Absence of Ship Rat Rattus rattus, and Norway Rat Rattus norvegicus, on Ouvea (Loyalty Islands, New Caledonia): consequences for conservation

Abstract

A rat trapping campaign was conducted from July to December 1994 on Ouvea in the Loyalty Islands, New Caledonia. Locations of rat traps took into account different geographic sectors (North, Centre, South and Islets) and different habitats (forest, crop fields, coconut plantations, houses). The campaign encompassed a total of 1 363 trap nights and autopsy data were collected on rodents that were captured. Vertebrate remains from Barn Owl roosts were also collected and examined to determine which rat species were present. For the whole campaign the corrected trap success rate was 9.5 rodents per 100 trap nights. No significant variations in the trap success rate were observed in relation to geographic sector or habitat. Ninety-eight rodents were captured and 64 identified: six Mus musculus and 58 Rattus exulans. No Rattus rattus and no R. norvegicus were caught. Similarly, the only species identified from material found in Barn Owl roosts were M. musculus and R. exulans. Observation of the fauna and environment on Ouvea provided some indirect evidence to confirm the absence of both R. rattusand R. norvegicus. The history and geographical characteristics of Ouvea, and certainly chance, could explain the fact that these two species never reached the island. With regard to rat species, Ouvea's situation is remarkable and unique in the Pacific for inhabited islands of comparable size and level of development. Considering the dramatic and well known effects resulting from the introduction of rat species such as R. rattus and R. norvegicus on small Pacific Island environments, the authors have alerted local authorities and the population of Ouvea, and have proposed initial measures as part of an action plan.