Translocation site selection for the nationally endangered grasshopper species Brachaspis robustus : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science at Lincoln University

Abstract

The robust grasshopper (Brachaspis robustus) is one of the most endangered invertebrates in New Zealand. This species is at risk of extinction due to the compounding pressures of mammalian predation, habitat modification, and climate change. Protection of this species and its habitat is vital to its survival. One tool that has been identified to help manage B. robustus is translocation to suitable environments. In my research, I aimed to understand factors critical to developing an effective conservation translocation plan for B. robustus. Five potential translocation sites were selected closer to the Southern Alps than existing B. robustus populations, as it is thought this may be necessary to protect against future temperature increases that could affect successful egg diapause, a necessary part of the grasshoppers’ development. These sites were evaluated for key threats to the species and how to mitigate them, as well as habitat suitability. A capture-mark-recapture study was done to determine the area individual grasshoppers occupy to inform us on how much space is required at a translocation site to support a B. robustus population. Results showed that over 17 days B. robustus were usually found within 16 m of the original capture location, however, one individual was found almost 50 m away from the original capture spot after one day. Microhabitat preference as investigated by assessing ground cover within 1 m of individual grasshoppers at two locations (Snowy River and Ōhau River) and comparing that to ground cover in the wider environment. Ground cover surveys were then replicated at the potential translocation sites. Brachaspis robustus were most commonly found on small rocks (1 – 10 cm diameter) with very minimal vegetation cover. Only 3/143 (2.1%) grasshoppers were found within 1 m of vegetation over 2 cm tall with no difference between male and females. In contrast, 46% of quadrats surveyed in the wider habitat contained vegetation with a mean top height of >2 cm, including 31.1% >20 cm. Presence of native and introduced predators and level of predator control at currently occupied sites compared to potential translocation sites was investigated. Native and introduced predators were found to be present at all sites, but mammalian predator control is currently being undertaken at Cass and Tasman Rivers. The risk of hybridisation was evaluated by assessing maps for suitable B. nivalis habitat. Searches were undertaken to determine B. nivalis presence and access to potential B. robustus translocation sites. The risk of hybridisation is high on the Tasman River due to proximity of B. nivalis. The collated results showed that the most suitable translocation site for this species is the Tasman River. This site is most similar in rock size composition to Snowy River and is large enough for translocation. It has the lowest cover of tall vegetation and is the most protected against mammalian predators. This site is closest to the Southern Alps, mitigating against future global warming. However, the risk of hybridisation may be increased there as B. nivalis occupy nearby habitats. Further work must be done to understand this risk.