With their expressive eyes, furry appearance and natural curiosity, seals have a wide appeal. Native to polar, temperate and tropical waters on the planet, seals are also known to vocalize: a captive male harbor seal named Hoover was taught to vocalize English with a prominent New England accent.
Fast Facts: Seals and Sea Lions
- Scientific Name: Phocidae spp (seals), and Otariidae spp (fur seals and sea lions)
- Common Name(s): Seals, fur seals, sea lions
- Basic Animal Group: Mammal
- Size: Range from 4-13 feet long
- Weight: Range between 85-4,000 pounds
- Lifespan: 30 years
- Diet: Carnivore
- Habitat: Polar, temperate, and tropical seas
- Population: Unknown, but in the hundreds of millions
- Conservation Status: Tropical seals and sea lions have suffered the most from human and climatic changes. Two species are threatened; seven are currently classed as endangered.
Seals and sea lions are highly evolved for swimming, including flippers, a streamlined fusiform (tapered at both ends) shape, thick insulation in the form of fur and/or subcutaneous layer of blubber, and increased visual acuity for foraging at extremely low light levels.
Seals and sea lions are in the order Carnivora and suborder Pinnipedia, along with walruses. Seals and fur seals are related to bears, descended from an otter-like terrestrial ancestor, and they all have a more or less aquatic lifestyle.Toshi Miyamoto/Getty Images
Seals are divided into two families: the Phocidae, the earless or "true" seals (e.g., harbor or common seals), and the Otariidae, the eared seals (e.g., fur seals and sea lions).
The pinnipeds include 34 species and 48 subspecies. The largest species is the southern elephant seal, which can grow up to about 13 feet in length and more than 2 tons in weight. The smallest species is the Galapagos fur seal, which grows to up to about 4 feet long and weighs about 85 pounds.
The species have evolved to their environment, and the handful of those species which are listed as threatened or endangered are those who live in the tropics where human interference is possible. The arctic and subarctic species are mostly doing well. Two species, the Japanese sea lion (Zalophus japonicus) and Caribbean monk seal (Noemonachus tropicalis) have become extinct in recent times.
Seals are found from polar to tropical waters. The greatest diversity and abundance among seals and sea lions are found at temperate and polar latitudes. Only three phocid species-all of the monk seals-are tropical and they are all either highly endangered or, in two cases, extinct. The fur seals are also found in the tropics, but their absolute abundance is low.
The most abundant pinniped is the crabeater seal, which lives in the Antarctic pack ice; the ringed seal in the Arctic is also quite abundant, with numbers in the millions. In the U.S., the most well-known (and watched) concentrations of seals are in California and New England.
The diet of seals is varied depending on the species, but most eat primarily fish and squid. Seals find prey by detecting prey vibrations using their whiskers (vibrissae).
Seals and sea lions are mostly fish-eaters, although most of the species also eat squid, mollusks, crustaceans, marine worms, sea birds, and other seals. The ones that eat mostly fish specialize in oil-bearing species like eels, herrings, and anchovies because they swim in shoals and are easy to catch, and are good energy sources.
Crabeater seals feed almost entirely on Antarctic krill, while sea lions eat sea birds and Antarctic fur seals are fond of penguins.Image Source/Getty Images
Seals can dive deeply and for extended periods (up to 2 hours for some species) because they have a higher concentration of hemoglobin in their blood and their large amounts of myoglobin in their muscles (both hemoglobin and myoglobin are oxygen-carrying compounds). When diving or swimming, they store oxygen in their blood and muscles and dive for longer periods than humans can. Like cetaceans, they conserve oxygen when diving by restricting blood flow to only vital organs and slowing their heart rates by about 50 percent to 80 percent.
In particular, elephant seals exhibit tremendous stamina while diving for their food. Each elephant seal dive averages about 30 minutes in length, with only a couple of minutes between dives, and they have been seen maintaining that schedule for months on end. Elephant seals can dive up to 4,900 feet deep and stay down as long as two hours. One study of northern elephant seals showed that their heart rates dropped from a resting rate at the water's surface of 112 beats per minute, to 20-50 beats per minute when diving.
Pinnipeds produce a variety of sounds, both in air and water. Many of the sounds are apparently individual recognition or reproductive displays, but some have been taught to learn human phrases. The most famous is a captive male harbor seal at the New England Aquarium named "Hoover" (1971-1985). Hoover was trained to produce a variety of phrases in English, such as "Hey! Hey! Come over here!" with a noticeable New England accent. Although little is known about sound production and acoustic communications as of yet, seals, sea lions, and walruses do have some voluntary control over their sound emissions, perhaps related to their ability to adapt to diving.
In polar environments, seals restrict blood flow to their skin surface to keep from releasing internal body heat to the ice and freezing water. In warm environments, the reverse is true. Blood is sent toward the extremities, allowing heat to release into the environment and letting the seal cool its internal temperature.
Reproduction and Offspring
Because of their highly developed insulating fur-polar seals and sea lions must regulate their body temperatures between 96.8-100.4 degrees Fahrenheit (36-38 Celsius) in frigid waters-they must give birth on land or ice and remain there until the pups have built up enough insulation to withstand the cold temperatures.
In many cases, mother seals must be separated from their foraging grounds to take care of their offspring: if they can locate on ice, they can still feed and not abandon the pups, but on land, in groups called rookeries, they must limit their lactation periods so they can go without eating for a period of four or five days. Once the pups have been born, there is a postpartum estrus period, and most females are mated within a few days of the last birth. Mating takes place at the rookeries, and the males exercise extreme polygyny in these dense aggregations, with one male fertilizing many females.
In most seals and sea lions, gestation lasts just under a year. It takes between three and six years for pups to reach sexual maturity; females produce only one pup a year, and only about 75 percent survive. Female seals and sea lions live between 20 and 40 years.John Borthwick/Getty Images
Natural predators of seals include sharks, orcas (killer whale), and polar bears. Seals have long been commercially hunted for their pelts, meat, and blubber. The Caribbean monk seal was hunted to extinction, with the last record reported in 1952. Human threats to seals include pollution (e.g., oil spills, industrial pollutants, and competition for prey with humans).
Today, all pinnipeds are protected by the Marine Mammal Protection Act (MMPA) in the U.S. and there are several species protected under the Endangered Species Act (e.g., Steller sea lion, Hawaiian monk seal.) Threatened species include the Guadalupe fur seal (Arctocephalus townsendi) and the Steller sea lion (Eumetopias jubatus, near threatened). Endangered species include the Galapagos sea lion (Zalophus wollebaeki), Australian sea lion (Neophoca cinerea), New Zealand sea lion (Phocarctos hookeri) Galapagos fur seal (Arctocephalus galapagoensis); Caspian Seal (Pusa caspica), Mediterranean monk seal (Monachus monachus), and Hawaiian monk seal (M. schauinslandi).
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