Each summer, nine million pounds of walrus flesh packs the beaches of Round Island, off the southwest coast of Alaska in the Bering Sea. Scientists aren't exactly sure why, but for a few months each summer, about 12,000 male Pacific walruses congregate on the two mile (3.2 km) long island. From the base of the cliffs to the bubbly surf, all you can see is walrus.
Known as rather gregarious creatures, the walruses may simply enjoy one another's company -- although they do occasionally jab a neighbor with their long tusks to assert dominance. Or, perhaps they are simply trying to stay warm. After all, temperatures can slip below zero degrees Fahrenheit (-32 degrees Celsius). Or maybe they're just chatting about the ladies; the female walruses are far away, in route back from their yearly migration north -- with calves in tow.
Whatever the reason for this months-long male bonding, it presents an ideal setting for scientists to study the mammal, whose name in Danish means "sea horse" or "sea cow." In the years since research began, biologists have learned much about this hardy creature of the arctic. For example, in just the last decade, scientists discovered that the walrus doesn't use its tusks to dig for food along the ocean bottom, as previously thought. It actually blows a stream of water at the sea floor to stir up the prey.
On the following pages, you'll learn even more about this tusked animal -- from how the walrus removes clams from shells (think vacuum cleaner) to how deep it can dive (hint: almost the full length of a football field) [source: Lanken].
Walrus Classification and Body Plan
Walruses are the second largest animal belonging to the order Pinnepedia, which also includes seals and sea lions. Of these animals, only the elephant seal can grow larger than the walrus. Walruses are also the only member of the order to possess tusks -- two especially long upper canines that can reach lengths of 3 feet (0.91 meters) and weigh 12 pounds (5.4 kg). In fact, the walrus's family name, Obodenidae, means tooth-walker in Greek, referring to the way walruses pull themselves up out of the water by hooking their long tusks into the ice.
You might assume walruses use their tusks as weapons, but primarily they use their tusks as tools and for establishing dominance. When males do get feisty, the especially thick skin around their neck and shoulders protects them from sharp jabs. In addition to using their tusks to haul themselves out of the water, walruses also use them when underwater to break breathing holes in the ice. And they may even hook the tusks over the ice like clothes hangers in order to take a break from swimming. Both the males and females have tusks, but the males' are longer, straighter and stronger, and may continue to grow for up to 15 years [source: Burns].
Walruses are generally a darkish brown color and have large, round bodies. They appear relatively clumsy on land but move easily through the water, where they spend two-thirds of their lives. Walruses have four flippers with rough bottoms to help provide traction on the slippery snow and ice. To move on land, they turn their two front flippers at 90-degree angles to their body and flap their two rear flippers directly underneath their pelvis. In the water, they can reach speeds up to 21.7 mph (35 kph). A walrus's front flippers are used for steering and its two hind flippers alternate strokes to propel the walrus through the water at an average of 4.3 mph (7 kph) [source: Burns].
The two walrus subspecies -- the Atlantic walrus and the Pacific walrus -- are geographically and reproductively isolated, meaning they do not interbreed or interact in any way. The two subspecies are similar except for size.
- Male Pacific walruses usually grow to between 9 and 12 feet (2.7-3.6 m) and weigh between 1,764 pounds and 3,748 pounds (800-1700 kg). Females grow to lengths between 7.5 feet and 10 feet (2.3-3.1 m) and weigh between 400 pounds and 1,250 pounds (882kg-2756 kg).
- The Atlantic males are a bit smaller at 9.5 feet (2.9 m) and 2,000 pounds (908 kg). Females are shorter but fatter at about eight feet (2.4 m) and 1,750 pounds (794 kg) [source: Burns].
Walruses are located throughout the arctic region. The Pacific walrus is found in the Bering, Chuckchi and Laptev seas of the Pacific Ocean. The Atlantic is found in the Atlantic Ocean primarily along the northeast coasts of Canada and in Greenland. Roughly 250,000 walruses exist today; 200,000 of these are Pacific stock [source: Burns]. As you might expect, more is known about the more prevalent Pacific walrus. This is partly due to funding issues, but also because of sheer numbers.
On the next page, you'll learn how a walrus's mustache can supplement its eyes and why its feeding habits might make it a good contender in a competitive eating contest.
Walrus Sensory Organs and Eating
Walruses do an excellent job of locating and consuming prey, but it's not because of good eyesight. The walrus's two eyes, on the front (not the sides) of its round head, don't provide especially good vision. Instead, other senses do the bulk of the work. A walrus's ears -- two small openings with protective flaps -- can detect noises up to a mile (1.6 km) away. Walrus noses are sensitive enough to detect the approach of predators and to identify young. In addition, a walrus possesses anywhere from 400 to 700 whiskers in 13 to 15 rows around the nose. The whiskers, also known as vibrissae, are attached to muscles and are supplied with blood and nerves, which makes them highly sensitive.
