NORTHERN ELEPHANT SEALS
The northern elephant seal (Scientific name: Mirounga angustirostris) is the largest of the “true” seal in the Northern Hemisphere. Adult males use their large, inflatable noses during the winter breeding season to resonate sound when vocally threatening each other. The largest colonies of northern elephant seals are found off southern California in the Channel Islands. They have one of the longest migrations of any mammal, some have been recorded traveling over 20,000 kilometers (13,000 miles roundtrip). [Source: NOAA]
Northern elephant seals were once thought to be extinct due to commercial sealing in the 1800s. Populations of northern elephant seals in the U.S. and Mexico were all originally derived from a few hundred individuals surviving in Mexico. Its population began to steadily increase in the early 1900s. Now there are around 110,000 of them.
Northern elephant seals are known for diving very deep for long periods of time. One reason they do this is to avoid predators, namely sharks and orcas, which tend to hang out near the surface. Some also migrate to the open ocean to avoid predators that stick closer to the shores. They are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them) and homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings)
There is a notable difference in lifespan between males and females. Females generally live for about 19 years, while males only live for about 13 years. Ascertaining lifespans of these animals has long been difficult. One way it was done was by estimating of survival of reproductive females represented in percentages with the probability of survival decreasing with each year of life. In the first year of life, a female's chances of survival are 35 percent, at two years, 30 percent, and at three years, 20 percent. [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures
Northern Elephant Seal Habitat and Where They Are Found
Northern elephant seals are found in the eastern and central North Pacific Ocean. Though they range as far north as Alaska and as far south as Mexico, they typically breed in the Channel Islands of California or Baja California in Mexico. Northern elephant seals breed and give birth in California and Baja California, primarily on offshore islands from December to March. Males feed near the eastern Aleutian Islands and in the Gulf of Alaska, and females feed further south, in the offshore waters of Washington and Oregon. Adults return to land between March and August to molt, with males returning later than females. Adults return to their feeding areas again between the spring/summer molt and the winter breeding season. [Source: NOAA]
When Northern elephant seals are on land they typically aggregate in large groups on sandy, rocky or muddy coastline shores, particularly on offshore islands. They spend only 10 percent of their time on land, during reproduction and moulting. [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
The other 90 percent is spent in the sea, diving and foraging for food. Only 11 percent of this time in the water is spent at the surface. This means that an extraordinary 85-90 percent of their time at sea is spent under water, often in very deep water at great depths. These mammals regularly dive to depths of over 500 and have gone as deep as 1500 meters for extended periods of time — 20 to 70 minutes.
Males travel north, remain closer to land, and tend to return to the same locations to feed year after year. Females migrate away from the land, west to the open ocean, and are less accurate in returning to the same places each year.
Northern Elephant Seal Physical Characteristics
Northern elephant seal range in length from 3 to 5 meters (10 to 16.4 feet) and range in weight from 600 to 2300 kilograms (1320 to 5066. pounds). Sexual dimorphism (differences between males and females) is very pronounced. Males are larger than females. Males and females have different shapes and their ornamentation is different. Males reach 4 meters (13 feet) long and weigh up to 2,000 kilograms (4,500 pounds). Females reach 3 meters (10 feet) in length and weigh 590 kilograms (1,300 pounds). [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
Adults northern elephant seals are dark brown or gray. Males are usually a darker brown, while females are a light tan color. Hair is reduced on adult males and females and is completely absent for a short time after moulting. Pups are black until they are weaned at about 6 weeks old and they molt and turn light silver. Countershading is a feature to all adults and newly weaned youngsters, with a darker color on the back and a lighter color on the bottom.
When males reach puberty at about 7 years old, they develop a large inflatable nose, or "proboscis." The proboscis overhangs their lower lip by about 8 inches. The proboscis is absent in females and larger than the ones of southern elephant seals. Young males begin development of the proboscis at two years of age, but it is not fully developed until years later. These animal also develop a robust, thick neck that is heavily creased and lighter in color than their dark bodies. Conversely, females maintain their smaller noses and smooth necks. Northern elephant seals possess two, lobed hind flippers. Pinnae (external ears) are absent, giving the ear the appearance of being flush with the skin. Teeth are dimorphic in the sexes with males having considerably enlarged canines that are used in fighting.
