Mitigation translocation for conservation of New Zealand skinks

Abstract

<p>Worldwide, human development is leading to the expansion and intensification of land use, with increasing encroachment on natural habitats. A rising awareness of the deleterious effects of habitat destruction on species and ecosystems has increased the use of strategies intended to mitigate these negative impacts. One increasingly common strategy is mitigation translocation, the movement of living organisms from a future development site to another location in an effort to mitigate damage caused. Mitigation translocations may be implemented due to legislation or regulations in many jurisdictions, and in many instances command more resources than purely conservation-motivated translocations. Although they are intended to reduce or offset harm, the effectiveness of mitigation translocations as a conservation strategy has been questioned. I investigated the effectiveness of mitigation translocations for achieving conservation outcomes, using the study system of endemic New Zealand skinks. New Zealand’s skinks show a high level of endemism, are threatened by habitat loss and predation by introduced mammals, and are increasingly subject to mitigation translocations, making them an ideal study system for investigating mitigation outcomes. I investigated: whether mitigation translocations are meeting conservation goals; how the implementation and legal requirements of mitigation translocation relate to conservation goals; and how mitigation translocation practices might be improved to achieve better conservation outcomes. A technique used in mitigation translocations of lizards in New Zealand is the construction of rock piles as habitat enhancement at the receiving site. I developed a novel use of computer game physics software to model the three-dimensional interstitial spaces within such rock piles, and used this model to design rock piles with the aim of protecting translocated skinks from mice (Mus musculus), New Zealand’s smallest introduced mammalian predator. The protection is achieved by selecting rocks to optimise the size of interstitial spaces to be accessible to skinks but not to the larger mice (or other larger predators). This rock pile design could be used to improve survival of skinks both in translocations and other situations such as backyard conservation or restoration. The modelling technique I developed could be used for investigation of refuge space more widely, for instance in other terrestrial systems or aquatic systems. I also took part in a mitigation translocation of lizards at Transmission Gully near Wellington, New Zealand. I used this translocation to test my rock pile design, and as a case study of the challenges facing mitigation translocations and the barriers to conservation success. In addition, I revisited nine historical mitigation translocations of skinks (7–14 years post translocation), took surveys of current populations to assess their success at meeting conservation goals, and found a success rate of 22%, considerably lower than conservation translocations of New Zealand skinks (success rate of 88.9%). Despite this, all but one met their goals of fulfilling legislative requirements. Mitigation translocations fail to result in conservation benefit due to their implementation and goals. The goals of mitigation translocations are rooted in legislation, and vary due to inconsistent application of relevant laws (in New Zealand, the Wildlife Act 1953 and the Resource Management Act 1991), and the fact that the requirements under these laws do not necessarily reflect conservation goals. Additionally, mitigation translocations may be undertaken even when evidence indicates that meaningful conservation outcomes are unlikely (as in the case of the translocation at Transmission Gully). Failure may also be due to poor implementation; examples from case studies here include failure to control predators, low standards of planting at receptor sites, and small founder populations. To improve conservation outcomes, legal requirements for mitigation translocations should be implemented to require biologically-relevant goals (including a no net loss of biodiversity standard) and management techniques, and alternative methods of meeting conservation goals should be considered where appropriate.</p>

Use of constructed rock piles by lizards in a grassland habitat in Otago, New Zealand

“…This was because the estimated abundance of McCann's skinks had significantly increased in magnitude by ≥ 10% in the period between 4 months and 2.4 years following construction and there was no evidence of a temporal decline in abundance of any lizard species present on the constructed rock piles. This outcome reflects the finding by Lennon (2019) that while mitigation translocations of lizards in Aotearoa usually fulfil legal requirements, they do not necessarily result in meaningful conservation outcomes. We strongly recommend that consents granted for future habitat enhancement attempts require a monitoring programme that can determine effects on lizard populations instead of only documenting habitat use.…”

“…While reptile species readily use enhanced habitats, fewer studies demonstrate any benefits for reptile populations (Herbert 2020). Furthermore, few studies have documented the responses of Aotearoa reptiles to habitat enhancement (Hoare et al 2007;Lettink et al 2010;Knox et al 2012;Lennon 2019;Herbert 2020). Therefore, further case studies of reptile responses to habitat enhancement attempts are sorely needed to inform conservation and ecological consulting practice both in Aotearoa and internationally.…”

“…Additionally, under the Resource Management Act 1991, organisations undertaking specific resource management activities that may adversely impact the habitats of indigenous species must avoid, remedy, or mitigate these effects. However, the outcomes of ecological effects mitigation efforts for Aotearoa-endemic lizards often go undocumented, are inconclusive, or are only monitored for a short period of time (Lennon 2019).…”

“…As part of the lizard mitigation package, OceanaGold was required to build new rock piles to provide lizard habitat in the area adjacent to the Coronation Project site. Construction of refugia using artificial rocks or rubble has successfully provided habitat for reptile species in Australia and England, but were untested in Aotearoa before 2019 (Showler et al 2005;Croak et al 2010Croak et al , 2013Lennon 2019;Herbert 2020). Because of this lack of knowledge, the rock piles and their immediate edges were monitored for 2.4 years post-construction to determine: (1) which lizard species used the newly created habitats and (2) the temporal trend of each species' abundance within these habitats.…”

A review of New Zealand native frog translocations: lessons learned and future priorities

“…If a site is at or near carrying capacity, there is a risk that introducing additional individuals will result in mortality or dispersal of either the released frogs, or some of the resident population, thus providing no net gain to the population or species (Germano et al 2015;Sullivan et al 2015). Evidence from mitigation translocations for New Zealand lizards indicates that success rates are lower, IUCN best practice is not often followed, and the long-term monitoring necessary to assess success is rarely carried out in line with these global trends for mitigations regardless of taxa (Germano & Bishop 2009;Germano et al 2015;Sullivan et al 2015;Romijn & Hartley 2016;Lennon 2019;Bradley et al 2020).…”