Steller Sea Lion

Stellers are the largest of all sea lions and they have an appetite to match. These giant pinnipeds hunt fish, squid, octopus, sea otters and, rarely, smaller seals. They are found off northern Pacific coasts from Japan to California.

## Description

Adult animals are lighter in color than most sea lions, ranging from pale yellow to tawny and occasionally reddish. Steller sea lion pups are born almost black, weighing around 23 kg (51 lb), and remain dark for several months. Females and males both grow rapidly until the fifth year, after which female growth slows considerably. Adult females measure 2.3–2.9 m (7.5–9.5 ft) in length, with an average of 2.5 m (8.2 ft), and weigh 240–350 kg (530–770 lb), with an average of 263 kg (580 lb). Males continue to grow until their secondary sexual traits appear in their fifth to eighth year. Males are slightly longer than the females; they grow to about 2.82–3.25 m (9.3–10.7 ft) long, with an average of 3 m (9.8 ft). Males have much wider chests, necks, and general forebody structure and weigh 450–1,120 kg (990–2,470 lb), with an average of 544 kg (1,199 lb). Males are further distinguished from females by broader, higher foreheads, flatter snouts, and darker, slightly tuftier hair around their large necks, giving them a maned appearance. Indeed, their Latin name translates roughly as "maned one with the broad forehead".

## Reproductive Behavior and Life History

Steller sea lion breeding is one of nature's great mass spectacles. When these giants thunder ashore, their favored beaches, called rookeries, disappear under their numbers. Young pups are sometimes crushed by the throng, unheeded by powerful males with only a single purpose in mind. Bulls (males) must establish and hold a beach territory in order to breed. Most do not achieve this until they are nine or ten years of age. Females begin to reproduce at about five years of age and typically have one pup per year. Sea lion mothers care for their young and recognize them by a keen sense of smell. Females slip into the sea to hunt and return to their young with the day's catch—identifying their own offspring by touch and scent. These animals are social and also gather at various times throughout the year when mating and breeding are not taking place. Even in crowds, the big bulls are unmistakable—they are three times larger than females.

### **Recent Decline and Subsequent Recovery**

While the populations of the eastern and Asian stocks appear stable, the population of the western stock, particularly along the Aleutian Islands, was estimated to have fallen by 70–80% since the 1970s. As a consequence, in 1997, the western stock of Steller sea lions was listed as endangered and the eastern stock was listed as threatened under the Endangered Species Act. They have since been the object of intense study and the focus of much political and scientific debate in Alaska.

One suspected cause of their precipitous decline was overfishing of Alaska pollock, herring, and other fish stocks in the Gulf of Alaska. 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. Other hypotheses include increased predation by orcas and sharks, indirect effects of prey species composition shifts due to changes in climate, effects of disease or contaminants, shooting by fishermen, and others. The decline is certainly due to a complex of interrelated factors which have yet to be defined by the research effort. In October 2013, the eastern Steller sea lion was taken off the U.S. Endangered Species List after a major population comeback over the past several years.