Northern Elephant Seal Behavior
Northern elephant seals are diurnal (active during the daytime), nocturnal (active at night), motile (move around as opposed to being stationary), migratory (make seasonal movements between regions, such as between breeding and wintering grounds), solitary, territorial (defend an area within the home range), colonial (living together in groups or in close proximity to each other), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
Northern elephant seals spend much of the year — generally about nine months — in the ocean. They are usually underwater, diving to depths of about 300 to 750 meters (1,000 to 2,500 feet) for 20 to 30 minute intervals with only short breaks at the surface. They are rarely seen out at sea for this reason. While on land, they prefer sandy beaches. They fast during mating season and can lose up to 36 percent of their body weight during this time. When molting occurs, they shed their short, dense fur along with large patches of old skin. Molting takes 4 to 5 weeks to complete. [Source: NOAA]
Northern elephant seals are probably solitary when out at sea. They are social when they come ashore. They are on the move much of their lives, migrating while foraging for food. A social hierarchy with males often fighting one another during mating season, but the males are less aggressive toward each other when they haul out to moult.
According to Animal Diversity Web: One of the most extraordinary features to these animals is their dive behavior during foraging migrations. The extended period of time in which these animals stay under water is not brought about by their ability to hold their breath. Air is dispelled from the lungs before these seals dive, and throughout the 20 to 70 minutes the animal is under water, the oxygen they require is obtained from their blood and tissues. Northern elephant seals possess blood that is rich with hemoglobin and tissues rich in myoglobin, thus increasing their oxygen storing abilities. Another feature of this diving behavior that has perplexed researchers is the lack of rest or sleep for such an extended period of time. Recordings have indicated that these animals conduct dive after dive, 24 hours a day, sometimes for months at a time. It is thought that the dive activity may be a form of sleeping for the seals because their metabolic rate is very low. [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
Northern Elephant Seal Food and Eating Behavior
Northern elephant seals feed of mostly squid and fishes, but also rays and sharks. According to Animal Diversity Web: Northern elephant seals spend 90 percent of their lives in the water in order to feed. During their foraging migrations, they dive into the water repeatedly and continuously to find food, never stopping to rest or sleep for months at a time. Females and males feed separately from each other. [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
Male foraging behavior is characterized by benthic (bottom-dwelling) dives to the sea floor. By contrast, females exhibit pelagic (open ocean) diving while foraging which is defined by a trip to the floor, a partial ascent, another trip to the floor, a partial ascent, etc. There is some speculation as to the reason why male size is so extreme in relation to female size and some suggestions indicate that food type may be a contributing factor. Males are more likely to eat food sources that are dense in mass such as sharks and skates, while females eat foods that are less dense such as squid. These differences in foods is a likely occurence to the different locales in which they are foraging. This resource partitioning is likely to be the result of differences in body size. Males are less vulnerable to predators and are thus safer foraging in areas with more predators. Females are more vulnerable to predators and thus must forage in areas with fewer predators.
While elephant seals are on land they are fasting. They go for extended periods of time without food while they are reproducing and moulting. During this time, all nutrition and energy is broken down from fat that is stored on their bodies as blubber. It is believed that these animals never drink water. Their source of water comes from food sources and broken down fats. In addition they have developed physiological methods to retain water, such as producing a concentrated urine. Another interesting phenomenon about these mammals is the behavior of eating stones before coming ashore. The true purpose of this behavior is not known. The stones are eliminated when they re-enter the water for migration, so it has been suggested that this phenomenon is in response to the long period of fasting. /=\
Northern Elephant Seal Migrations and Sea Movement
Breeding colony of northern elephant seals Foraging migrations by males and females are made separately, two times a year. Males travel as far north as the Aleutian Islands and the Gulf of Alaska. Females don't travel as far north, but instead migrate westward into the vast open ocean. The total distances covered by these animals each year during their migrations is as high as 21,000 kilometers. The males feed only in coastal waters while females feed in the open sea. Both sexes can be seen on shore most often from December through March, during the mating season and again beginning in April and continuing through August as they haul out for moulting.
