Threats to sea lion

New Zealand sea lions were exploited for their pelts for a period of 24 years following the discovery of the Auckland Islands in 1806. It is evident that many New Zealand sea lions were killed during this time but it is unknown exactly how many due to poor and often non-existent record keeping. This killing continued until the late 1880’s when the animals were protected by law.

The New Zealand sea lion is classified as “Vulnerable” by the IUCN. This means that it is believed that if causal factors continue to operate this species will likely move into the “Endangered” category in the near future.

A recent population estimate suggests the total population may be smaller than 12,000 and appears to be declining.

Predators

Sharks are predators of the New
Zealand sea lion

Sharks are the New Zealand sea lions most likely predators. This is based on presence of wounds consistent with these predators.

Human impact

Hunting by Polynesian settlers and European sealers led to the near extinction of New Zealand sea lions resulting in their disappearance from the mainland 200 years ago.

Modern threats include drowning in trawl fisheries, disease, human disturbance and predation.

Every year New Zealand sea lions drown due to accidental entanglement in trawl nets in the sub-Antarctic squid fishery. This fishery operates in the foraging area of the Auckland Islands shelf between February and May, coinciding with the first four months of sea lion lactation. With both New Zealand sea lions and trawlers targeting the same prey, accidental captures of sea lions are inevitable.

The impact of fisheries-related mortality on the New Zealand sea lion population is as yet unknown. There is some suggestion that this level of take may limit the capacity for population recovery and may even cause population decline.

The Ministry of Fisheries sets a maximum limit on sea lion deaths every season; if this limit is exceeded the fishery is closed for the season. DOC and  the Ministry of Fisheries are working with the fishing industry to limit this bycatch through improved fishing practices.

Uncertainty about human impacts on the population is heightened when considered in conjunction with natural regulators of population growth.

Over recent years, the New Zealand sea lion has been affected by three epidemics caused by bacterial infection. Most significantly, disaster struck this species in their Auckland Islands stronghold in the 1997-98 summer breeding season. More than half the season’s pups died as a result of a mysterious ailment, possibly a bacterial infection. Hundreds of adults were also estimated to have died. Disease is a serious risk for this species due to its highly restricted range.

People and dogs pose a threat to sea lions on the mainland. Pups are also threatened by predation from large sharks and even adult males of their own species.

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