New Zealand Sea Lion - Phocarctos hookeri

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The Story: New Zealand sea lions, Phocarctos hookeri, are one of only 5 living sea lion species in the world, and they are the rarest! NZ sea lions total species population size is less than 10,000 animals and for their biggest breeding area, the Auckland Islands, the population is declining quickly. NZ sea lions used to live on all islands of NZ, both the North and South Island, however due to sealing in the 1900's they now only breed on the NZ sub-antarctic Islands, Auckland and Campbell islands. There are about 5 or 6 special females that also breed in the Otago area which are the first female NZ sea lions to breed on the NZ mainland in 200 years.

NZ sea lions are NZs largest endemic native animal. They are sexual dimorphic with an obvious difference in appearance between males and females. Males are much darker than females and weigh 350 to 500kg as adults while females are silver/blonde and have a mass of 100 - 140kg as adults. NZ sea lions can live to 20 years old, with females living longer

than males. Females can have their first pup at 4 to 6 years of age, while males are sexually mature at 6 to 7 years but are not big enough or assertive enough to hold a territory and therefore a harem, until they are 9 to 12 years old. NZ sea lions are polygamous breeders meaning one male holds a harem of up to 25 females. \

Mating and breeding occurs during summer each year. NZ sea lions are very site specific (philopatric), with females coming back to the same beach they were born at to breed. During the breeding season males arrive first in late November to fight and set up an area to defend before the females arrive in mid to late December. Females usually arrive 2 to 3 days before giving birth to a single pup. They then stay with their pups for 8 to 10 days before returning to sea for a short period to feed. For the next year, after the birth of her pup, the female spends her time split between being on shore feeding her pup and at sea foraging. During the 8 to 10 day period ashore after the birth of her pup, the female is mated by the territorial male and therefore becomes pregnant again for the following year.

Male Sea Lion with harem of female sea lions. Photo: Jo Hiscock.

Pups are born at between 8 to 12 kg and grow to 20 to 30kg within the first 6 weeks of life. To achieve this growth rate, females must feed their pups with high quality milk (about 20% fat in the milk). To be able to make this high quality milk, females must work very hard travelling up to 175km away from their pups and back again in a 2 day period. During these trips, females perform hundreds of dives, some of them reaching up to 700m in depth. Female NZ sea lions make foraging trips that are longer, further and deeper than any other sea lion in the world with their foraging behaviour thought to be at their physiological limit. NZ sea lions feed mainly on Rattail fish - Coelorinchus spp., Opal Fish - Hemerocoetes spp., arrow squid -Nototodarus sloani and octopus -Enteroctopus zealandicus.

While mums are away feeding, pups form puppy piles on the beach for protection and warmth. As pups get older their mums move them inland into grassy and forested areas for protection from the weather and from male sea lions which is a very unusual behaviour for a sea lion species.

Sea Lion pup with tag. Photo: Louise Chilvers.

Classification: Kingdom: Animalia. Phylum: Chordata. Class: Mammalia. Order: Carnivora. Family: Otariidae. Genus: Phocarctos. Species: hookeri. (Gray, 1844)

The Scientist: Dr. B. Louise Chilvers, Senior Research Officer, Massey University.

I was inspired to be a scientist because of my love of animals and the sea. The best job in the world is the one where you get to do what you love every day, working with animals in the wild, working in and around the sea, and helping conserve the animals and their habitat. My research is undertaken in and around NZ, particularly the NZ sub-antarctic Islands. It is a cold wet place - even in summer, but that is where these animals live and it is an amazing habitat that needs conserving.

While we are down in the sub-antarctic the main jobs we do every day are counting sea lions, undertaking re-sightings of animals tags, tagging pups (this involves picking up every pup on the beach and tagging them - this is really hard work as pups weigh between 8 and 18 kg) and necropsying every animal that dies on the beach to understand what are the main causes of natural mortality for NZ sea lions.

Louise at work on the Auckland Islands.

Useful Links:

http://www.massey.ac.nz/massey/learning/colleges/college-of-sciences/about/veterinary-and-animal-sciences/staff-list.cfm?stref=182350

http://www.doc.govt.nz/conservation/marine-and-coastal/other-marine-protection/auckland-islands/

http://www.teara.govt.nz/en/seals/page-6

The Sealion Video via YouTube, as produced by Hamish Hooper: https://www.youtube.com/watch?v=RsOnrgHllnk


Glossary:

Habitats: a habitat is a place or area that a plant or animal is naturally found. Examples of marine habitats include kelp forest, mangroves and sandy beach.

Necropsy: the examination of a body after death to help determine cause of death; similar autopsy.

Philopatric: is the tendency of an organism to stay in, or return to, its home area.

Sexual dimorphic: is the physical difference between males and females of the same species, ie colour, size, mass.