9 Fascinating Facts About Seals

Seals, also known as pinnipeds, make up three diverse groups of semi-aquatic carnivorous marine mammals. Constituting the most species-rich clade of living marine mammals, there are 33 types of seals widely distributed around the world, dating back to the late Oligocene (27-25 million years ago) period according to fossil records, with more than 50 species existing at one point in time.

The three subclades of pinniped include Phocidae, or true seals, Otariidae, or fur seals and sea lions, and Odobenidae, with only one remaining species, the walrus. The earliest pinnipeds were aquatic carnivores with well-developed, paddle-shaped limbs and feet, and likely went through a freshwater-dwelling phase during their transition from land-living to spending the bulk of their time in the ocean. Read on to learn more about these adorable marine animals.

1. Seals Are Related to Bears, Skunks, and Badgers

Evolutionary biologists have been arguing over seals' origins for more than a century. While relatively sure that pinnipeds evolved from land-dwelling carnivores, scientists are divided on the precise steps that occurred between terrestrial ancestors and modern marine mammals. Along with the three subclades of pinniped, the suborder Caniformia contains Ursidae (bears), Mustelidae (badgers, otters, weasels, and relatives), and Mephitidae (skunks and stink badgers). In 2007, a nearly complete skeleton of a new semi-aquatic carnivore from an early Miocene lake deposit in Nunavut, Canada, was discovered and became known as an evolutionary link between land mammals and seals.

2. "Earless" True Seals Actually Do Have Ears

Seals' ability to hear can vary between species. "Earless" seals lack an external ear flap, present on fur seals and sea lions, but they still have ears present beneath the surface of the skin. True seals (phocids) hear higher frequencies under water than otariids (fur seals and sea lions), and the opposite is true for airborne sounds. All pinnipeds are more sensitive to underwater sounds than they are to airborne sounds.

3. The Largest Seal Weighs More Than Four Tons

A male southern elephant seal has an average weight of 8,000 pounds while females are much smaller. This drastically contrasts the smallest seal in the family of otariids, the Galapagos fur seal, which ranges between 60 to 140 pounds on average. Almost all seals, with the exception of the nearly-hairless walrus, are covered in thick fur, and have layers of fat to keep them warm called blubber.

4. Mothers and Pups Bond With a Unique Call

Researchers performed vocalization playback experiments on 18 breeding female harbor seals to assess their abilities to recognize calls of their pup and to evaluate the effect of maternal protectiveness. They found that mothers were more responsive to the calls of their own pup than to non-filial pups after only three days. Mother seals' responses also varied depending on their protective behavior displayed towards their pup. And species of seals in which the young are more mobile and the colonies are more dense are more likely to strongly develop vocal recognition abilities.

5. They Have "Smokers' Blood" To Help Survive Deep Dives

Both seals and heavy human smokers have high levels of carbon monoxide in their blood streams. While humans acquire it from burning tobacco, researchers think seals' blood carbon monoxide levels are connected to their deep dives. One study found that elephant seals' blood is around 10% carbon monoxide, which researchers attribute to the animals holding their breaths for about 75% of their lives. Exhaling is the only way for an animal to clear carbon monoxide from its body.

6. The Baikal Seal Is the World's Only Freshwater Pinniped

One of the smallest true seals, the Baikal represents the seal's evolutionary journey from terrestrial to semi-aquatic, when seals likely spent time in freshwater before making their transition from land to oceans. Lake Baikal, a freshwater lake in Siberia is home to a whole host of interesting creatures, and is both the oldest, and deepest, lake on the planet.

7. Their Brain Temperature Drops When They Dive

Research on hooded seals illustrated a drop in brain temperature by 3 degrees Celsius over the course of a fifteen minute dive, in a process designed to reduce oxygen consumption by the brain. The seals circulated cold blood to the brain through the large superficial veins from their front flippers, ultimately reducing the brain's oxygen demand by an estimated 15-20%. This extends a seal's diving capacity substantially, and provides additional protection against hypoxic injury.

8. They Can Eat A Lot of Seafood

Because seals are typically found along coastlines, they primarily consume fish, squid, and shrimp, as well as other crustaceans, mollusks, and zooplankton organisms. Researchers theorize that their terrestrial ancestors were insectivores. Larger seals can eat 10 pounds of food per day. As some populations have increased in recent decades, researchers are carefully studying the impact on seal's prey, including salmon, and encouraging management practices that protect both seals and potentially threatened fisheries.

9. Climate Change Is Their Newest Threat

In the last century, both the Japanese sea lion and the Caribbean monk seal have become extinct, the latter considered a harbinger of human-caused extinction in coral reef systems. Historically, seals have faced threats from hunting, accidental trapping, marine pollution, and conflicts with local people. More recently, seals face a new threat in the form of habitat loss as a result of climate change. Arctic-dwelling bearded and ringed seals are listed as threatened under the Endangered Species Act because their sea-ice habitat is melting. Advocacy groups are working to envision shifting habitats for these animals as the climate changes.