Occupancy and relative abundances of introduced ungulates on new zealand’s public conservation land 2012–2018

Abstract

Introduced ungulates are an important management issue on New Zealand’s public conservation land (PCL). Ungulates are harvested by recreational and commercial hunters, with some government-funded culling. A robust monitoring system is needed to reliably report trends in occupancy and abundance, and to evaluate management effectiveness. We first describe the design and implementation of a monitoring programme enabling ungulate occupancy and relative abundances to be estimated on New Zealand’s PCL. Monitoring sites are located at the vertices of an 8-km grid superimposed over PCL on North, South and Stewart/Rakiura islands (i.e. a spatially representative sampling network). At each site, intact ungulate pellets are counted on four transects radiating from a 400 m2 vegetation plot, with each 150 m transect containing 30 1-m radius plots. We next report an analysis of the first such data collected at 1346 sites during 2012–2018. Nationally, ungulate occupancy and abundance were higher at woody than at non-woody sites, and overall were higher in the North Island than in the South Island. Occupancy odds increased by 34% and 21% per annum in the North Island and South Island, respectively. Abundance (conditional on sites being occupied) increased 11% annually in the North Island, but did not change in the South Island. These increases in occupancy and abundance indicate that ungulate populations are recovering from the lows of the 1980s, likely due to reduction in both commercial harvesting and government-funded control. The data from the monitoring reported here establish a baseline against which future estimates of ungulate occupancy-abundance, and the effectiveness of management activities, can be assessed. Five-yearly remeasurements at the sites, coupled with more comprehensive recording of information on government control and commercial/recreational harvesting activities, should enable the drivers of future changes in ungulate occupancy and abundance to be better understood.