New Zealand sea lions are large heavy-bodied sexually dimorphic animals. Adult males are 1.2-1.5 times longer and 3-4 times heavier than adult females. The head is large and blocky with a short, wide muzzle that is blunt to rounded on the end in both sexes. The ear pinnae are small and inconspicuous. The vibrissae are short to moderate in length, reaching as far back as the pinnae on some animals.
The head of adult males looks especially foreshortened as the neck widens rapidly behind the position of the ears, obscuring much of its length. Bulls have a strong sagittal crest well behind the eyes, creating a domed appearance to the crown and a downward slope to the end of the short muzzle with little or no discernable forehead. Depending on posture and viewing angle the silhouette of the head in some males appears slightly rounded-out from the crown to the end of the muzzle. Bulls have greatly enlarged wide, thick, rounded necks, increasing in size from the nape and throat to the shoulders. The large neck is covered in a mane of longer coarser guard hairs. The hindquarters are not as enlarged as the neck, but are heavy and powerfully-built. Females and subadults have a flat-topped head with a slight slope to the end of the short muzzle. Their stocky body lacks the enlarged neck and longer guard hairs of the mane.
Pups are born in a thick long lanugo and are dark brown with a lighter crown, nape, and mystacial area, and a pale stripe on the top of the muzzle, originating on the crown. Female pups are lighter than male pups. Pups begin to molt their birth coat at 2 months and at the end of the molt look like adult females. Adult females and juveniles of both sexes are buff to creamy or silvery gray above and light tan to pale yellow below. The diffuse demarcation between light and dark is high on the neck and usually extends over the insertion of the fore flippers, and is lower on the sides of the abdomen. There is considerable subtle variation in the coloration of the head and muzzle. The light coloration often extends above the ears, which can appear highlighted with light color, above the eyes, and down the sides of the muzzle. The crown and top of the muzzle are usually darker. The area around the insertion of the fore flippers and the tops of the flippers is often darker grayish to light brown. In some adult females there may be little discernable contrast between coloration above and below, especially when they are faded just before they molt.
Males darken as they mature, and pass through a sequence of color phases before becoming fully dark blackish-brown as adults. From 1-3 years old they look like females, although some are light rusty brown. At 4 years old they become darker brown above, but remain pale yellow to light brown, below. They also begin to show increased bulk in the neck and shoulders and signs of a mane at this age. At 5-6 years old, their coloration and body shape is that of the adult male and they are blackish brown over the entire body. Physical maturity is reached in the 7th year. Some older males have white hairs in the mane, giving them a subtle grizzled appearance. From 2 years old, New Zealand sea lions go through an annual molt that lasts approximately 2 months and can occur anytime between December and June. One-year olds only experience a partial molt.
The fore flippers have a sparse short fur that extends beyond the wrist onto the middle of the dorsal surface of the flipper in a “V” pattern that does not reach the rounded tip. The rest of the dorsal surface, and the palms of both fore flippers are covered with a hairless black leathery skin. The first digit is the longest, widest and thickest, and curves posteriorly, giving the flipper a swept back look. Digits 2-4 are successively shorter. There is a small opening in the skin at the end of each digit for a claw that is usually reduced to a vestigial nodule, and rarely emerges above the skin. The claw openings are set back from the free edge of the flippers by cartilaginous rods that extend the length of each digit, and expand the size of the flippers. The hind flippers also have cartilaginous rods that extend the length of each toe. The bones of the three central toes terminate at the position of the small nails that emerge through the skin on the dorsal surface, set back from the end of the flipper. The first and fifth toes are longer than the three middle toes, and the first toe, or hallux, is longer and wider than the fifth toe. The hind flippers have short hair covering part of the proximal end of the flipper, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin.
Minimal information on the size of adult males is available. Adult males are 2.3-2.7 m long and may weigh from 320-450 kg, although these values might be high in the light of recent information that males are probably shorter than previously reported. Adult females are 1.8-2 m long and weigh 90-165 kg. Newborns are approximately 70-100 cm long and weigh 7-8 kg.
The dental formula is I 3/2, C 1/1, PC 6/5.
