Northern Elephant Seal
(Mirounga angustirostris)

IUCN STATUS (2010) - LEAST CONCERN

Distribution and Numbers
Renowned for their long migration distances and their incredible diving abilities, Northern elephant seals, so named because of their long elephant-like noses, breed, give birth and moult in California and Baja California, mostly on offshore islands. Outside the breeding and moulting seasons they feed as far north as the Gulf of Alaska.

There are an estimated 84,000 Northern elephant seals in California, while in 1991 the Mexican population was estimated to be about 32,000.

Mirounga angustirostris - Image 1

Photo: Phillip Colla,
Phillip Colla Wildlife Photography
Status
Northern elephant seals were almost hunted to extinction for their blubber oil in the 19th century, only an estimated 100-1,000 individuals on the Mexican Isla de Guadalupe managing to escape the hunt. The species was protected under Mexican and U.S. law in the early 20th century and since then has made a remarkable comeback. In California the population is continuing to grow at an average annual rate of 20-30% and new rookeries are being established, some of which were not historical colony locations. The population is likely larger than prehistorical times because elephant seals probably bred only on islands due to avoidance of predators such as grizzly bears. Numbers may now be approaching peak levels and certainly at some colonies, such as the Farallon Islands, terrestrial haulout space is limited. In Mexico the population is currently stable or slowly decreasing, although increasing numbers of individuals are being observed in the Gulf of California.
Mirounga angustirostris - Image 2

Photo: Phillip Colla,
Phillip Colla Wildlife Photography
All individuals alive today are descended from a small number of seals and the genetic population bottleneck caused by this near-extermination may have repercussions in terms of the limited genetic diversity of the species. Northern elephant seals can be badly affected by El Nino events and the resultant weather conditions. It was reported, for example, that during the 1997-98 El Nino the mortality of Northern elephant seal pups at sites in California, such as Point Reyes, was around 80%. Severe winter storms, elevated sea levels, heavy rains and very high tides combined to submerge colonies and wash away pups. Similar mortality was observed during the 1982-83 El Nino event. The overall effects of the 1997-98 El Nino have still to be evaluated, but it is known that the Farallon Islands colony decreased by nearly half due to habitat changes caused by winter storms during the event. There is some mortality, estimated to be less than 100 individuals per year, due to entanglement in the nets of Californian fisheries, particularly gillnet fisheries. The swordfish and shark drift gillnet fisheries in Mexico also result in bycatch of the species.
A very small number of elephant seals are killed in the United States by deliberate shooting, collisions with boats and collisions with cars on land. The Northern elephant seal was previously listed as an Appendix II species under CITES but was deleted from the list in 1992. The species is protected in the U.S. under the Marine Mammal Protection Act of 1972 and in Mexico under the Ley General de Vida Silvestre NOM-059-ECOL-1994.

Lifestyle
Northern elephant seals migrate twice a year between the Californian and Mexican beaches and their feeding areas in the north Pacific Ocean. The adult males feed in the Gulf of Alaska and near the eastern Aleutian Islands, while the adult females feed further south between 40-45°N. No other mammal shows this biannual migration pattern nor migrates over such a long distance. The first migration takes place when the winter breeding season is over, the second after the summer moult. Overall the bulls spend about 250 days at sea each year and travel at least 21,000km, the females spending about 300 days at sea and travelling at least 18,000km.

Seals congregate onshore three times a year: during the breeding season, the moulting season, and the juvenile period in the autumn. The breeding season takes place from December until March. The large adult males arrive at the start of the season and compete, usually by fighting, for a prominent position in a hierarchy that allows the most dominant males to have greater access to females. Most births take place in January, pups being born 2-7 days after the mother has arrived at the beach. The pups are born with black hair which is relaced by a silvery coat after they are weaned, about 3-4 weeks later.

The mother mates with a male usually about 3-5 days before her pup is weaned and then, after her pup is weaned, she leaves. The pup then lives off its blubber reserves for 1-2 months before going to sea to hunt for its own food. Both adult males and females do not feed for the entire time that they are ashore, some males for up to 3 months, and they lose approximately 36% of their weight during this period.

Northern elephant seals undergo an annual moult, called a "radical moult" because the fur comes off in sheets. The seals congregate onshore to moult during the summer months between March and July. This moulting period is protracted because each sex and age class moults at a different time, beginning with immature seals early in the season and ending with the bulls which moult in July. Individual seals remain mostly onshore during the moult, for around 2-3 weeks. The Northern elephant seal coat is dark grey to brown.

In the autumn, prior to the breeding season, juvenile seals congregate at the colony sites for around 2 months, beginning in late September and extending through to November.

Mirounga angustirostris - Image 3

Photo: Phillip Colla,
Phillip Colla Wildlife Photography
Northern elephant seals, like their relations the Southern elephant seals, are renowned for their ability to remain submerged for very long periods of time and to dive to great depths while feeding, males to 350-800m on average and females to 300-600m. Their dives of long duration, averaging 21 minutes for males and 17 minutes for females, are interrupted by only brief intervals, mostly less than 3 minutes, at the surface. The deepest dives are beyond 1,500m deep and last for 1.5-2 hours. The seals repeat these dives almost continuously for 2-8 months and spend 80-95% of their time at sea submerged. Researchers have identified five different dive patterns, these patterns associated with travel, sleep and foraging. Northern elephant seals are also in the habit of holding their breaths for as long as 25 minutes while hauled out.
Cephalopods are an important component of the Northern elephant seal diet. Other prey includes Pacific whiting, skates, rays, sharks and pelagic red crabs. Northern elephant seals are preyed on by great white sharks, a significant cause of mortality in juvenile seals, and sometimes also by killer whales.

Statistics
There is a great difference in size between the sexes with adult males weighing two to seven times heavier than adult females, adult males measuring up to 4.5m long and weighing up to 2,300kg, adult females measuring up to 3.6m long and weighing up to 750kg. Pups are born about 1.5m in length and weighing about 30kg. Females reach sexual maturity at 3-5 years of age, males at 4-6 years although prime breeding condition for males is not reached until 9-12 years. Males can live up to 17 years, females up to 22 years.