Northern elephant seals are important as predators on octopus, squid, small sharks, skates, and fish. In this way they impact the populations of these animals. They are also important as food for animals which prey on them, such as great white sharks and orcas.
Northern elephant seals try to feed by diving deep when in the water because the animals that view them as prey typically feed near the surface. Females migrate to the open ocean to feed in order to avoid predators as much as possible.
Known Predators:
Northern elephant seals are generally brown in color, however there are variations to this coloration. 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. Newborns have hair that is black in color until successfully weaned, when they shed their black coat and it is replaced by a lighter one. Countershading is a feature to all adults and newly weaned youngsters, displaying a darker color dorsally and a lighter color ventrally. They possess two, lobed hind flippers. Pinnae are absent, giving the ear the appearance of being flush with the skin. The most conspicuous feature to the male body is the inflated proboscis that adorns his face. This feature is absent in females and is larger than that of their slightly larger close relatives, southern elephant seals. Young males begin development of the proboscis at 2 years of age, but it is not fully developed until the animal reaches its 8th year of maturity. These mammals are among the largest of the group comprising aquatic carnivores in the Northern Hemisphere. Females typically weigh 600 to 900 kg and males, which outweigh females by 3 to 10 times, can top out at 2300 kg. Females reach a length of 3.1 m on average and males usually extend from 4.0 m to 5.0 m. Newborns typically weigh about 47 kg at birth. They weigh about 147 kg and measure about 1.5 m between 24 and 28 days old, when they are weaned. Teeth are dimorphic in the sexes with males having considerably enlarged canines that are used in fighting.
Range mass: 600 to 2300 kg.
Range length: 3.0 to 5.0 m.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes shaped differently; ornamentation
Because these animals spend such an extraordinary amount of time in the water, there are many gaps in how much we know about them. It is difficult to discern lifespans of these animals and what might be defined as a "natural" cause of death. Estimates of survival of reproductive females is 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%, at 2 years, 30%, and at 3 years, 20%. Adult males live an average of 11 to 13 years old. Young pups are quite vulnerable to death, particularly by predation 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% of the young pup population may perish this way annually.
Range lifespan
Status: wild: 18 (high) years.
Average lifespan
Status: wild: 9 years.
Typical lifespan
Status: wild: 13 (high) years.
Average lifespan
Status: wild: 6.5 years.
Average lifespan
Status: captivity: 15.0 years.
Northern elephant seals reside terrestrially on the sandy, rocky or muddy shores of the coastline, particularly on offshore islands. They typically aggregate in large groups while on land. These animals spend only 10% of their time on land, during reproduction and moulting. The other 90% is spent in the water, diving and foraging for food, and only 11% of this time in the water is spent at the surface. This means that an extraordinary 85-90% of their time is spent at sea and under water. These mammals can dive exceptionally deep, to 500 to 600 meters (almost 1 mile) on average and to record depths of over 1500 meters for extended periods of time (20 to 70 minutes).
Range depth: 1000 (high) m.
Average depth: 500-700 m.
Habitat Regions: temperate ; terrestrial ; saltwater or marine
Terrestrial Biomes: desert or dune
Aquatic Biomes: pelagic ; coastal
Other Habitat Features: intertidal or littoral
Northern elephant seals are found in the coastal waters of the Pacific Ocean from the Gulf of Alaska down to Baja California. Foraging migrations by males and females are made seperately, two times yearly. Males journey north to the Aleutian Islands and the Gulf of Alaska. Females don't travel as far north, but instead migrate further west to more open ocean. The total linear distances migrated by these animals each year has been recorded at 21,000 km. Seals 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.
Biogeographic Regions: nearctic (Native ); oceanic islands (Native ); pacific ocean (Native )
Northern elephant seals spend 90% 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. 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. Male foraging behavior is characterized by benthic dives to the sea floor. By contrast, females exhibit pelagic 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.
Foods eaten include: cephalopods, skates, small sharks, and fish.
Animal Foods: fish; mollusks
Primary Diet: carnivore (Piscivore , Molluscivore )
Northern elephant seals are a huge attraction for tourists to the Año Nuevo State Reserve in California. Here visitors can watch these magnificent animals from a safe distance, during breeding season. Northern elephant seals were once hunted for their blubber, which was refined to use as oil.
