The Inter-Island Translocation of the New Zealand Frog Leiopelma Hamiltoni

The inter-island translocation of the New Zealand frog Leiopelma hamiltoni

Mandy D. Tocher1,2, Shirley Pledger3

1 Science and Research Unit, Science Technology and Information Services, Department of Conservation, Private Bag 1930, Dunedin, New Zealand 2 Corresponding author; e-mail: [email protected] 3 School of Mathematical and Computing Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand

Abstract. Leiopelma hamiltoni from Maud Island, Marlborough Sounds, New Zealand is conﬁned to two populations totalling approximately 19,000 individuals. In May 1997, 300 L. hamiltoni from Maud Island were translocated to nearby Motuara Island in an effort to expand their distribution and lower the risk of extinction for the species. By August 2002, 155 of the translocated frogs had been recaptured and the population contained a range of young to old frogs. Population estimates indicated the population on Motuara Island had stabilised with losses of the translocated frogs offset by new recruits. The ﬁrst juvenile frog was found in January 1998, only 10 months after the translocation and 42 recruits were captured by August 2002. Although initial survival was low for the translocated frogs, survival following the initial 2-month settling-in period was high (71-100%). New recruits produced on Motuara Island had survival rates of 29-88%. Capture-recapture analyses support the view that the survival estimates include a large dispersal component. The a priori criteria for a successful translocation were met; the appropriateness of the Motuara Island habitat for breeding and adult survival was demonstrated.

Key words: Capture-recapture; conservation management; Leiopelma; New Zealand; translocation.

Introduction The Maud Island frog Leiopelma hamiltoni (sensu Holyoake et al., 2001) is a threatened frog species that, prior to the translocation outlined in this report, existed as two populations on Maud Island, Marlborough Sounds, South Island, New Zealand (Bell and Bell, 1994; Newman, 1996; Bell et al., 2004; fig. 1). The Maud Island frog is considered to be an evolutionary significant unit based upon its genetic and geographical differentiation from L. hamiltoni from nearby Stephens Island, an off-shore Island in the Cook Strait (Holyoake et al., 2001; fig. 1).

Figure 1. Locality map showing Maud Island and Motuara Island, Marlborough Sounds, South Island, New Zealand.

The total population size of the Maud Island frog has been estimated at 19,000 individuals (Bell and Bell, 1994; Bell, 1995a). Using the IUCN Red Data Book categories, Bell (1994) suggested that the Maud Island frog should be classiﬁed as “vulnerable” because of their restricted area of occupancy and the small number of locations that they inhabit. In New Zealand, the Maud Island frog is considered “nationally endangered” and as such is subject to a recovery plan (Newman, 1996). The Maud Island frog probably inhabited a much larger area, including the mainland adjacent to Maud Island (Worthy, 1987a, b). Sub fossil remains of “L. hamiltoni” have been recorded from caves over the west and north-west of the South Island (Worthy, 1987a, b). As with most New Zealand fauna, the arrival of humans and various mammalian predators are the likely cause of the reduction in the distribution of the Maud Island frog to a single predator-free island (Newman, 1996). One objective of the New Zealand Native Frog Leiopelma spp. Recovery Plan is to establish another population of the Maud Island frog on a predator-free island in the Marlborough Sounds (Newman, 1996). The primary aim of a translocation involving this species is to reduce the likelihood of either stochastic or predator induced extinction by increasing the number of populations on predator-free islands. The following success criteria were determined prior to the translocation: repeated breeding events (evidence of juvenile production for more than 1 breeding season),