TRAP CATCH AS A RELATIVE INDEX OF FERRET (MUSTELA-FURO) ABUNDANCE IN A NEW-ZEALAND PASTORAL HABITAT

The density of a ferret population in South Island pastoral farmland w as estimated by live capture, mark and release, and by removal trappin g, during March and April 1997. An estimate of 6.3 ferrets per km(2) ( 5.5-8.4, 95% CI) was obtained after 8 days of mark and release, wherea s 10 days of removal trapping provided an estimate of 5.3 ferrets per km(2) (5.3-5.9, 95% CI). There was significant variation in individual trappability. Proportionally more unmarked ferrets were captured as p opulation density was reduced during removal trapping. Four person-day s effort were required to remove 50% of the ferret population from an area of 1254 ha, while removal of 80 or 95% of the population took con siderably greater effort. Trapping provided a reliable relative index of ferret abundance. While there is a need to replicate this study in order to confirm its validity, it confirms the use of a relative index as a valuable tool for measuring the efficacy of control operations a nd estimating ferret abundance.