Conservation of Brothers Island Tuatara (Sphenodon Guntheri)

Abstract

Brothers Island tuatara (Sphenodon guntheri) is one of the rarest reptiles in the world. Between 1995 and 1998, I studied fundamental aspects of its life history and demography, monitored and assessed results of the first contemporary tuatara translocation, and analysed the long term viability of existing and proposed populations. North Brother Island supports the only self-sustaining population of Brothers Island tuatara. About 350 adults are restricted to this single island of 4ha in Cook Strait, New Zealand. High annual adult survival (0.93 for males and females) and longevity (61-71 years) have been estimated from analysis of ten years of capture-recapture data and a point sample 40 years ago. Viability analysis, using the computer program VORTEX, indicates this population has a high probability of long-term survival, but that sex ratio, harvesting and small population size are primary risk factors. Genetic and environmental stochasticity were unable to be included in these analyses due to lack of information on effects. In 1995, 68 tuatara were translocated from North Brother to Titi Island, Marlborough Sounds, New Zealand. During 26 months of monitoring, 51% of released tuatara were recaptured. Adult tuatara on Titi Island are in better condition, as indicated by weight/length comparisons, than adults on North Brother Island. Translocated juveniles have increased by up to 106% in weight. Evidence exists for breeding on Titi Island. The translocation is progressing successfully, but it will take decades to confirm establishment. This population has a high probability of survival, but would benefit in the short-term from supplementation in the next ten years. The New Zealand Department of Conservation proposes to establish a third wild population of Brothers Island tuatara on Matiu/Somes Island. Population viability analysis was carried out to test founder scenarios for this population. A population founded on 20 adults (10 females and 10 males) harvested from North Brother Island and 29 juveniles available from a head-start program, had a high probability of long term survival. In summary, the conservation status of Brothers Island tuatara is improving and programmes appear to be progressing successfully.