Abundance and dispersal of translocated common skink (Oligosoma polychroma) on Ulva Island Helen Sharpe A report submitted in partial fulfilment of the Post-graduate Diploma in Wildlife Management University of Otago 2011 University of Otago Department of Zoology P.O. Box 56, Dunedin New Zealand WLM Report Number: 250 Abundance and dispersal of translocated common skink (Oligosoma polychroma) on Ulva Island A report prepared for the Department of Conservation in association with Otago University’s Diploma of Wildlife Management. Helen Sharpe July 2011 2 Abundance and dispersal of translocated common skink (Oligosoma polychroma) on Ulva Island Contents Summary 2 Introduction 3 Methods 4 Results 8 Discussion 9 Recommendations 13 Acknowledgements 15 References 16 Figures and tables 18 3 Abundance and dispersal of translocated common skink (Oligosoma polychroma) on Ulva Island Summary This report describes a monitoring study carried out in 2011 to investigate the abundance and distribution of common skink (Oligosoma polychroma) on Ulva Island, Southland, New Zealand. Common skinks were introduced to Ulva in 2005 and 2006 for ecosystem restoration, and to investigate effects of weka (Gallirallus australis scotti) predation. Skinks were monitored over 3 non-consecutive days using artificial cover objects. Where possible skinks were caught, weighed, measured and photographed. A total of 18 sightings were made which indicates a substantial drop in both populations but especially at West End Beach. A combination of insufficient habitat and predation/competition by weka are the probable causes. However some uncertainties with monitoring are acknowledged, with regard to sub-optimal weather conditions and ‘settling’ time for new ACOS. Skinks appear not to have dispersed more than 20-30 metres from their release site. Recommendations include further monitoring, supplementing the populations and trialling the use of smaller weka-proof exclosures in an area of good habitat. The projected drop in weka numbers due to ingestion of rat poison from a forthcoming eradication provides an opportunity for further research, population supplementation and introduction of green skink. Additional key words Gecko, national park, reptile, refuge Running head Monitoring translocated skinks on Ulva Island Introduction Translocation of fauna is an important conservation technique, both for species protection, and for ecosystem restoration (Armstrong and Seddon 2007, Germano and Bishop 2009). Reptile translocations are especially difficult (Dodd and Seigel 1991) but are being used 5 with increasing success (Sherley et al. 2010). One way to minimise the risks of translocation is to first work with more common relatives of the target taxa to identify and solve problems before introducing rarer species. An example of this technique is the reintroduction of common skink (Oligosoma polychroma) to Ulva island. Skinks were reintroduced there 5 and 6 years ago as part of ecosystem restoration and experimental work to evaluate effects 10 of weka predation. The process of reintroduction has 3 stages: survival of the release generation, breeding by the release generation, and persistence of the re-established population (Seddon 1999). On Ulva island, common skinks have survived and bred (Goodman et al. 2006) but trends in the population, as to both numbers and dispersal, are unknown. This project seeks to evaluate 15 the population size and location of skinks on Ulva island, and to make recommendations about further reintroductions of other reptiles such as geckos or the green skink (Oligosoma chloronoton). Background 20 Rakiura National Park (of which Ulva Island is part) has a nationally important lizard fauna, with 8 or more sympatric species within a small geographic range. It is also the southernmost diverse reptile community in the world (Department of Conservation 2011a). However, lizards here are vulnerable to exotic mammalian predators such as rats, cats and hedgehogs, as well as indigenous predators. An expansion in hedgehog range could 25 significantly endanger some species, which makes it important to ascertain the suitability of using islands like Ulva as a refuge. Reptile species proposed for introduction to Ulva island include green skink (threat status - Declining); jewelled gecko (Naultinus gemmeus - threat status - declining) and cloudy gecko 30 (Hoplodactylus nebulosus - threat status - relict) (Department of Conservation 2011b). Before introductions can occur, the suitability of island conditions for the species needs to be confirmed. In the case of green skink, this means that sufficient habitat is available and 5 that skinks can increase and maintain their numbers in the context of competition and predation from Stewart Island weka (Gallirallus australis scotti). 