Thursday, July 22, 2010

Elephant Seal

The genus Mirounga holds two extant species, the Northern Elephant Seal (Mirounga angustirostris) and the Southern Elephant Seal (Mirounga leonina). The two species, predictably enough, reside in their respectively named hemispheres. The Northern Elephant Seals are often found on offshore islands and along the California coast. Southern Seals live in Antarctica, splitting time (depending on the season) between the mainland and the offshore pack ice.

Arguing Males from Friends of the Elephant Seals
Southern Elephant Seals are the largest of all the seals. The heaviest males recorded were over 8,000lbs. Both the Southern and Northern seals demonstrate extreme sexual dimorphism. Females rarely weigh much over 1,000lbs, and only grow to be about half as long as the males. They also do not sport the species' naming feature: the elephant trunk-like nose that is exclusive to the males. These noses assist the males in making loud, resonating sounds during the breeding season. Both the males and females lose a large amount of their body weight during that season, as they do not feed until the pups are weaned. Females can lose 35% of their overall mass.

The breeding season is interesting for the Elephant Seal. Males come ashore and fight each other, often brutally, for mates. Elephant Seals are polygynous, with one male breeding with a large number of females. After the dominant males have established themselves, the female arrive and give birth to the pups that they have been pregnant with for the past year. While they are nursing their pups, they will mate again with one of the males. Once their pups are weaned and mating is complete, the seals return to the sea. It is possible for females to give birth to ten pups over their lifetimes, and their overall life expectancy is a few years longer than the males.

Image from ItsNature
As previously mentioned, the Northern Elephant Seals can be found along the California coast. One site in particular houses a large colony that comes in year round to perform various functions. Año Nuevo state park sees thousands of Elephant Seals each year, either breeding, birthing, or molting. I was lucky enough to visit this place a few years back during the adult male molting season, and even from a pretty far distance back you can appreciate just how massive these pinnipeds are!

Both Northern and Southern Elephant Seals were hunted to near extinction for their oil during the 19th and early 20th century. Populations are now protected, and the Northern species has been steadily growing. The Southern Elephant Seals, however, have been experiencing a population decline in recent years. The exact reason for this is unknown, but it may just be that without hunting, the population has grown faster than the prey can sustain.

Thanks to John for the suggestion!


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