Ecology of scree skinks (Oligosoma waimatense) in O tu wharekai wetland, mid-canterbury high country, New Zealand

Abstract

Many of New Zealand’s 104 lizard taxa are restricted to the country’s main islands where they are vulnerable to a range of threats. Information on population trends and basic ecological data are lacking for most species, hampering conservation efforts. We monitored a population of scree skinks (Oligosoma waimatense; conservation status: Nationally Vulnerable) in an alluvial stream bed in O Tu Wharekai Wetland in the mid-Canterbury high country over 10 years (2008−2018) to understand aspects of the population’s ecology, and to clarify potential threats and options for management. Although there was no linear trend in scree skink capture numbers over this time, an 84% decline was observed following severe and unseasonal flooding in May 2009. Capture numbers recovered over c. 8.5 years in the absence of any species management. Skinks ranged in size from 60−114 mm (snout-to-vent length). Home range size estimates varied from 39.5 to 950 m 2 (100% Minimum Convex Polygons) and their mean size was smaller than those reported for closely-related species. Photo-identification was not sufficiently accurate for long-term individual identification. Threats at our study site include severe flooding, predation by pest mammals, weed encroachment and human interference. Climate change is likely to increase future flood risk to this population and to other threatened species inhabiting the upland reaches of Southern Alps rivers. We recommend: (1) continued monitoring at our study site to assess long-term trends in a flood-prone population of scree skinks; (2) monitoring of four additional populations in scree habitat for 10 years to determine threats and management needs; (3) a survey of Black Jacks Island in Lake Benmore to determine whether the species (last seen there in the 1980s) is still present; and (4) the immediate removal of wilding conifers and other exotic trees from affected sites.