Hooker’s sea lions, also known as New Zealand sea lions, are one of only five species of sea lions in the world, the others being the Australian sea lion, the South American sea lion, the California sea lion and Steller sea lion.
Physical description and related species
Adult male sea lions can weigh over 400 kg and will aggressively defend harems of up to about 25 females from other males during the breeding season. Females weigh 85–160 kg and pups weigh 7–8 kg at birth.
Distribution and abundance
Hooker’s sea lions are one of the most regionally localized and rare of the world’s seal species. They breed almost exclusively at the Auckland Islands in the New Zealand subantarctic region. A few sea lions also breed on New Zealand’s Campbell Island.
Female Hooker’s sea lions tend to stay reasonably close to their breeding locations, but males range further afield. Each year some male sea lions are seen on Macquarie Island, which is the only Australian territory within this species range.
Threats: The total population is estimated to be only about 12 500 animals. Historically, this species’ range also included most of the New Zealand coast, but a combination of subsistence hunting by Maori and commercial sealing by Europeans reduced the range and numbers to the present extent. The population appears to have been stable for about the past five decades.
Each year some Hooker’s sea lions are drowned accidentally by fishing boats that trawl for squid around the Auckland Islands. The New Zealand Government has set a limit of 6080 sea lion mortalities per year in this fishery (based on a mathematical model), and the fishery has been closed early several times during the 1990s as this
limit was exceeded.
Conservation status: vulnerable
Pups are born in December and January each summer and are suckled for up to ten months.
Diet and feeding
Hooker’s sea lions feed on, or near, the seabed on a wide variety of prey including octopus, squid and several types of fish. They will occasionally feed on pelagic schooling crustaceans like lobster krill, and even on sea birds and fur seals. Large males have been seen killing and eating young elephant seals at Campbell Islands.
Special adaptations: Hooker’s sea lions can dive deeper and longer than any other of the world’s sea lion or fur seals. Although most feeding is done in waters of 100–200 m, with each dive lasting 3–6 minutes, some sea lions have been recorded to dive to over 600 m with dives of over 12 minutes.
The diving performance of this species is at the limit of their physical ability. They achieve such amazing depths by swimming fast in the first part of the dive and then by gliding down to the seabed, keeping very still to conserve energy and oxygen.