|Habitat and Ecology:
Eumetopias jubatus are the largest otariids and the fourth largest pinniped. Both sexes are robust and powerfully built. They are sexually dimorphic, with adult males weighing three times as much, and growing 20–25% longer than, adult females. Pups are born with a thick blackish-brown lanugo that is moulted by about six months of age. The maximum length of adult males is about 3.3 m and average weight is 1,000 kg. The maximum length for adult females is about 2.5 m and average weight is 273 kg. Pups are born at an average size of about 1 m and 18–22 kg (Loughlin 2009).
The age of sexual maturity is 3–6 years for females, and 3–7 years for males (Calkins and Pitcher 1982). Males are not able to defend territories before they are nine years old. The reproductive rate of Loughlin’s Northern Sea Lions is unknown, but the pregnancy rate of mature female western Steller Sea Lions was found to have declined during the 1970s and 1980s and was estimated to be 55% in the 1980s (Pitcher et al. 1998). Gestation lasts one year, including a delay of implantation of about three months. Females may live to be up to 30 years old and males to about 20 years (Loughlin 2009).
Loughlin’s Northern Sea Lions are highly polygynous and breed in the late spring and summer. Adult males arrive before females and those that are nine years or older establish themselves on territories, which they aggressively defend. Pups are born from May through July, and females stay continuously ashore with their newborns for the first 7–10 days after giving birth. Following this period of attendance, females make foraging excursions, primarily at night for periods of 18–25 hours, followed by time ashore to nurse their pup. Females come into oestrus and mate about two weeks after giving birth. Weaning can occur before the next breeding season, but it is not unusual to see females nursing yearlings or older juveniles (Loughlin 2009).
Loughlin’s Northern Sea Lions are primarily found from the coast to the outer continental shelf and slope. They sometimes leave haulouts in very large groups; however, sightings at sea are most often of groups of 1–12 animals. They aggregate in areas of prey abundance, including near fishing vessels, where they will feed on netted fish and discarded by-catch. Loughlin’s Northern Sea Lions have been known to move westward into the range if the western Steller Sea Lion, and some juvenile males have crossed the Gulf of Alaska to near Kodiak Island. They are not considered migratory; juveniles and subadults make the longest distance trips. Adults usually forage and live near their natal colonies and return to these sites to breed. The area used by adult females for foraging in winter increases dramatically over the area used in the summer and females tend to dive deeper in winter than summer. Diving is generally to depths of 200 m or less (Loughlin et al. 2003, Rehberg and Burns 2008). Dive duration is usually two minutes or less, with both parameters varying by season and age of the animal. Diving ability of pups and juveniles increases with age, and they routinely dive to depths of around 140 m for periods of two minutes as yearlings. The diving of adult males has not been studied.
Loughlin’s Northern Sea Lions feed on many varieties of fish and invertebrates. Much of the information on diet comes from animals living in southeast Alaska, where they feed on Walleye Pollock, Pacific Cod, flatfishes, rockfishes, herring, salmon, sand lance, skates, squid, and octopus (Trites et al. 2007). Adult females with young pups feed extensively at night, switching to foraging at any time after the breeding season. Sea Lions have been reported to kill and consume Harbor Seals in Glacier Bay National Park, Alaska.
The primary predators of sea lions are Killer Whales (Loughlin 2009). Sleeper Sharks in Alaska have been found with Sea Lion remains in their stomachs, but it is unknown whether the prey was killed or scavenged. Great White Sharks presumably take young animals in areas where their range overlaps.