The Amazing Adaptations of Northern Elephant Seals

By Susan Rothrock Deo

Featured image by Karen Schuenemann. More photos by her and Charles Conklyn, Paul Blieden, Susan Deo, Ariel Swartley and Ming H2 Wu in the slideshow

Have you seen them hauled out on a beach, lazing in the sun, or scooting their tremendous bodies across the sand at surprising speed? Have you heard them snort, whimper, belch, scream, squeak, roar or hiss? One doesn’t soon forget an encounter with the amazing northern elephant seal, Mirounga angustirostris, the second largest seal in the world, the loudest animal on land, and the deepest diver of all air-breathing vertebrates. 

The elephant seal is in the order Pinniped, which means fin or feather foot and includes seals, sea lions and walruses. Pinnipeds are marine mammals because they spend most of their time at sea. Unlike whales and dolphins, though, they come to land to mate, give birth and molt (shed their fur and some skin). 

It’s amazing how well adapted northern elephant seals are to this amphibious life. Because pinnipeds spend some time on land, we are a bit more familiar with them than we are with other marine creatures. For a long time we had no idea how elephant seals spent the majority of their lives because they were seldom seen at sea, where they spend eighty percent of their time. We knew they dove deep because deep-sea squid and fishes were found in the stomachs of dead seals.

In the early 1980’s scientists attached small recording devices to the foreheads of a few male and female northern elephant seals. Their first attempts to record dives failed because the devices didn’t survive the pressure and depth. With stronger recording devices, scientists discovered northern elephant seals spend up to 86% of their time at sea submerged, taking dives of 20-25 minutes on average. Some dives as long as two hours have been recorded! The first recordings showed the females averaging dives of 1093 feet, with a maximum depth of 2933 feet recorded in 2013. Male dives averaged 1148 to 1476 feet with maximum depths of 4373 to 5016 feet. Only about three minutes were spent at the surface between dives.

Elephant seals have many adaptations for life at sea, such as streamlined bodies that slice through the water, hind flippers that propel them and a thick layer of blubber (fat) that helps them conserve heat in the cold ocean depths. Their huge size also helps, females reaching 880 to 1980 pounds and eight to 11 feet in length and males reaching 3,300 to 5,100 pounds and 13 to 16 feet. They consume their prey whole so they don’t have to swallow a lot of water while chewing. Their large eyes to help them see underwater but their modified internal ear bones are their most important underwater sense. They focus sound and help determine its direction. (To us humans, underwater sound seems to come from all around.) They have very sensitive whiskers with more nerve endings per follicle to help detect vibrations underwater (like movement of their prey). 

Adaptations for deep dives are even more fascinating. With a rib cage more parallel to their backbones, their lungs can collapse on deep dives. This keeps them from developing “the bends” (nitrogen bubbles in their blood stream), which human divers can get if they are not careful.  Elephant seals have two times the volume of blood as land mammals their size and it’s fifty percent richer in hemoglobin, the chemical that carries oxygen to the cells. They can also slow their heartbeat when diving (from 55-120 beats per minute to 4-15 beats). This reduces blood flow and oxygen use (which can drop by one third). They also have a higher tolerance for carbon dioxide than humans do. They store extra-oxygenated red blood cells in their spleen to use as needed during deep dives and they reduce blood circulation to their extremities, concentrating it in their vital organs, where they need it most. 

We almost lost these astounding animals when they were hunted to near extinction from the late 1700s through the early 1800s. A small colony of 20 to 100 survived, hidden on remote Guadalupe Island in Mexico. Thanks to a ban on hunting and other protections, their population has rebounded to between 150,000 and 240,000. The seals have returned to most of their former range in the eastern Pacific, from the seas off the southern coast of Alaska through Baja California in Mexico. They have one of the longest migrations of any mammal: 11,200 miles for females and 13,000 miles for males.

Elephant seals have established rookeries (designated places for hauling out to breed, raise their pups and molt) where they are assured of finding a mate and a safe place to raise their young. Most northern elephant seal rookeries are on offshore islands or remote beaches in California and Baja, like Santa Barbara Island and Piedras Blancas Light Station on the Central California coast.

 A Year in the Life — the Land Life — of the Northern Elephant Seal.

November: Males arrive first at the rookery and establish their territories—the biggest and strongest bulls have a “harem” of as many as thirty females. They fast while on land, up to ninety days during breeding season. 

Mid-December: Females come ashore and give birth six to eight days later—by late January most births have occurred.

Through February: Pups are weaned after four weeks of drinking their mother’s milk and the females mate. The females, who have been fasting while on land, return to sea to hunt. Delayed implantation of the embryo allows the next birth to be timed for the female’s return to the rookery the following December. 

Between March and May: The pups slowly teach themselves to swim and hunt, sustained on the fat stored from their mother’s rich milk, then they head out to sea as well. 

May: Females return to molt.

July and August: The adult males arrive to molt as the females leave.

Late October: Juvenile haul out

Maybe you can plan a hike near one of the rookeries during a haul out event of interest to you. I hope you get a chance to see these amazing marine mammals soon.

Resources:

marinemammalcare.org

For an up close and personal view, visit the Marine Mammal Care Center in San Pedro in late spring/early summer when they may be treating injured or abandoned northern elephant seal pups.  

fisheries.noaa.govhttp://fisheries.noaa.gov

Look up the northern elephant seal to learn more

Vocalizations of the northern elephant seal at Piedras Blancas in this interesting video