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The Steller sea lion is the largest member of the sea lion family. It has a massive body, a broad chest and features something resembling a mane of hair. Its coat is reddish-brown in colour. It has a large head and a flattened muzzle.
Males: up to 3.3 m and 1000 kg, mature between 3 and 7 years old. However, they are only able to defend their territory when they are about 9 years old.
Females: up to 2.5 m and 300 kg, mature between 3 and 6 years old.
At birth: 1 m and 20 kg, weaned around 1 year although nursing can last longer.
Longevity: 30 years for females and 20 years for males.
The Steller sea lion is the largest of the 16 species of sea lions.
The Steller sea lion lives throughout the North Pacific. There are two populations: the eastern population and the western population. The eastern population extends from mid-California to southeast Alaska. The western population lives in the Gulf of Alaska, the Bering Sea and extends to northern Japan.
Steller sea lions make use of the rocky coastline where they come to rest, mate and give birth. This living space is known as the rockery. In the sea, they can be found between the tidal zone and the edge of the continental shelf, areas in which they are particularly fond of hunting.
Their sexual dimorphism is very pronounced. The species is polygamous and, as adults, the male can be three times the weight of the female. It arrives before the females on the beaches. It is only from the age of 9 that the male is able to defend his territory and mate. The mating season is between late spring and early summer. Gestation lasts one year, taking into account a delayed implantation period of about 3 months. This is a period during which the female is fertilised but the embryo does not develop. If the mother has the right conditions (good nutrition, no illness), the foetus will develop. The single pup is born between May and July. The mother then stays on land for 7 to 10 weeks without leaving her pup, so that she can nurse it frequently, after which she begins to move away for periods of 18 to 25 hours. She is fertile again 2 weeks after giving birth.
Although they can travel long distances, Steller sea lions are not considered migratory. Only the young animals travel long distances and move away from the rockery. The adults tend to be somewhat sedentary.
Steller sea lions eat mainly fish and cephalopods but may sometimes feed on smaller sea lion species or seal pups.
As opportunists, they learned to feed from fishing nets which led to them being killed very regularly and in large numbers between the 1950s and 1970s.
The hunting behaviour of the female is different between summer and winter. In winter, she hunts further and deeper than in summer when she stays close to the rockery to nurse her pup.
The Eastern population:
There were heavy culling campaigns between the 1950s and 1960s which were then reduced around the 1970s. Although some animals are still killed by fishermen seeking to protect their catch, this practice has greatly diminished, especially since the authorities in the United States and Canada have completely banned the killing of this species. Since the 1970s, the population has slowly begun to increase again.
The Western population:
This population has declined by 70-80% since the 1970s. A number of possibilities for this have been considered, including culling by fishermen, accidental entanglement in fishing nets, disease, pollution and a decrease in food resources. According to recent studies, these various environmental factors, in addition to predation by killer whales, are putting pressure on the population. Since 2000, the population has increased somewhat indicating that some of these factors may be exerting less pressure.
Killer whales, some sharks and humans.
Reduce pressure on Steller sea lion food resources by eating fish from sustainable fishing.
Just before the mating season, the male will eat a lot to reach a weight of nearly 1000 kg. This weight will allow him to fast during the mating season. Thus, he will not go back to the water to feed and will be able to fiercely defend his beach and his harem against the advances of other males living around the edges.