Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

The effect of handling under anaesthetic on the recapture rate of wild ship rats (Rattus rattus).

Abstract

This paper describes a two-part study of small predators in New Zealand forests. First, during 12 days of live-trapping, 31 wild ship rats were captured, tagged and released: 9 were handled while anaesthetised using halothane and 22 were handled while conscious using gloves. There was a significant difference between the two groups of ship rats in live-recapture rate: 4 out of 9 rats that had been handled while anaesthetised were recaptured alive, compared with 0 of 22 that were handled while conscious. Second, during 12 days of removal-trapping, 23 ship rats were killed, of which 6 were tagged, including 4 of the 9 that had been previously handled while anaesthetised (2 of which had also been recaptured alive during the live-trapping) and 2 that had previously been handled while conscious. These observations have implications for the statistical estimation of population density from capture-mark-recapture data and for the development of protocols for minimising stress in captured animals, especially nocturnal species released from traps in daylight.