Elephants of the Deep
What are Elephant Seals?
Elephant Seals are divided into two species, the Northern elephant seal (Mirounga angustirostris) and the Southern elephant seal (Mirounga leonine). The Northern Elephant Seal inhabits offshore islands along North America’s Pacific coast, whilst the Southern Elephant Seal is found in Antarctic and sub-Antarctic waters. Northern Elephant Seals can reach sizes of up to 16 feet long, making them one of the largest seal species in the world, second only to the Southern Elephant Seal that can be over 20 feet long. Elephant Seals do not get their name from their size, but rather their trunk-like snouts.
Mating and Reproduction
During the breeding season, male Elephant Seals will designate and protect territories. Within this territory males will collect a harem. These harems usually consist of 40-50 females, which are much smaller than the males. Males will fight for mating dominance whilst on land, these fights will begin with roaring and aggressive posturing and will often end with bloody fights. The roars
used to ward off other males are generated by the proboscis (nose) of the seal, which can be expanded to amplify sounds that can be heard several miles away. Males may be forced to defend their territory for several months and are unable to hunt. Females will give birth in late winter to a single pup after an 11-month pregnancy and nurse for a month, they do not feed for this month and both female and pup survive on reserve energy stored within blubber.
When not on land, Elephant Seals will migrate great distances at sea in search of food and will spend months at sea during migrations, continuously diving to great depths in search of food. The Northern Elephant Seal will migrate twice a year and is the only mammal to do so, covering a distance of around 34,000km per year. This is the longest distance traveled during a migration by any known mammal. Despite inhabiting large colonies whilst on land, whilst at sea Elephant Seals travel alone, only returning to colonies during winter months to breed, give birth and molt. Elephant Seals will molt from April through to May, after breeding through the winter months. Both male and female Elephant seals spend large periods of time at sea, however their migration routes differ. Males will follow a much more consistent route whilst females will vary migration patterns based on the abundance of food.
Each year, beginning around March, elephant seals undergo a “catastrophic molt”, Returning to the shores on which mating took place a few weeks prior. During the catastrophic molt seals will remain ashore for about a month in order to shed all of their fur. The fur sheds in patches, revealing a new dark grey layer of fur beneath. This grey fur will gradually change colour and become brown. Elephant Seals will not hunt during the molt, remaining on the beach until the fur has been replaced.
Both species of Elephant Seal will dive to great depths to locate food. Northern Elephant Seals will hunt at night, diving to depths of 300-800 metres. Southern Elephant seals dive to depths of up to 1,550 metres, however the largest recorded dive for a Southern Elephant seal is 2,388 metres. Elephant Seals have large eyes and rely on sight and vibrissae (whiskers) to hunt, detecting bioluminescence and nearby movement. Thick blubber protects them from the cold at such depths and they can remain submerged for up to two hours. To remain beneath the surface for so long, elephant seals possess a large volume of blood to maximise haemoglobin content and store more oxygen, more oxygen is stored within their muscles. As well as this, Elephant Seals slow their heart rate and divert blood away from extremities to focus on vital organs such as the heart, brain and muscles. As many marine organisms will migrate to greater depths during the day via a process known as diel-vertical migration, being able to reach these greater depths provides many advantages. One such advantage is the reduction in competition as few other marine mammals can reach these depths to forage for food. Another important advantage is avoiding potential
predators whilst at these depths. Killer Whales are predators of Elephant Seals and lurk in shallower waters. However, whilst Elephant Seals have a greater chance of avoiding these predators, mortality rates are still high. Feeding habits between males and females also differ, with males diving to greater depths and foraging along the ocean floor whilst females hunt in the open ocean at shallower depths further above the ocean floor. However, it is at these depths that Killer whales are more prevalent, increasing the risk of predation.
Hunted to the Brink
Both Elephant Seal species are at little risk of extinction, with both having an IUCN status of least concern. However, this was not always the case. In the 19th century blubber oil from northern Elephant Seals was a valuable commodity. This demand led to the Northern Elephant seal very nearly being hunted to extinction with only 100-1,000 surviving on the Mexican Isla de Guadalupe. They became a protected species under US and Mexican law in the early 20th century and have made an impressive resurgence, with 84,000 seals in California and 32,000 in Mexico as of 1991.