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.
Northern elephant seals have also been used in research related to the effect of weightlessness on bone density because they spend 90% 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.
Positive Impacts: ecotourism ; research and education
Northern elephant seals may consume some fish and other prey that are important to the fishing industry. However, their impact is probably exaggerated.
Northern elephant seals are not presently endangered. At one time, however, this species was thought to have been hunted to extinction. They were presume extinct by the 1880's, after being exploited by hunters and whalers seeking to use the animals' thick layer of blubber as an oil source. A few animals were then discovered in 1892 which were captured and killed for scientific study. Eventually, it was discovered that a population of about 20 to 100 individuals had survived. Studies have shown that all individuals of the current population, which has grown to over 175,000, are relatives of these few survivors. The population bottleneck that occurred during this time is of concern because genetic variation is reduced, creating the possibility for the population to be vulnerable to disease or reproductive failure.
US Migratory Bird Act: no special status
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
Perception Channels: tactile ; chemical
There is a definitive hierarchy structure to the mating system of these animals because they are polygynous and they aggregate in colonies on land during the breeding season. Each dominant male controls access to mating opportunities with a group of females. Bonner (1990) calls this mating system "female defence polygyny". Less dominant males are restricted to the fringes of a colony and continually try to gain access to females, resulting in battles between males and aggressive charges by the dominant male. Sub-dominant males usually run away but occasionally a male will challenge the dominant male in an attempt to take over the harem. 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. (Bonner 1990)
Mating System: polygynous
Northern elephant seals haul out for birthing and breeding from December to March. The 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 2 years of age, but usually begin giving birth in the 4th year of life. Males are sexually mature at the age of 6 or 7, but only occasionally are allowed to mate before they reach the age of 9 or 10 because of the hierarchy system of mating exhibited by these animals. (Reeves, et al. 1992; Bonner 1990) These animals display a phenomenon in their development cycle called delayed implantation. Delayed implantation lasts for about 3 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 these animals are aggregated 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. (Bonner 1990; Mathews 1952)
Breeding interval: Females may breed as often as once yearly.
Breeding season: Breeding and birthing occurs from December to March.
Range number of offspring: 1 to 2.
Average number of offspring: 1.
Range gestation period: 10 to 12 months.
Range weaning age: 23 to 27 days.
Range age at sexual or reproductive maturity (female): 2 to 10 years.
Average age at sexual or reproductive maturity (female): 9 years.
Range age at sexual or reproductive maturity (male): 2 to 10 years.
Average age at sexual or reproductive maturity (male): 9 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous ; delayed implantation
Average birth mass: 37500 g.
Average number of offspring: 1.
The pregnancy will ultimately last just under one year, as a result of delayed implantation. Parturition, which results in one offspring per year (although there have been occurrences of twins), will occur the following winter and lactation will follow for about 27 days before the pup is weaned. Pup weight gain during the period of lactation is phenomenal, the milk is extremely high in fat. During weaning the pup remains close to the mother until such a 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. An interesting phenomenon displayed by young male pups left to fend for themselves is that of "milk stealing". An attempt to nurse from lactating females still on the beach raising their young can give the successful pup a significant advantage in survival and higher ranking later on in his life by increasing his weight and overall health.
Parental Investment: no parental involvement; precocial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)
The northern elephant seal (Mirounga angustirostris) is one of two species of elephant seal (the other is the southern elephant seal). It is a member of the family Phocidae (true seals). Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. Sexual dimorphism in size is great. Correspondingly, the mating system is highly polygynous; a successful male is able to impregnate up to 50 females in one season.