Walruses use these sensitive whiskers to locate prey. They hunt with their noses to the sea floor, squirting water out of their nostrils to stir up burrowing prey. Walruses generally forage in groups at depths between 33 feet and 164 feet (10 m-50 m) and seem to prefer clams as a food source. Walruses are not picky, though. They'll eat pretty much any bottom dweller including worms, snails, crabs and sea cucumbers. When a walrus does locate some shelled prey, it uses its mouth as a vacuum to suck the animal right out of the shell. The suction is so powerful that walruses in captivity have sucked holes in plywood and stripped paint from walls [source: Vlessides]. Walruses do not chew their food, but simply swallow it whole. A grown walrus can consume 3,000-6,000 clams in one sitting. In fact, walruses consume approximately 4.2 percent to 6.2 percent of their body weight each day [source: Burns].
So how do walruses eat underwater for so long without air? And how do they tolerate frigid water temperatures? Keep reading to learn how walruses have adapted to endure the harsh climate.
Walrus Environmental Adaptations
Walruses live in one of the harshest environments on Earth. Not only do they dwell where temperatures are frigid -- they also spend the majority of their time in the water, where they lose body heat 27 times faster than they do on land. Yet the walrus manages to maintain a core body temperature of 97.9 degrees Fahrenheit (36.6 degrees Celsius). Walrus skin generally stays one to three degrees warmer than the water, and the animal's metabolism is not affected at temperatures between -4 degrees and 59 degrees Fahrenheit (-20 degrees Celsius to 15 degrees Celsius). Some walruses have even been observed unaffected by water temperatures as low as -31 degrees Fahrenheit (-35 degrees Celsius) [source: Burns].
So, how do they do it? With good insulation; walruses have a thick layer of body fat just under their skin that keeps them warm, streamlines their form and provides them with energy when reserves dip low. This blubber layer can be up to 3.9 inches (10 cm) thick and may comprise up to a third of the animal's body mass in the winter [source: Burns]. The walrus's blood vessels also constrict and move blood away from skin and toward chief organs, where heat won't escape. When the temperature is cold or a walrus has been underwater for a long time, its skin appears white for just this reason. When a walrus is warm, its skin takes on a pinkish hue as the blood vessels dilate and blood returns to the skin's surface to let heat escape. Walruses do have hair, which they gradually shed and replace over the summer months. But this hair is only 0.3 to 0.5 inches (7mm-12mm) long and plays little, if any, role in keeping the animals warm.
On top of being good at tolerating the cold, walruses have acquired several adaptations that enable them to go long periods without oxygen. This ability is connected with their circulation. When they dive, their heart rate slows and blood travels to the organs that need the most oxygen. In addition, walruses have a high level of a protein called myoglobin in their blood. Myoglobin binds to oxygen, carries it through the walrus's body and stores it in the muscles. Also, pharyngeal muscles in the walrus's throat close up when they dive to prevent water from entering the animal's lungs.
To learn more about walrus behavior and to find out how a male walrus wins over its mates with a sonorous serenade, go to the next page.
Walrus Behavior and Reproduction
Walruses have few predators other than the occasional killer whale or brave polar bear. Thus they tend to live relatively long life spans of around 30 years. During their lifetimes, male and female walruses live apart, in separate herds. Females stay with the same herd throughout their lives, and males leave their birth herd after two to three years to join the male herd.
Female Pacific walruses migrate annually in herds. In summer when the ice melts and recedes, the females head north to the Chuckchi Sea. They return south to the Bering Sea before the ice freezes in the winter. Researchers aren't entirely sure why males don't migrate to the extent that females do, but some scientists speculate it may be related to sperm production. Little is known about the migration patterns of the Atlantic walrus; they seem to stay in the same general area year-round.
Male walruses usually reach sexual maturity at around age eight to 10. Females mature at five to six years old. Even though they are sexually mature, males do not usually mate until around age 15, and females don't begin mating until age 10.
Pacific walruses mate between December and March. The females meet the males to mate when they return from their migration north. Females only mate once every two years or more due to their long gestation period of 15 months. Thus, females who are still pregnant from the previous breeding season separate from the others when the mating ritual begins.
The remaining females congregate on the ice pack and prepare to be entertained by the males in the water. One or two males generally perform for each congregation of roughly 23 females -- presenting a series of vocalizations both above and below water. Here, the males' pharyngeal muscles (near the throat) come in handy both as flotation devices and as amplifiers. The males simply inflate the pouches to remain upright in the water and begin to serenade. Along with other noises, they clack their teeth, whistle and make bell sounds until a female is so impressed that she enters the water to mate. Males usually space themselves 23 feet and 33 feet (7-10 meters) apart or battle for the prime display spot. Dominance in the male herds is established by body size, tusk size and aggressiveness.