Cheryl Lyn Dybas wrote in Natural History magazine: Elephant seals are drawn to a particular oceanographic feature — a boundary zone between two large rotating currents, or gyres. Along this boundary, the cold nutrient-rich waters of the subpolar gyre in the north mix with the warmer waters of the subtropical gyre to the south, driving the growth of phytoplankton and supporting a veritable feast of marine life. An oceanic surface feature linked with the boundary zone and caused by blooms of phytoplankton is visible on satellite images. It moves seasonally by as much as 600 miles, however. Some elephant seals don’t follow; they continue to target the deep boundary zone between the two gyres.[Source: Cheryl Lyn Dybas, Natural History magazine, September-October 2012]
Using data from nearly 300 tagged animals, marine biologist Daniel P. Costa showed that the elephant seals travel throughout the northeast Pacific Ocean on foraging trips in search of prey such as fish and squid. “For the first time, we can truly say that we know what elephant seals as a population are doing,” he says. The results were published in May 2012 in the journal PLoS ONE. A small number of elephant seals search for food in coastal regions, pursuing bottom-dwelling prey along the continental shelf. Among these is a female that feeds near Vancouver Island. She holds the record for deepest recorded dive by an elephant seal: 5,765 feet, more than a mile down.
Northern Elephant Seal Mating, Reproduction
Northern elephant seals are viviparous, meaning they give birth to live young that developed in the body of the mother, and engage in seasonal breeding. They also employ delayed implantation (a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months). They generally breed and give birth in California and Baja California, usually on offshore islands, from December to March, and fast during mating season, losing perhaps a third of their body weight. [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
Females may breed as often as once a year. The number of offspring is usually one but sometimes twins are born.The gestation period ranges from 10 to 12 months. Females reach sexual maturity at two to 10 years. On average females reach sexual maturity at age nine years. Males reach sexual maturity at two to 10 years. On average they do so around 9 years.
Female northern elephant seal with pup Northern elephant seals are are polygynous breeders with a social hierarchal mating system described as "female defence polygyny". . Males form harems usually when they are nine to 10 years of age, battling for status. Adult males use their large, inflatable noses during the winter breeding season to resonate sound when vocally threatening each other. [Source: NOAA]
Each dominant male controls access to mating opportunities with a group of females. Less dominant males are restricted to the outskirts of a colony and continually try to gain access to females, resulting in battles between males and aggressive charges by dominant males. Sub-dominant males usually run away but occasionally a male will challenge the dominant male in an attempt to take over the harem. According to Animal Diversity Web: Females release an audible "bawling" sound when a non-dominant male tries to mate with her. This results in a defense attempt by the dominant bull, who chases the less dominant male away. Occasionally the less dominant male becomes defiant and this can result in spectacular displays of threats and sometimes violent fighting. When a male wants to mate, he throws a flipper over the side of a female, grips her neck in his teeth and begins copulation. Resistance by a female only results in the male moving his large and heavy body on top of the female so she is unable to move. Aggressive interactions among males often result in elephant seal pups being killed by trampling. /=\
Northern elephant seals haul out of the sea and move to land birthing and breeding. Females come into heat only 19 days after giving birth. They remain receptive for about four days, during which mating occurs. Females become sexually mature at two years of age, but usually begin giving birth in the 4th year of life. Males are sexually mature at the age of six or 7, but only occasionally are allowed to mate before they reach the age of nine or 10 because of the hierarchy system of mating. Delayed implantation lasts for about three months, resulting in a total gestation time of nearly one year. This allows both birthing and mating to occur in the same time frame, during the short period of the year when the animals aggregate in terrestrial colonies. Interestingly, the embryo is never actually implanted, by definition of most mammals. Instead, it attaches only outwardly to the uterine wall throughout its development. /=\
Northern Elephant Seal Parenting and Offspring
Pups are born in early winter from December to January. Females come ashore and within a few days give birth to a pup conceived in the previous breeding season. The pups are weaned for about a month and just before her pup leaves she breeds again and then returns to sea. [Source: NOAA]
Young are relatively well-developed when born. Pre-fertilization protection is provided by females. During the pre-birth and pre-weaning stages provisioning and protecting is done by females. The weaning age ranges from 23 to 27 days.