The huge male northern elephant seal typically weighs 1,500–2,300 kg (3,300–5,100 lb) and measures 4–5 m (13–16 ft), although some males can weigh up to 3,700 kg (8,200 lb).[3] Females are much smaller and can range from 400 to 900 kg (880 to 1,980 lb) in weight, or roughly a third of the male's bulk, and measure from 2.5 to 3.6 m (8.2 to 11.8 ft).[4] The bull southern elephant seals are, on average, larger than those in the northern species, but the females in both are around the same size, indicating the even higher level of sexual dimorphism in the southern species.[5] Northern elephant seals typically live for around 9 years.[6] Both adult and juvenile elephant seals are bar-skinned and black before molting. After molting, they generally have a silver to dark gray coat that fades to brownish-yellow and tan. Adult males have hairless necks and chests speckled with pink, white, and light brown. Pups are mostly black at birth and molt to a silver gray after weaning.
The eyes are large, round, and black. The width of the eyes and a high concentration of low-light pigments suggest sight plays an important role in the capture of prey. Like all seals, elephant seals have atrophied hind limbs whose underdeveloped ends form the tail and tail fin. Each of the "feet" can deploy five long, webbed fingers. This agile, dual palm is used to propel water. The pectoral fins are used little while swimming. While their hind limbs are unfit for locomotion on land, elephant seals use their fins as support to propel their bodies. They are able to propel themselves quickly (as fast as 8 km/h) in this way for short-distance travel, to return to water, catch up with a female or chase an intruder.
Like other seals, elephant seals' bloodstreams are adapted to the cold in which a mixture of small veins surrounds arteries capturing heat from them. This structure is present in extremities such as the hindlimbs.
A unique characteristic of the northern elephant seal is that it has developed the ability to store oxygenated red blood cells within its spleen. In a 2004 study researchers used MRI to observe physiological changes of the spleens of 5 seal pups during simulated dives. By 3 minutes, the spleens on average contracted to a fifth of their original size, indicating a dive-related sympathetic contraction of the spleen. Also, a delay was observed between contraction of the spleen and increased hematocrit within the circulating blood, and attributed to the hepatic sinus. This fluid-filled structure is initially expanded due to the rush of RBC from the spleen and slowly releases the red blood cells into the circulatory system via a muscular vena caval sphincter found on the cranial aspect of the diaphragm. This ability to slowly introduce RBC into the blood stream is likely to prevent any harmful effects caused by a rapid increase in hematocrit.[7]
The northern elephant seal lives in the eastern Pacific Ocean. They spend most of their time at sea, and usually only come to land to give birth, breed, and molt. These activities occur at rookeries that are located on offshore islands or remote mainland beaches. The majority of these rookeries are in California and northern Baja California, ranging from Point Reyes National Seashore, California to Isla Natividad, Mexico.[8] Significant breeding colonies exist at Channel Islands, Año Nuevo State Reserve, Piedras Blancas Light, Morro Bay State Park and the Farallon Islands in the US,[9] and Isla Guadalupe, Isla Benito del Este and Isla Cedros in Mexico.[9] In recent decades the breeding range has extended northwards. In 1976 the first pup was found on Point Reyes and a breeding colony established there in 1981.[10] Since the mid-1990s some breeding has been observed at Castle Rock in Northern California and Shell Island off Oregon,[11] and in January 2009 the first elephant seal births were recorded in British Columbia at Race Rocks.[12] The California breeding population is now demographically isolated from the population in Baja California.[9]
Northern elephant seals exhibit extreme sexual dimorphism in their feeding behaviours. When the males leave their rookeries, they migrate northwards to their feeding grounds along the continental shelf from Washington to the western Aleutians in Alaska.[13][14] The males mostly feed on benthic organisms on the ocean floor.[13] When the females leave their rookeries, they head north or west into open ocean, and forage across a large area in the northeastern Pacific.[13] They have been recorded as far west as Hawaii.[13] Female elephant seals feed mainly on pelagic organisms in the water column.[13]
Vagrant elephant seals possibly appear on tropical regions such as at Mariana Islands.[15] Historical occurrences of elephant seal presence, residential or occasional, in western North Pacific are fairly unknown. There have been two records of vagrants visiting to Japanese coasts; a male on Niijima in 1989[16] and a young seal on beaches in Hasama, Tateyama in 2001.[17] A 2.5 meter female was found on Sanze beach, Tsuruoka, Yamagata in October 2017, making it the first record from Sea of Japan. This individual was severely weakened but showing signs of recovery after receiving medications at Kamo Aquarium, and the aquarium is discussing whether or not to release her.[18] Some individuals have been observed on the coast of northeast Asia. Certain individuals established haul-out sites at the Commander Islands in the early 2000s; however, due to aggressive interactions with local Steller sea lions, long-term colonization is not expected.[19][20]
