Investigation of the 1998 mass mortality event in New Zealand sea lions

Abstract

The New Zealand (Hooker's) sea lion, Phocarctos hookeri, is New Zealand's only endemic pinniped, and, with a population of less than 15,000 (Gales and Fletcher 1999) and a limited breeding range, is one of the world's most endangered pinnipeds. While the range of the NZ sea lion extends from Macquarie Island in the south to the South Island of New Zealand in the north (Childerhouse and Gales 1998), breeding occurs in a much more restricted area. The main breeding sites are in the sub-Antarctic islands, with between 86% (Wilkinson et al. 2003) and 95% (Cawthorn 1993) of pups born at four breeding colonies in the Auckland Islands. A further breeding population is present on Campbell Island, and recent studies suggest that the importance of this colony is increasing (Childerhouse et al. 2005; Childerhouse and Gales 1998; Chilvers et al. unpublished data). Occasionally pups are born on Stewart Island (Childerhouse and Gales 1998) and the New Zealand mainland (McConkey et al. 2002). Currently, the NZ sea lion is classified as 'Vulnerable' by the International Union for Conservation of Nature (IUCN) (Reijnders et al. 1993), and as 'Threatened' under the New Zealand Marine Mammal Protection Act 1978 (Hitchmough 2002).