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.

A Northward Spread In The Breeding Distribution Of The New Zealand Sea Lion (Phocartos Hooeri)

“…Continual sightings of identified migrant males over several years have indicated that the majority become resident at Otago (McConkey et al 2002a). Three of six identified migrant females at Otago were also seen regularly over several years though only one has produced any pups.…”

“…Juvenile males form the vanguard of dispersion among polygynous mammals (Dobson 1982). Otago is the northern-most site with year round presence of P. hookeri (McConkey et al 2002a). Through the five years 1995 -1999, 113 migrant males and four migrant females were identified at Otago (McConkey et al 2002a).…”

“…Otago is the northern-most site with year round presence of P. hookeri (McConkey et al 2002a). Through the five years 1995 -1999, 113 migrant males and four migrant females were identified at Otago (McConkey et al 2002a). This demonstrates that males predominate at the northern edge of distribution of the species.…”

“…Otago, in the southeast of the South Island, now marks the northern limit of year round presence by P. hookeri (McConkey et al 2002a). Residence has been demonstrated by repeat sightings of identified immigrant males over several years (McConkey et al 2002a).…”

“…Residence has been demonstrated by repeat sightings of identified immigrant males over several years (McConkey et al 2002a). The population estimate for immigrant P. hookeri at Otago in 1999 was 108 males and three females (McConkey et al 2002a). In this paper we document the recent initiation of breeding by P. hookeri at Otago.…”