Female elephant seals forage in the open ocean, while male elephant seals forage along the continental shelf.[13] Males usually dive straight down to the ocean floor and stay at the bottom foraging for benthic prey.[13] The females hunt for pelagic prey in the open ocean, and dive deeper (up to 1735 m, though on average about 500 m) and stay down longer than the males.[21][13] Female elephant seals have been tagged and found to dive almost continuously for 20 hours or more a day, mostly in 400 to 600 meter deep water, where small fish are abundant.[22]
Northern elephant seals eat a variety of prey, including mesopelagic fish such as myctophids, deep-water squid, Pacific hake, pelagic crustaceans, relatively small sharks, rays, and ratfish.[23][14][24] Octopoteuthis deletron squid are a common prey item, one study found this species in the stomachs of 58% of individuals sampled off the coast of California.[25] A female northern elephant seal was documented in 2013 by a deep sea camera at a depth of 894 m (2,933 ft), where it consumed a Pacific hagfish, slurping it up from the ocean floor. The event was reported by a Ukrainian boy named Kirill Dudko, who further reported the find to scientists in Canada.[26] Elephant seals do not need to drink, as they get their water from food and metabolism of fats.
While hunting in the dark depths, elephant seals seem to locate their prey at least partly by vision; the bioluminescence of some prey animals can facilitate their capture. Elephant seals do not have a developed a system of echolocation in the manner of cetaceans, but their vibrissae, which are sensitive to vibrations, are assumed to play a role in search of food. Males and females differ in diving behavior. Males tend to hug the continental shelf while making deep dives and forage along the bottom,[13] while females have more jagged routes and forage in the open ocean.[13] Elephant seals are prey for orcas and great white sharks. Both are most likely to hunt pups, and seldom hunt large bull elephant seals, but have taken seals of all ages. The shark, when hunting adults, is most likely to ambush a seal with a damaging bite and wait until it is weakened by blood loss to finish the kill.[27]
Northern elephant seals return to their terrestrial breeding ground in December and January, with the bulls arriving first. The bulls haul out on isolated or otherwise protected beaches, typically on islands or very remote mainland locations. It is important that these beach areas offer protection from the winter storms and high surf wave action.[28] The bulls engage in fights of supremacy to determine which few bulls will achieve a harem.[29][30]
After the males have arrived to the beach, the females arrive to give birth. Females fast for five weeks and nurse their single pup for four weeks; in the last few days of lactation, females come into estrus and mate.[31] Mating behavior relates to a social hierarchy, and stronger males are considered 'higher rank' than those smaller and weaker.[32] In this polygynous society, a high-ranking bull can have a harem of 30–100 cows, depending on his size and strength. Males unable to establish harems will wait on the periphery, and will try to mount nearby females. Dominant bulls will disrupt copulations of lower-ranking bulls. They can mount females without interference, but commonly break off to chase off rivals.[29] While fights are not usually to the death, they are brutal and often with significant bloodshed and injury; however, in many cases of mismatched opponents, the younger, less capable males are simply chased away, often to upland dunes. In a lifetime, a successful bull could easily sire over 500 pups. Most copulations in a breeding colony are done by only a small number of males and the rest may never be able to mate with a female.[30] Copulation is most often on land, and takes roughly five minutes.[33] Pups are sometimes crushed during battles between bulls.[28][30]
After arrival on shore, males fast for three months, and females fast for five weeks during mating and when nursing their pups. The gestation period is about 11 months. One study observed the vast majority of births to take place at night, and in the aforementioned harems. Immediately after birth, a female will turn to her pup and emit a warbling vocalization to attract them, and will continue to throughout the nursing period.[34] Sometimes, a female can become very aggressive after giving birth and will defend her pup from other females. Such aggression is more common in crowded beaches.[35] While most females nurse their own pups and reject nursings from alien pups, some do accept alien pups with their own. An orphaned pup may try to find another female to suckle and some are adopted, at least on Año Nuevo Island.[28][31] Some pups, known as super weaners, may grow to exceptionally large sizes by nursing from other females in addition to their mothers.[36][37] Pups nurse about four weeks and are weaned abruptly before being abandoned by their mother, who heads out to sea within a few days. Pups gain weight rapidly during the nursing period, and weigh 300-400 pounds on average upon being weaned.[34] Left alone, weaned pups will gather into groups and stay on shore for 12 more weeks. The pups learn how to swim in the surf and eventually swim farther to forage. Thus, their first long journey at sea begins.
