fishing bycatch, entanglement in fishing gear, pollution, boat strikes, and hunting.
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News & Insights

Recognizing Massachusetts Right Whale Day

April 24 marks the first-ever Right Whale Day in Massachusetts. WHOI biologist and veterinarian Michael Moore recently met with the resident who brought this special recognition about– and explains why it’s important to raise awareness about the critically endangered North Atlantic right whale.

Critically Endangered North Atlantic Right Whales Getting Smaller, New Research Finds

A report out this week in Current Biology reveal that critically endangered North Atlantic right whales are up to three feet shorter than 40 years ago. This startling conclusion reinforces what scientists have suspected: even when entanglements do not lead directly to the death of North Atlantic right whales, they can have lasting effects on the imperiled population that may now number less than 400 animals. Further, females that are entangled while nursing produce smaller calves.

Rare Drone video shows critically endangered North Atlantic right whales

May 10, 2021


During a joint research trip on February 28 in Cape Cod Bay, Mass., WHOI whale trauma specialist Michael Moore, National Geographic photographer Brian Skerry, and scientists from New […]

Unicorns of the Arctic face a new potential threat

Narwhals and other marine mammals could be vulnerable to a new threat we’ve become all too familiar with: COVID-19

WHOI working to help save critically endangered North Atlantic right whales

North Atlantic right whales are in crisis. There are approximately 356 individuals remaining, and with over 80% bearing scars of entanglements in fishing line, the race to save this species is more critical than ever.

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News Releases

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WHOI in the News

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From Oceanus Magazine

For right whales, a dwindling food source is causing concern

As an important food source wanes in the Gulf of Maine, right whales are forced to venture further north into a minefield of ships and fishing gear

Are offshore wind farms harming whales?

WHOI whale biologist Mark Baumgartner weighs in

The value of iron for a seal

WHOI researchers travel to remote Sable Island to determine if iron gives gray seal pups a head start in life

Wind Water and Ice

Like fiction, but real. Explore the “superpowers” of three Antarctic icons

Keeping an ear out for whales

Scientists look to safeguard the mammals with robotic buoys in the New York Bight