Steller Sea Lion(Eumetopias jubatus)
They are also known as Steller's sea lion and Northern sea lion. They are the biggest of all the sea lions. Adult are lighter in colour 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, and remain dark in coloration 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 in length, on average being 2.5 m, and weigh 240–350 kg, with an average of 263 kg. Males continue to grow until their secondary sexual traits appear in their fifth to eighth year. Males are slightly longer than the females, growing to about 2.82–3.25 m long and averaging 3 m in length. Males have much wider chests, necks, and general forebody structure. Males can weigh between 450–1,120 kg, weighing on average 544 kg. Males are further distinguished from females by broader and higher foreheads, flatter snouts, and a thick mane of coarse hair around their large necks.
Habitat
These sea lions inhabit the northern Californian coast, northwards to Alaska and on the coasts of Japan and Russia. They occur in the northern Pacific Ocean’s cool waters, hauling out on the rocky coastline and on beaches. In the summer, they tend to shift their range somewhat southward.
Diet
Steller sea lions are carnivores (piscivores, molluscivores), they mainly eat Atka mackerel, walleye pollock, Pacific cod, and Pacific salmon. They also eat octopus, squid, gastropods and bivalves. They also kill harbor seals, ringed seals, younger northern fur seals and other animals.
Breeding
Steller sea lions use a polygynous mating system. The only males allowed to mate are the dominant males; however, younger males will sneak into rookeries and attempt to mate with the females without the dominant male noticing. The dominant males will guard and mate with as many as 30 females in one mating season. Females give birth to a single pup between mid-May and July after a gestation period that lasts for approximately 12 months. Females care for their offspring for up to three years, nursing them for as long as a year, sometimes longer. Males are not much involved in parental care but will guard all of the females they have mated with. Both males and females reach maturity between three to six years of age. Due to competition with other males, most bulls are unlikely to successfully breed until eight or ten years of age.
Population
According to the IUCN Red List, the total Steller sea lion population size is approximately 160,867 individuals. This includes population numbers of two recognized populations of the species: Western Steller sea lion population-79,929 individuals, with 55,791 animals in the USA and 24,138 animals in Russia; Loughlin’s Steller sea lion population-approximately 80,938 individuals. Currently, Steller sea lions are classified as Near Threatened (NT), however, their numbers today are increasing.
Threats
Current threats to this species include: boat/ship strikes, illegal hunting/shooting, contaminants/pollutants, habitat degradation, offshore gas and oil exploration, interactions (indirect and direct) with fisheries, direct impacts largely because of fishing gear (set and drift gillnets, longlines, trawls, etc.) which can hook, entangle, injure, or kill them, and indirect impacts from competition for food, possible changes to critical habitat, etc.
Conservation
Western Steller Sea Lions are listed as vulnerable in the Threatened Wildlife of Japan Red Data Book. It was reported that over 200 Steller Sea Lions were culled annually between 1960-1993 to reduce predation on commercial fish stocks. Recent work indicates that the annual culling was then reduced to a limit of 116/year until 2010 at which time a new 5 year quota of 1,030 culled Sea Lions was imposed. This resulted in an increased annual average take. In 2015 approximately 400 Steller Sea Lions were reported to be culled in Japan. In Russia, the major Steller Sea Lion rookeries were given protection under the Northern Fur Seal and Sea Otter Conservation Act in the late 1950s. They were listed as endangered (category 2) in the Russian Red Data Book in 1994 and harvest was prohibited. These measures had a positive effect in the western portion of the range as the population increased around Sakhalin Island, the Kuril Islands, and in the northern Sea of Okhotsk. However, abundance along the eastern coast of Kamchatka and in the Commander Islands has not recovered for unknown reasons.
In the USA the Steller Sea Lion is listed as depleted under the US Marine Mammal Protection Act. The species was listed as threatened under the ESA in 1990, and in 1997 the western population was uplisted to endangered. A recovery plan for Steller Sea Lions was approved in 1992, and a revised recovery plan was published in 2008. Critical habitat was designated under the ESA in 1993. No-entry zones were established around rookeries at the time of listing, and fisheries, particularly those operating in critical habitat, have been managed to reduce the likelihood of competitive interactions. Substantial funding has been made available for Steller Sea Lion research to develop information on ecology, behavior, genetics, population dynamics, and movements. Results have been used to assist in the development of management activities, to attempt to understand the reasons for the decline, and to promote recovery of the species. The fact that the overall growth rate of the western population is now positive suggests that at least some of these conservation efforts have had a beneficial effect. A species status review conducted in 2013 found that the Loughlin’s Steller Sea Lion population increased more than 3% per year since the 1970s and therefore it was removed from the ESA threatened species list. The western population in the USA is still listed as endangered under the ESA.