Steller sea lions have attracted considerable attention in recent decades, both from scientists and the general public, due to significant (and largely unexplained) declines in their numbers over an extensive portion of their northern range, notably in Alaska.

Steller sea lion pups are born almost black, weighing around 23 kg (51 lb), and remain dark in coloration for several months.

[8][9][10] Males are further distinguished from females by broader and higher foreheads, flatter snouts, and a thick mane of coarse hair[11] around their large necks.

Based on genetic anаlyses and local migration patterns, the global Steller sea lion population has traditionally been divided into an eastern and western stock at 144°W longitude, roughly through the middle of the Gulf of Alaska.

[2][14] The oldest fossil known of the species was found near Kanazawa, Japan and dates to the late Early Pleistocene, approximately 800,000 years ago.

[1] Steller sea lions tend to live in the coastal waters of the subarctic because of the cooler temperate climate of the area.

[15] Typically, Steller sea lions spend their time in the water feeding but haul-out onto land to reproduce, raise their pups, molt, and rest.

[17] Steller sea lions are skilled and opportunistic marine predators, feeding on a wide range of fish and cephalopod species.

Important diet components include walleye pollock,[18][19] Atka mackerel,[18] halibut,[19] herring, capelin,[20] flatfish[20][21] Pacific cod,[18][19] rockfish,[20][21] sculpins,[20] salmon, sand lance, and cephalopods such as various squid and octopus.

The composition of the diet of Steller sea lions varies seasonally and geographically; as opportunistic predators, they concentrate on the locally most abundant prey species.

A week or so later, adult females arrive, accompanied occasionally by sexually immature offspring, and form fluid aggregations throughout the rookery.

Though researchers are uncertain as to the motives or reasons behind said attacks, it is suggested that the bull involved may have an abnormal personality akin to being psychotic.

A study conducted by the University of California, Santa Cruz found that on average male pups consume more milk than females.

As the pups matured, specifically at the sixth week past birth, the mother's sea time declined by 30 percent.

[31] A 2007 study of Steller sea lions found that a majority of thrust was produced during the drive phase of the fore flipper stroke cycle.

Using criteria based on velocity and the minimum radius of turns, Steller sea lions' maneuverability is similar to that of other eared seals, superior to that of cetaceans, and inferior to that of many fish.

[32] To be able to dive for a long period of time, Steller sea lions exhibit apnea, bradycardia, and peripheral vasoconstriction.

Mature male sea lions have a range of vocalizations as part of their territorial behaviors, including belches, growls, snorts, and hisses that serve as warnings to others.

Sonogram readings reported that Steller Sea Lions make discrete, low frequency pulses underwater that resemble the male "belching" territorial noise made in air.

[37] Vocalizations are critical to mother-pup pairs, as the mothers must find their pups in a crowded breeding area when they return from foraging.

[2] Killing sea lions is strictly prohibited in the US and Russia; however, in Japan, a fixed number are still harvested annually, ostensibly to protect their fisheries.

[41] In recent years, Steller sea lions have been known to enter the Columbia River estuary and feed on white sturgeon, several salmon species, and rainbow trout, some of which are also listed under the U.S.

[43] Though not as abundant as the California sea lion, there is still concern amongst agencies tasked with managing and monitoring the fish populations; as the Steller sea lions are, themselves, protected under the Marine Mammal Protection Act,[2] managers are implored to use non-harmful, non-lethal deterrence methods (such as rubber bullets, bullhorns and other noisemakers).

Additionally, the massive size of the Steller sea lion—and potential for aggression—poses a real threat for humans; thus, the interfering with, molestation or frightening of marine mammals is strictly forbidden.

This stems largely from the "junk-food hypothesis" representing a shift in their diet from fatty herring and capelin to leaner fare such as pollock and flounder, thereby limiting their ability to consume and store fat.

In females specifically, obtaining an insufficient amount of nutrients has resulted in the failure to complete their pregnancies to full term.