The Northern Elephant Seal (Mirounga angustirostris) gets its common name from the elephant-like snout on the faces of the males. The latin name means to have a narrow beak, which comes from a historical comparison with its larger relative, the Southern Elephant Seal (Mirounga leonina). The species ranges throughout the eastern side of the North Pacific Ocean from the Aleutian Islands of Alaska down as far as Baja California, Mexico. Despite heavy exploitation in the past which lead to near extinction, M. angustirostris has managed to recover sufficiently to currently be classed as Least Concern. Estimated population size = 239,000.
M. angustirostris are extremely large true seals, second in size only to their southern hemisphererelatives (males ♂ up to 5 m long/ 2,200 kg, females ♀ up to 3 m/ 800 kg). Fore flippers are small relative to the body, but also long and slender with thick, tough claws, while hind flippers are slender too. Their lengthy bodies are heavy and robust, with very thick necks, particularly the fully grown males. There is a huge degree of sexual dimorphism in elephant seals, meaning that the males and females differ in appearance. Male heads are large and bulbous, and nearly square shaped, with an elongated proboscis (or nose), which generally hangs down in front of their face, and females by comparison have rounder heads with broad, blunt muzzles and no proboscis. M. angustirostris are usually dark brown in males, to dusky brown or sandy in females, and another obvious feature of mature males is a hairless and pink-tinged neck with scarring and sometimes bleeding from intraspecific altercations.
Feeding behaviour:
M. angustirostris are known to be excellent divers who regularly swim at depths of 500-1000 m, and sometimes deeper. Therefore it is not surprising that a large proportion of their diet is made up of deep-sea and twilight zone fish, and squid. They have also been known to take crustaceans, cephalopods, sharks and chimaeras. It is noted that males and females vary here too, with males foraging along the benthos and females hunting for pelagic prey in the open ocean.
Breeding behaviour:
Sexual maturity – males ♂ 4-6 years old/ females ♀ 3-4 years old.
With a strongly polygynous mating system, M. angustirostris arrive at the beaches first during breeding season and engage in highly aggressive combat with other males in order to establish a hierarchy and gain access to a harem of females. During a season, the most successful males can mate with upwards of 50 females. Mating takes place on land and gestation lasts 11 months, with a period of delayed implantation. Pups are then born in the winter, from December through to March, with a warm, black lanugo which only starts to moult into a dark grey/ silver juvenile coat after about 3-5 weeks. Females will fast for the full ~ 4 weeks of nursing, after which the pups are weaned and left to complete their moult and fully develop physiologically for a further 4-6 weeks. They will then travel in groups for a while, learning to forage before heading deeper out to sea. Both adult sexes return again to land to undergo a catastrophic moult (fur and epidermis) between April and July, females first followed by males. Maximum life expectancy for M. angustirostris is around 25 years, but usually considerably less in males.
