New Zealand Sea Lion(Phocarctos hookeri)
They are one of the largest New Zealand animals. They have marked sexual dimorphism; adult males are 240–350 cm long and weigh 320–450 kg, while adult females are 180–200 cm long and weigh 90–165 kg. At birth, pups are 70–100 cm long and weigh 7–8 kg; the natal pelage is a thick coat of dark brown hair that becomes dark grey with cream markings on the top of the head, nose, tail and at the base of the flippers. Adult females' coats vary from buff to creamy grey with darker pigmentation around the muzzle and the flippers. Adult males are blackish-brown with a well-developed black mane of coarse hair reaching the shoulders.
Habitat
The main breeding populations are at the Auckland and Campbell Islands in the NZ Subantarctic, where approximately 99% of the species' annual pup production occurs. There are currently three functioning breeding rookeries on the Auckland Islands. Most sea lions are born on Dundas Island. A smaller rookery exists at Sandy Bay on Enderby Island and the smallest rookery is on Figure of Eight Island. An even smaller rookery at South East Point on Auckland Island appears to now have been abandoned.
The other major breeding area is the Campbell Islands.
For the first time in 150 years, sea lions began breeding again on the South Island coast in 1994, on the Otago Peninsula. Other small populations of breeding sea lions have recently begun to establish in various parts of the Stewart Island coastline and have been observed on the Catlins coast south of the Clutha River.
Diet
New Zealand sea lions are known to prey on a wide range of species including fish such as Antarctic horsefish and Patagonian toothfish, cephalopods (e.g. New Zealand arrow squid and yellow octopus), crustaceans, seabirds and other marine mammals, and even New Zealand fur seals. Studies indicate a strong location effect on diet, with almost no overlap in prey species comparing sea lions at Otago Peninsula and Campbell Island, at the north and south extents of the species' breeding range. New Zealand sea lions are in turn preyed on by great white sharks, with 27% showing evidence of scarring from near-miss shark attacks in an opportunistic study of adult NZ sea lions at Sandy Bay, Enderby Island.
Breeding
Males become sexually mature at the age of five years. The age of maturity for females is 3-4 years. The average estimated reproductive rate of adult female New Zealand Sea Lions is 65% per year. Pup mortality at the end of one year was 30-55% for the Auckland Islands area, and pup mortality was 55% for the first 6 weeks after birth at Campbell Island. Males live at least 23 years and females to at least 26 years. The breeding season for the New Zealand Sea Lion 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 on average within 2.1 days 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 neighbours, and turn-over of males is a regular occurrence. Many territorial bulls depart the rookery in mid-January with the end of the pupping period. The onset of oestrous occurs 7-10 days after a female gives birth. Prior to this, females continuously attend their newborn pup. Following mating, females begin a phase of short foraging trips followed by pup attendance, typical of many otariids. Foraging trips average 2.7 days and are followed by 1.5 days of pup attendance and feeding ashore. Pups gather into groups while their mothers are away. Pups are weaned at approximately 10 months. The primary causes of pup deaths within the first two months of life are trauma (35%), bacterial infections (24%), hookworm infection (13%), starvation (13%), and stillbirth (4%). Adult males are a source of mortality to pups, occasionally trampling them during territorial disputes and also through incidents of cannibalism.
