Elephant Seal

Common Name: Northern Elephant Seal

Class: Mammalia

Order: Pinnipedia

Family: Phocidae

Genus: Mirounga

Species: Mirounga augustirostis

 

Taxonomy/Description

Northern Elephants Seals belong to the Mammalian Order Pinnipedia, in the family Phocidae.  Other members of Phocidae include harbor seals, gray seals, and monk seals.  Phocids are referred to as true seals.  They are distinguished from other pinnipeds by their inability to support their body using their hind limbs.  The Northern Elephant Seal's genus name, Mirounga, is derived from the Australian Aboriginal word for seal, miouroung.  Its specific name, augustirostis,  means "narrow rostrum".  This is referring to the Northern Elephant Seal's long snout, which is narrower than the Southern Elephant Seal's snout.

Elephant Seals are known for their sexual dimorphism, males can be almost five times larger than females in this species.  Northern Elephant Seal males can weigh over 5,000lbs.  However, females of this species only grow as large as 1,400lbs. Another feature of these seals that relates to male-female differences also explains how this species got its name.  The male seal's proboscis is an enlarged trunk-like structure. 

Habitat/Diet

The Northern Elephant Seal can be found along the Pacific coast of North America from Baja California up to the Aleutian Islands of Alaska.  Squid, rays, skates, small sharks, and Pacific hake compose the elephant seal's diet.  Elephant seals can hold their breath for up to 80 minutes and dive to depths of 5,000ft to search for prey.  The average length of time an elephant seal will hold its breath for is 20 minutes.

Behavior Reproduction

These seals were named "elephant" because their "noses" resemble the trunks of elephants.  Despite this superficial similarity, the seals' proboscis has a different purpose entirely.  The male elephant seal uses his " trunk" as a resonance chamber to help make its roars sound as loud as possible.  This is particularly important during the breeding season when elephant seals haul out on beaches to mate.  

 

The Northern Elephant Seal's breeding season begins in early December.  This is when the males begin to establish their territories while waiting for females to arrive.  By the middle of December pregnant females start to arrive on shore to find a spot on the same beaches to give birth.  They give birth around the third week in December and immediately start to nurse their young.  This time period known as the pupping season continues until the first week in February.  It is only after the females have given birth, that they begin to mate with the males on the beach. 

The breeding male and female elephant seals remain on the rookery and do not feed during this whole time period.  They therefore must spend these 3-4 months subsisting on the fat stores on their body.  One can thus easily understand why it is advantageous for both male and female elephant seals to go into their breeding season with ample stores of fat.  Large size gives males a greater advantage while establishing dominance on a beach, and it allows them to hold onto their territories 24hrs per day while living off their fat reserves.  

Fat also provides an advantage to females by giving them the nutritive energy to invest into their pups.  Elephant seal milk is very oily and high in fat content.  A well nursed pup grows from 20 pounds at birth to 150 pounds in only three weeks!  In the elephant seal world, a fat baby is a healthy baby, and that depends entirely on its mother's ability to tap her own fat reserves in producing milk.  

An elephant seal's size is so important that some elephant seal pups will nurse not only from their own mother but will steal milk from other females as well.   This will not only help them survive immediately when they return to sea, but it will also make them grow to a larger size which will aid them in the future when they return to the rookery to mate.  

Another very important time period in an elephant seal's life is its molting period, which takes place once a year.  This is the time where elephant seals shed their old coat of fur and grow in a new one.  Elephant Seals must come to land while molting.  This is for three reasons.  First is because they are very susceptible to the cold while losing their old fur.  Secondly, their old coat needs to be warm and dry in order to flake off.  Third, they use the sand and the rocks on the beach to rub up against to help get their old coat off.  

Conservation

Elephant Seals were easily hunted for their meat because of the return to their customary beaches each year for breeding and molting.  They are slow moving on land.  This led to massive slaughtering of elephant seals species in both the Northern and Southern Hemispheres.  Due to the careful protection of their rookeries, the elephant seal population on the west coast of North America is starting to make a comeback.  But we must remain vigilant and extend this same level of protection to other areas throughout the Pacific Ocean so that this species will once again thrive.  

 

 

Content provided by Canisius College students under the direction of Michael Noonan, PhD.