Can be Confused With
Three fur seals (New Zealand, Antarctic, and sub-Antarctic) are known to occur in or near the present range of the New Zealand sea lion. New Zealand sea lions can be differentiated from all fur seals, based on a combination of features including coloration, fur characteristics, head and muzzle shape, size of the ear pinnae, and size and shape of the outer toes on the hind flippers.
The primary habitat of New Zealand sea lions is several sub-Antarctic islands south of New Zealand, and their surrounding waters. The principal breeding colonies accounting for 95% of annual births are in the Auckland Islands, with smaller numbers breeding at Campbell Island and the Snares Islands. New Zealand sea lions regularly occur in small numbers at Stewart Island and on the southeast coast of the South Island of New Zealand, and there are occasional births. However, most of these animals are males ranging from 2-11 years old. Wandering New Zealand sea lions also reach Macquarie Island. Historically, New Zealand sea lions had a more extensive range that appears to have included most of New Zealand.
Ecology and Behavior
The breeding season for New Zealand seal lions begins in late November when adult males return and establish themselves on territories through displays, vocalizing, and fighting. Adult females arrive in early December and give birth shortly after returning to the rookery. Males may have as many as 25 females within their territories. The bulls are frequently challenged by newly arriving males and neighbors, and turn-over of males is a regular occurrence. Many territorial bulls depart in mid-January with the end of the pupping period.
The onset of estrous occurs 7-10 days after a female gives birth. Prior to this she continuously attends her newborn pup. Following mating, females begin a phase of short foraging trips followed by pup attendance, typical of many otariids. Foraging trips average 1.7 days and are followed by 1.2 days of pup attendance and feeding ashore. Also typical of many otariids, pups gather into groups while their mothers are away. Females and pups recognize each other through vocalizations and scent, and a small percentage of females will allow additional pups to nurse along with their own pup, which is unusual behavior for a pinniped. Pups are weaned at approximately 10 months. Adult males are a significant source of mortality to pups, occasionally killing them outright, and also through incidents of cannibalism. Pups are also trampled and killed by adult males challenging other males during territorial disputes.
New Zealand sea lions do not appear to be migratory, although they disperse widely over their range during the non-breeding season. Some animals can be found at major rookeries and haul-outs year-round. At sea they are active divers that forage on benthic prey. Mean dives are to 123 m and mean duration is 3.9 minutes. Maximum dive depths are over 500 m and dives have been recorded to last as long as 11.3 minutes. Predators include sharks, leopard seals, and presumably killer whales.
Feeding and Prey
New Zealand sea lions take a wide variety of vertebrate and invertebrate prey. Frequently-taken species include: opalfish, octopus, munida, hoki, oblique-banded rattail fish, salps, squid and crustaceans. Prey is taken in both benthic and pelagic habitats. Antarctic, sub-Antarctic, and New Zealand fur seals are taken as prey by adult male sea lions. Penguins and sea lion pups are also occasionally taken.
Threats and Status
New Zealand sea lions once were more abundant, with a much more extensive range that included the North and South islands of New Zealand. The Maori people of New Zealand traditionally hunted sea lions, as did Europeans upon their arrival. Commercial sealing in the early 19th century decimated the population in the Auckland Islands, but sealing continued until the mid-20th century, when it was halted. The population has yet to fully recover from this period of overexploitation.
At the present time, New Zealand sea lions have a highly restricted distribution, a small population that numbers approximately 12,500 animals, and most of their breeding is concentrated in one island group. This combination makes them vulnerable to disease outbreaks, environmental change, and human activities.
Commercial fisheries around the main sea lion population concentration in the Auckland Islands has resulted in sea lion mortalities through drownings. The New Zealand government has responded with a variety of management actions that are aimed at documenting, reducing, and limiting the annual incidental take of sea lions. Tourism at mainland sites and remote sub-Antarctic islands can cause disruption to haul-out patterns and breeding activities, and is regulated.
An epizootic outbreak in the Auckland Islands in 1998 led to more than 50% pup mortality, and also claimed the lives of many animals from other age classes. The source of the suspected bacterial agent and cause of the outbreak and subsequent mortality are unknown, but may have been triggered by El Niño-related food shortages stressing the population.
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