Population
According to the IUCN Red List, they are classed as Endangered(EN). New Zealand Sea Lion pups are estimated to account for 65% of the total number of mature females, and additional to this it has been estimated that 20% of all mature females will never breed. In 2008-09 New Zealand Sea Lions numbered approximately 9,880 (95% CI, 8,604–11,297) based on total pup production of 2,084, with the number of mature individuals estimated as less than 3,000. Using 2013/14 data indicating total pup production of 2,189, the number of mature individuals is estimated to be 3,031. The majority of pups are born at the Auckland Islands and annual pup production estimates have been made there since 1994/95. Estimates suggest that the population was largely stable until 1997/98, but has declined since then at a rate of 4%/year. The number of pups counted in 2013/14 was 18% less than in 2012/13, and 48% less than 1997/98. The decrease in pup production at Auckland Islands has been linked with decreasing numbers of adult females. The other location where a substantial number of pups are born is Campbell Island. Campbell Island is at the southern limit of the New Zealand Sea Lion range and pup mortality is very high there, apparently due to cold and wet conditions during the pupping season and substrates unsuitable for a breeding colony and early pup survival. A few pups are also born on the south coast of the South Island of New Zealand and on Stewart Island not far offshore. The pups born at Stewart Island were only discovered in 2010/2011 and since that year regular searches of the most likely places Sea Lions would pup have been undertaken. The apparent increasing trend of Stewart Island pup counts is an artefact of better search techniques and areas searched on Stewart Island since 2010/2011 rather than an increase in pup numbers. The number of pups born at those locations has been about 30/year, which is less than 1% of the total pup production.The mean age of reproduction for female New Zealand Sea Lions is 10.75 years hence the generation time is estimated to be 10.75 years with 3 generations being equivalent to approximately 32 years.
Threats
Commercial sealing in the early 19th century decimated the New Zealand Sea Lion population in the Auckland Islands, but despite the depletion sealing continued until the mid-20th century. The population has yet to fully recover from the period of overexploitation. At the present time, New Zealand Sea Lions have a highly restricted distribution, a small population, and nearly all of the breeding activity is concentrated in two subantarctic island groups. This restricted and small breeding population in combination makes them vulnerable to disease outbreaks, environmental change, and human activities.
The commercial Arrow Squid trawl fishery near the Auckland Islands reported their first New Zealand Sea Lion bycatch mortalities in 1978. Reported or estimated mortality between 1995 and 2007 averaged 92 animals annually (range 17-143) which was 3.7% of the estimated number of mature individuals in the Auckland Island area. Of particular concern is that most bycatch animals are females (up to 91%; Chilvers 2008). New Zealand Sea Lions are also incidentally caught in other trawl fisheries around the Auckland and Campbell Islands. Apart from direct mortality, competition and habitat modification caused by fishing activity may also be impacting New Zealand Sea Lion foraging areas. Epizootic outbreaks at the Auckland Islands in 1998, 2002, and 2003 led to more than 50%, 33%, and 21% early pup mortality respectively, and were also responsible for the deaths of some animals from other age classes during 1998. The source of the suspected bacterial agent and cause of the outbreak and subsequent mortality for the 1998 outbreak are unknown, however the 2002 and 2003 outbreaks have been identified as being caused by Klebsiella pneumoniae.
Conservation
The New Zealand government has provided protection to New Zealand Sea Lions with laws that date back to 1881. The Marine Mammal Protection Act of 1978 added additional measures, stating that no marine mammal could be caught, killed, injured, attracted, poisoned, tranquillized, herded, harassed, disturbed, or possessed. However, those measures do not afford protection from incidental captures in commercial fisheries if they are reported to the appropriate officials as required. The uninhabited Auckland Fauna Reserve forms part of the habitat of New Zealand Sea Lions. Tourism is regulated on islands and at some mainland beaches on the South Island. Due to the declining population, the New Zealand Sea Lion was listed as a Nationally Critical New Zealand Species in 2010 under the New Zealand threat classification system.
There are three main management strategies currently in place to mitigate New Zealand Sea Lion bycatch interactions in trawl fisheries off the Auckland Islands:
1) Input controls: a Marine Mammal Sanctuary and Marine Reserve surrounding the Auckland Islands extending 22.2 km offshore, within which no trawling or any other form of fishing is allowed. However, satellite tracking data indicate that this closure only protects a small part of the foraging areas of adult females.
2) Output controls: restrict the number of New Zealand Sea Lions the trawl fishery may kill incidentally within designated fishery management zones before the zone is closed for the season.
3) Sea Lion exclusion devices (SLEDs): SLEDs were introduced to the fishery in 2001. A SLED is a metal grid fixed inside the trawl net that allows smaller objects, such as squid, to pass into the cod-end, while larger objects are directed to an escape hatch opening. There is uncertainty about the efficacy of SLEDs and the overall impact of fishery interactions on New Zealand Sea Lion populations.