Elephant seals communicate though various means. Males will threaten each other with the snort, a sound caused by expelling air though their probosces, and the clap-trap, a loud, clapping sound comparable to the sound of a diesel engine. Pups will vocalize when stressed or when prodding their mothers to allow them to suckle. Females make an unpulsed attraction call when responding to their young, and a harsh, pulsed call when threatened by other females, males or alien pups. Elephant seals produce low-frequency sounds, both substrate-borne and air-borne. These sounds help maintain social hierarchy in crowded or noisy environments and reduce energy consumption when fasting.[38]
Beginning in the 18th century, northern elephant seals were hunted extensively, almost to extinction by the end of the 19th century, being prized for oil made from their blubber, and the population may have fallen as low as only 20-40 individuals.[1] In 1874, Charles Melville Scammon recorded in Marine Mammals of the Northwestern Coast of America, that an 18-ft-long bull caught on Santa Barbara Island yielded 210 gallons of oil.[39] They were thought to be extinct in 1884 until a remnant population of eight individuals was discovered on Guadalupe Island in 1892 by a Smithsonian expedition, who promptly killed several for their collections.[40] The elephant seals managed to survive, and were finally protected by the Mexican government in 1922. Since the early 20th century, they have been protected by law in both Mexico and in the United States. Subsequently, the U.S. protection was strengthened after passage of the Marine Mammal Protection Act of 1972, and numbers have now recovered to over 100,000.
Nevertheless, a genetic bottleneck experienced by Northern elephant seals during the nineteenth century made them more susceptible to disease, environmental changes and pollution.[41][42] This bottleneck caused a sharp loss of genetic diversity and increased homozygosity in the surviving population, and also a decreased number of haplogroups.[43]
In California, the population is continuing to grow at around 6% per year, and new colonies are being established; they are now probably limited mostly by the availability of haul-out space. Their breeding was probably restricted to islands, before large carnivores were exterminated or prevented from reaching the side of the ocean.[44] Numbers can be adversely affected by El Niño events and the resultant weather conditions, and the 1997–98 El Niño may have caused the loss of about 80% of that year's pups. Presently, the northern elephant seal is protected under the federal Marine Mammal Protection Act and has a fully protected status under California law (California Fish and Game Code [FGC] § 4700).
While the population is rising in the state of California, some colonies farther south are experiencing declining populations, likely due to rising sea and air temperatures. In Baja California, the two largest colonies, in Guadalupe and San Benito, have seen consistently declining numbers for the past two decades. Seeing as populations farther north are consistently increasing, it has been hypothesized that this discrepancy is due to a change in migration patterns.[45] As sea and air temperatures rise, Northern elephant seals may not be migrating as far south as they have previously. The climate is expected to continue warming, and southern populations are expected to continue falling.[45]
Populations of rookery sites in California have increased during the past century.[1] At Año Nuevo State Park, for example, no individuals were observed whatsoever until 1955; the first pup born there was observed in the early 1960s. Currently, thousands of pups are born every year at Año Nuevo, on both the island and mainland. The growth of the site near San Simeon has proved even more spectacular; no animals were there prior to 1990. Currently, the San Simeon site hosts more breeding animals than Año Nuevo State Park during winter season.
{{cite journal}}: CS1 maint: unfit URL (link) The northern elephant seal (Mirounga angustirostris) is one of two species of elephant seal (the other is the southern elephant seal). It is a member of the family Phocidae (true seals). Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. Sexual dimorphism in size is great. Correspondingly, the mating system is highly polygynous; a successful male is able to impregnate up to 50 females in one season.
