Northern Elephant Seals 

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Scientific Classification

Order: Carnivora

Sub-order: Pinnipedia

  • Means “feather” or “fin footed.” (in reference to the shape of their flippers)

  • Pinnipeds are characterized by large body size; presence of fur, blubber or both; fusiform bodies; ability to move around on land or ice; delayed implantation and superior diving abilities (Reynolds et al., 1999).

 Family: Phocidae

  • Includes all true, earless seals.

  • Characterized by the following traits: Inability to rotate pelvic girdle (hind flippers) for locomotion on land. Therefore must crawl/undulate on bellies rather than walk on land as with otariids. Back flippers provide propulsion during swimming.

Sub Family: Monachinae

  • Characterized by annual ‘catastrophic molts’. Epidermal layer of skin molted along with fur. All other phocids molt only fur annually.

Genus: Mirounga

  • Northern & Southern elephant seal

  • Characterized by extreme sexual dimorphism: males weigh 8-10 more than females.

  • Males have an enlarged proboscis or ‘trunk’, hence the name elephant seal.

Species: angustirostris largest pinniped outside Southern elephant seal (Ling & Bryden, 1981). Largest seal in the northern hemisphere.

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General Information

Fossil Record

All pinnipeds evolved from a common carnivore ancestor approximately 25 million years ago and diverged into the current families 15 million years ago (10 million years later). Their carnivore ancestor has not been identified yet, but may have been bear- or otter-like (Boness and Bowen, 1996). Three extant lineages of pinniped include: Otariidae (sea lions & fur seals), Phocidae (true/earless seals) and Odobenidae (walrus). Northern and Southern elephant seals diverged about 4 million years ago (Arnasson et. al, 2006).

Distribution

  • The northern species has a more limited distribution. There are 15 breeding colonies between Pt. Raines in northern California to the Baja Peninsula in Mexico (Farallon Island to Guadalupe Island). Most colonies are found on offshore islands but a small number do appear on the mainland.

  •  The southern species is more widely dispersed and are sub-Antarctic, although a few can be found on the Antarctic mainland.

Habitat

80% of their year spent at sea where they build up massive blubber stores by foraging in order to survive fasting periods during molting and breeding haul outs on sandy shores.

Population

Northern species is undergoing a population increase and range extension. They are expanding at a 6% rate per year; southern species declining in places up to 66% (unclear why)

 Diet

  • Prey on deep water squid and fish. Little scientific information published on diet of either species.

  •  Northern species differ sexually in feeding areas—males more northerly off continental shelf and females more northwesterly—deep ocean

Anatomy and Physiology

Appearance

Second largest pinniped in the world to the southern species; Pups are black until they are weaned at about 4 weeks old, they molt and turn light silver; adults are dark brown or gray

Head

Northern males have larger proboscis and more developed chest shield (neck chest and shoulders- thickened skin-scarring from fights) than southern species. Proboscis is inflatable for dominance displays. Northern’s chest shield has reddish hue. Females have no proboscis or chest shield.

Northern females have a narrower/flatter nose than southern species.

 Size Difference

Extreme sexual dimorphism with males being much larger than females.

Maximum Adult Male Weight/Length in the Wild

2300 kg (5070 lbs.) (southern species up to 3700kg or 8157 lbs.)/ 4 m (13 feet) 

Maximum Adult Female Weight/Length in the Wild

800kg (1763 lbs.) / 3 m (10 feet)

Swimming, Diving and Thermoregulation

Dive Depth/Duration

  • Adult females: 400-800 m (1312ft-3624 ft.) in deep open ocean/ 20 minutes

  •  Adult males: Shallower dives to feed over continental shelves/ 30 minutes

Maximum Dive Depth/Duration

Dive to depths over 1500 m (4921ft.) up to 2 hours

Behavior

Spend 90% of their time submerged when at sea. Most of that time is foraging but traveling and resting take place at depths of 200+m ( 656+ ft.) (Hindell, et al 2000; Lester and Costa 2006; Davis et al 2007)

Experience a ‘catastrophic molt’: shed layer of skin as well as all fur. Need to haul out to conserve body heat in order to send supplies of blood to body surface for new skin and hair. Entire molt lasts 3-5 weeks. They fast the entire time relying on blubber (Champagne et al 2006). Timing of molting varies with age/sex class and with females’ fertile state. (Kirkman et al 2003)

Social Behavior

Typically antisocial outside of breeding and pupping season.

Vocalizations

Vocalizations convey info on age, size and resource holding potential (Sanvito et al 2007)

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Reproduction and Maternal Care

Males sexually mature around 7 years. Age at first breeding for females is between 3 to 8 years – average varies with species, population status and environment (Sydeman and Nur 1994).

 Mating Season

Males haul out on beaches in December; pregnant females haul out in large numbers in December to January. Females give birth 2-5 days after arriving. Breeding occurs from December to March.

Weight at Birth

Pups weigh 30-40 kg (approx. 75 lbs.) at birth. At weaning pups are: 140-150kg (308 lbs.-330 lbs.).

Nursing

Northern species nurse a few days longer than southern. 26-28 days.

Mating

Polygynous mating strategy. Females come into estrus several days before weaning pups and are mated by dominant males.

Male Territorial Behavior

Large proboscis of males plays key part in dominance displays with other males (Sanvito, et al 2007) Alpha males preside over ‘harems’ of females. Males fight to acquire alpha position. Successful males have almost exclusive access to harems up to 100 females—reproductive benefits of success high 

Migration after Breeding

Disperse widely during non-breeding cycle – many take a round

trip of 10,000 km (6,213 miles) —many make it twice due to breeding and molting separate events—return to same breeding grounds for breeding and molt

Gestation

Delayed implantation as with all pinnipeds. Egg is fertilized after mating but remains dormant for 2-3 months. Gestation lasts about 11 months.

Maternal Care

Females stay with pup throughout lactation period, fasting entire time.

Pup Behavior

After weaning, pups spend 4-6 weeks teaching themselves to swim, and hunt. Rely heavily on blubber from mom until able to hunt efficiently. Pups spend 6 months at sea after leaving beach: 30% die during this time.

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Other Information

Maximum Lifespan

13-19 years, with females living longer than males

Predators and Natural Threats

Starvation and infection. Predation risk by sharks and killer whales unknown.

Population

U.S. population estimate in 2010 is between 81,370 - 179,000, based on extrapolation from pup births. Estimation is difficult due to the species spending so much time dispersed at sea.

Conservation

  • Northern species hunted almost to extinction in the 19th century to less than 100 animals on a single island by 1890. This created an intense genetic bottleneck. All genetic diversity is gone from population. Southern population not hunted as extensively due to wider dispersal.

  • Biggest conservation concern is competition from fisheries, entanglement in marine debris, climate change and boat collisions.


References

Berta, 2009. Pinniped Evolution in: Encyclopedia of Marine Mammals, second edition.

Bowen, Beck and Austin, 2009. Pinniped Ecology in: Encyclopedia of Marine Mammals, second edition.

Boyd, 2009. Pinniped Life History in: Encyclopedia of Marine Mammals, second edition.

Hendell & Perrin, 2009. Elephant Seals Mirounga angustirostris and M. leonine. In: Encyclopedia of Marine Mammals, 2nd edition.

National Marine Fisheries Northern Elephant Seal Species Page: http://www.fisheries.noaa.gov/pr/species/mammals/seals/northern-elephant-seal.html

Pabst, et. al. 1999. The Functional Morphology of Marine Mammals. In: The Biology of Marine Mammals. Eds. Reynolds and Rommel.