Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition.

As they develop, both juveniles and adults go through a molting period in which their initially black fur is replaced with a coat that ranges from silver to deep grey, finally fading to tan.

The width of the eyes and a high concentration of low-light pigments suggest sight plays an important role in the capture of prey.

[citation needed] While their hind limbs are unfit for locomotion on land, elephant seals use their fins as support to propel their bodies.

They are able to propel themselves quickly — as fast as 8 kilometres per hour (4.3 kn; 5.0 mph) — in this way for short-distance travel, to return to water, catch up with a female or chase an intruder.

[citation needed] A unique characteristic of the northern elephant seal is that it has developed the ability to store oxygenated red blood cells within its spleen.

This fluid-filled structure is initially expanded due to the rush of RBC from the spleen and slowly releases the red blood cells into the circulatory system via a muscular vena caval sphincter found on the cranial aspect of the diaphragm.

This ability to slowly introduce RBC into the blood stream is likely to prevent any harmful effects caused by a rapid increase in hematocrit.

When the males leave their rookeries, they migrate northwards to their feeding grounds along the continental shelf from Washington to the western Aleutians in Alaska.

[15] When the females leave their rookeries, they head north or west into open ocean, and forage across a large area in the northeastern Pacific.

[17] Historical occurrences of elephant seal presence, residential or occasional, in western North Pacific are fairly unknown.

There have been two records of vagrants visiting to Japanese coasts; a male on Niijima in 1989[18] and a young seal on beaches in Hasama, Tateyama in 2001.

[19] A 2.5-metre (8 ft 2 in) female was found on Sanze beach, Tsuruoka, Yamagata in October 2017, making it the first record from Sea of Japan.

Certain individuals established haul-out sites at the Commander Islands in the early 2000s; however, due to aggressive interactions with local Steller sea lions, long-term colonization is not expected.

[23][15] Female elephant seals have been tagged and found to dive almost continuously for 20 hours or more a day, mostly in 400-to-600-metre (1,310 to 1,970 ft) deep water, where small fish are abundant.

[24] Northern elephant seals eat a variety of prey, including mesopelagic fish such as myctophids, deep-water squid, Pacific hake, pelagic crustaceans, relatively small sharks, rays, and ratfish.

[25][16][26] Octopoteuthis deletron squid are a common prey item, one study found this species in the stomachs of 58% of individuals sampled off the coast of California.

[27] A female northern elephant seal was documented in 2013 by a deep sea camera at a depth of 894 m (2,933 ft), where she consumed a Pacific hagfish, slurping it up from the ocean floor.

Elephant seals do not have a developed a system of echolocation in the manner of cetaceans, but their vibrissae, which are sensitive to vibrations, are assumed to play a role in search of food.

The shark, when hunting adults, is most likely to ambush a seal with a damaging bite and wait until it is weakened by blood loss to finish the kill.

[31] While fights are not usually to the death, they are brutal and often with significant bloodshed and injury; however, in many cases of mismatched opponents, the younger, less capable males are simply chased away, often to upland dunes.

[1] In 1874, Charles Melville Scammon recorded in Marine Mammals of the Northwestern Coast of America, that an 18-foot (5.5 m) long bull caught on Santa Barbara Island yielded 210 US gallons (795 L; 175 imp gal) of oil.

[40] They were thought to be extinct in 1884 until a remnant population of eight individuals was discovered on Guadalupe Island in 1892 by a Smithsonian expedition, who promptly killed several for their collections.

[42][43] Nevertheless, a genetic bottleneck experienced by northern elephant seals during the nineteenth century made them more susceptible to disease, environmental changes and pollution.

[46] Such issues from the bottleneck a sharp loss of genetic diversity and increased homozygosity in the surviving population, and also a decreased number of haplogroups.