Pattern Of Immigration Of New Zealand Sea Lions Phocarctos Hookeri To Otago, New Zealand: Implications For Management

Abstract

The present management strategy for New Zealand sea lions Phocarctos hookeri assumes that kills in a squid trawl fishery around Auckland Islands, the species population base, have prevented an increase in abundance of sea lions. This strategy also assumes that emigration will be initiated as the population reaches carrying capacity, and that emigration rates will be density dependent. We used the combination of photographic identification of individuals and diagnostic features of age classes to estimate immigration rates of P. hookeri to Otago, South Island, New Zealand. Most immigrants were males = 2 years old at arrival, and included animals tagged as pups at Auckland Islands. Estimates for total numbers of immigrants to Otago from four consecutive cohorts, 1991/92 - 1994/95, varied three-fold through a period of constant annual pup production at Auckland Islands. The greatest influx was from the 1993/94 cohort, a breeding season that predated the enforcement of early closures of the squid fishery. We suggest published records from the Auckland Islands indicate that this population is already at carrying capacity. If so, then factors other than, or in addition to, pup production and fishery mortality have an impact on emigration rates.