Pups gain weight quickly during the period of lactation. Their mother’ milk is extremely high in fat. Newborns typically weigh about 47 kilograms (104 pounds) at birth. They weigh about 147 kilograms (324 pounds) and measure about 1.5 meters (5 feet) between 24 and 28 days old, when they are weaned. Northern elephant seal pups are black until they are weaned at about 6 weeks old and they molt and turn light silver. [Source: NOAA]
During weaning pups stay close to their mothers until the time that the mother leaves the pup behind to return to sea. Young pups left alone form groups or "pods", which remain on shore for up to 12 weeks without parental care. They learn to swim in the surf and eventually swim further out to sea for a short time to feed. Young male pups left to fend for themselves sometimes engage in an activity called "milk stealing". They attempt to nurse from lactating females still on the beach raising their young. It has been found that pups that successfully pull this off increasing their weight and overall health and have a significant advantage in survival and higher ranking later on in his life. ./=\
Young pups are quite vulnerable to death, particularly by predation by orcas, other toothed whales and sharks, and trampling. Trampling usually happens as a result of a large male defending its females, crushing the pup under his weight as he tries to quickly move toward an intruder. By some estimates as many as 10 percent of the young pups in a colony die this way each year.
Northern Elephant Seal, Humans and Threats
Elephant seal fishery in the 19th century Northern elephant seals are not endangered although they once were on the edge of extinction. They are designated as a species of least concern on the International Union for Conservation of Nature (IUCN) Red List and have no special status according to the Convention on International Trade in Endangered Species (CITES). Like all marine mammals, are protected by the Marine Mammal Protection Act (MMPA) throughout their range.
Northern elephant seals were once thought to be extinct due to commercial sealing in the 1800s. Populations of northern elephant seals in the U.S. and Mexico were all originally derived from a few hundred individuals surviving in Mexico. Its population began to steadily increase in the early 1900s. [Source: NOAA]
Northern elephant seals presume extinct in the 1880s, after being exploited by hunters, sealers and whalers mainly for the oil found in the animals' thick layer of blubber. A few animals were discovered in 1892 which were captured and killed for scientific study. Later, a population of about 20 to 100 individuals had survived on Guadalupe Island off Baja California. Studies have shown that all individuals of the current population are descendants of these few survivors. There are concerns that the lack of genetic variation could make the seals vulnerable to disease or reproductive failure. [Source: Karen Warburton, Animal Diversity Web (ADW) /=]
Humans utilize northern elephant seals them for tourism, research and education. They have been studied on research related to the effect of weightlessness on bone density because they spend 90 percent of their time in a neutrally buoyant environment. NASA has used this research in their efforts to counteract the effect of weightlessnes on bone density in astronauts. Because northern elephant seals can dive to extreme depths it has been suggested that they can greatly aid human efforts to explore and map the deep oceans once instruments that can withstand extreme pressures are developed. /=\
Northern elephant seals are a huge attraction for tourists to the Año Nuevo State Reserve in California. Elephant seals are the only known animals capable of filling collapsed lungs. Their lungs collapse during dives. The surfactant/lubricant responsible for this ability is being researched at the Scripps Institute in San Diego for the potential benefit to premature humans with immature lungs. /=\
Threats to northern elephant seals include entanglement in fishing gear, vessel strikes and marine debris. They can become entangled in fishing gear, either swimming off with the gear attached or becoming anchored. Once entangled, seals may drag and swim with attached gear for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury, which may lead to reduced reproductive success and death. Inadvertent vessel strikes can injure or kill seals. The projected increase in ship traffic arising from the opening of trans-polar shipping routes (as arctic sea ice continues to decline) will increase the risk of vessel strikes, and also increase ambient noise and pollution. [Source: NOAA]
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated June 2023