For the first four or five months of gestation, fertilized eggs float around in the female's uterus before implanting in the uterine wall and starting to develop. This delay in implantation is determined by metabolic conditions, and is thought to ensure that calves are born in the optimal environment. Females give birth between mid-April and mid-June, as they migrate north. They stay with their newborns until the following April just before their next birth. If they don't get pregnant with a new calf the following season, they may stay with their young for as long as two and a half years.
Cows are very protective of their young. They even go so far as to separate them from the other walruses to form nursery herds with other mothers. Cows nurse their calves for up to two years depending on whether they get pregnant again the following year. Cows often give their young rides on their backs even though calves can usually swim after just one month.
Walrus calves are certainly not tiny little bundles at birth. They weigh between 99 pounds and 165 pounds (45 kg-75 kg) when born and grow 4 to 6 inches (10-15 centimeters) a month, gaining 1.5 pounds to 2 pounds (0.7 kg-0.9 kg) a day. They tend to be darker than the adults in color, and they get lighter as they age.
Walruses seem harmless enough. So why have hunters killed so many walruses that their overall numbers have periodically dwindled? Learn more on the next page.
Walrus: History, Protection and Tradition
Though walruses have few natural predators, man has hunted them since the ninth century. Hunters have stalked them for their oil, ivory and skin. Because of this, walrus populations have dropped to extremely low levels and then recovered at several points in human history.
Walrus oil -- created by boiling walrus blubber at high temperatures -- was greedily sought for lamps, soap and as a machine lubricant between 1860 and 1880. During that period, approximately 10,000 walruses were killed a year in the eastern Arctic alone [source: Lanken]. After the most recent depletion, however, walrus hunting has largely been restricted in Canada, Russia and the U.S. Only native populations who rely on the walrus as a source of food are permitted to hunt the animal.
In the United States, the Marine Mammal Protection Act of 1972 not only protects the walrus from hunters but also prohibits the trade of walrus ivory. Only ivory that predates the law or has been carved by an Alaska native can be legally traded [source: Burns]. In addition, although the walrus is not endangered, it is listed under Article III of CITES, the Convention on International Trade in Endangered Species. This status gives it some protection by placing restrictions on the global trade of walruses and walrus products.
After significant fluctuations in walrus populations over the last several hundred years, current populations appear to be stable and may even be thriving. Although some illegal ivory trade is inevitable and the effects of global warming remain to be seen, walruses are enjoying a welcome stability in their total numbers.
For more information and some interesting videos of walruses, don't miss the links on the following page.
From ears to fur, seals and sea lions may be related, but they certainly aren't the same. Prove your knowledge on these cousins at HowStuffWorks.
Related HowStuffWorks Articles
More Great Links
- Burns, John J. "Walrus." Alaska Department of Fish and Game. 1994. http://www.adfg.state.ak.us/pubs/notebook/marine/walrus.php
- Lanken, Dane. "Grace under water: A thick-skinned beast reveals its inner beauty." Canadian Geographic. 122.2 (March 2002): 48 (6). (Feb. 2, 2008)http://find.galegroup.com/ips/start.do?prodId=IPS
- Mathews, Richard. "The summer-long bachelor party on Round Island." Smithsonian. 14 (Oct. 1983): 68 (6) (Feb. 2, 2008)http://find.galegroup.com/ips/start.do?prodId=IPS.
- Murdoch, William J. "Principles of Mammalian Production." University of Wyoming.http://www.uwyo.edu/wjm/Repro/implant.htm
- Rhett A. Butler. "Global warming could doom the walrus." April 14, 2006.http://news.mongabay.com/2006/0413-walrus.html
- Robichaud, Heidi. "Laws and regulations governing the sale of ivory."http://gustavus.com/heidi/laws.html
- National Park Service. "Subsistence and Walrus Hunting."http://www.nps.gov/akso/ParkWise/Students/ReferenceLibrary/BELA/SubsistenceWalrusHunting.htm
- Vlessides, Michael. "In Search of the Tooth Walker -- In the frigid Arctic, researchers attempt to assemble the puzzle that is the Atlantic walrus." International Wildlife. (Nov-Dec 2000) (Feb. 2, 2008)http://find.galegroup.com/ips/start.do?prodId=IPS.
- "Walrus." SeaWorld/Busch Gardens Animal Information Databasehttp://www.seaworld.org/infobooks/Walrus/home.html