35 Common skinks were introduced to Ulva Island in 2005 from The Neck, a grassland peninsula about two kilometres southeast of the island. Initially 35 skinks were released into a 50m x 50m weka exclosure constructed near the research hut at Old Landing Bay. At that time, 10 corrugated-iron artificial cover objects (ACOs) were placed inside the 40 exclosure and four outside – for refuge and future monitoring. The population was monitored a year later, with 10 skinks found (Goodman et al. 2006). On the same day, 23 skinks (9 females, 10 males, 4 juveniles) were released under six ACOs at a different location, West End Beach. These ACOs were later supplemented by small pieces of onduline, to provide greater refuge opportunity from weka predation. 45 Methods Study site Ulva is a small forested island of around 266 ha located in Paterson Inlet, Stewart Island (figure 1). It was established as a scenic reserve in 1989 and is now part of Rakiura 50 National Park. The island is highly valued for its predator-free status, biodiversity and tourism values, and is managed as an ‘open sanctuary’ with free day-visitor access. Under the Rakiura National Park Management Plan (Department of Conservation 2011a), Ulva Island is considered a ‘special place’, requiring more specific management than the park as a whole. Management objectives include: increasing public awareness of ecosystem 55 restoration on the island and facilitating scientific study and research. Introduced mammalian predators were eradicated by 1997 and four threatened bird species reintroduced since 2000 – South Island Saddleback/Tieke (Philesturnus carunculatus), South Island Robin/Toutouwai (Petroica australis), Rifleman/Titipounamu (Acanthisitta chloris) and Yellowhead/Mohua (Mohoua ochrocephala). Unfortunately, Norway rats 60 (Rattus norvegicus) were found on the island in increasing numbers in late 2010 and an eradication programme is now underway (Department of Conservation 2011b). The predominant vegetation is podocarp forest, with a narrow strip of coastal scrub of leatherwood (Olearia colensoi), muttonbird bush (Brachyglottis rotundifolia) and inaka 6 (Dracophyllum longifolium (Michel et al. 2010). The island is heavily indented with sandy 65 or stony beaches, some of which are backed by a strip of more open vegetation such as grasses, club rush (Scirpus nodosus), Carex sedges and flax (Phormium tenax) (pers. obs). Study species New Zealand skinks are represented by a single genus, Oligosoma, which evolved through 70 rapid island radiation in the last 25 million years (Liggins et al. 2008, Chapple et al. 2009). The common skink is a small skink (snout-vent length to 80mm) found throughout the southern North Island, South Island and Stewart Island to an altitude of 1700m (Gill and Whittaker 1996, Lettink et al. 2011). Taxonomically it has undergone various revisions and is now considered a species complex, consisting of 5 geographically distinct clades 75 (Chapple et al. 2008). The study species belongs to Clade 5 which occurs in the south-east of the South Island from Canterbury to Stewart Island. Different colour morphs are recognised (Jewell 2008), the Stewart Island animals being light to mid-brown with attractive striping. The common skink is diurnal and a sun-basker, preferring dry, grassy, open areas with low 80 vegetation or logs and stones for cover (Wilson et al. 2007, Landcare Research 2011). It reproduces annually, bearing up to 10 live young in December-February. Diet consists of a wide range of arthropods, supplemented with berries. Conservation status is ‘not threatened’ (Hitchmough et al. 2010), however local extinctions appear to be occurring (Frank and Wilson 2011). 85 Objective, design and preliminary work The primary objective was to assess skink numbers and distribution using multi-day counts from artificial cover objects (ACOs). The original ACOs had been informally monitored from time to time, with skinks seen under them (Goodman et al. 2006, Brent Beaven pers. comm.). These ACOs were supplemented with new ones (corrugated iron or Onduline), to 90 maximise the number of sightings and assess distribution away from the original release points. Secondary objectives were to obtain morphometric and photographic data from caught skinks, and to assess habitat with a view to further reptile reintroductions. Preliminary work was carried out to identify ACOs, check their suitability, and plan locations for new covers. Any skinks seen were recorded but not as part of the official 7 95 monitoring. On January 18 2011 the original ACOs were searched for and lifted. Many covers in the weka exclosure appeared untouched since the original release, and were overgrown and compacted, consisting of 3-5 layers of iron in