Mortality mitigation of a translocated rare New Zealand frog Leiopelma pakeka
Authors:   , Karst Tanya M. 
Published: November 2021

<p>A small population (n=58) of Maud Island frogs, Leiopelma pakeka, was translocated to the Zealandia wildlife sanctuary in Wellington, New Zealand in 2006/2007. The 29 frogs that were released into a predator-proof enclosure, along with some of their progeny, are currently spread over three separate predator-proof enclosures. However, their status has not been assessed since 2011. With the aim of establishing a viable, freeranging population, the remaining 29 frogs were released into forested habitat around the original enclosure. In 2010, the translocation of the free-ranging population was assessed as a failure, citing too few founding individuals, inadequate habitat, predation by little spotted kiwi (LSK), Apteryx owenii, and predation by house mice, Mus musculus, as potential factors. This thesis re-addresses the status of L. pakeka in the three enclosures, as well as the potential predation of these threatened endemic frogs by LSK and mice. Survival of L. pakeka in the three enclosures was estimated by nocturnal emergence over 11 ve-night capture periods from October 2012 - August 2013. Identi cation of individuals was via photography utilizing distinguishable skin patterns and iris vessel (eye venation) patterns. The relocation of six adults after a 2011 census, including one inadvertently missed frog found during this study, left 19 adult frogs in the original enclosure, which continued to survive well, with 18 adults recaptured. In addition, juveniles of varying ages were seen throughout this study. In total, 34 recently metamorphosed froglets were released into a second enclosure over the years of 2008, 2009 and 2011. Night monitoring indicated only 8 individuals had survived, but a full enclosure census on 8 May 2013 revealed 12 of the 34 individuals (35%) had survived. Three of these frogs were then relocated to the Te Mahanga, publicly viewed enclosure. Emergence during the 11-month period indicated that the six frogs relocated to this enclosure from the original enclosure in October 2011 had survived; however, only two out of the three frogs that were relocated there after the May census had emerged. Additionally, two juveniles of unknown age were also seen in this enclosure. Potential predation by LSK was assessed by a ve-night video analysis (23-28 June 2013) of foraging behavior in the presence of mesh-protected L. pakeka. Out of the 668 videos reviewed, only three videos provided foraging behavior that helped ascertain whether LSK exhibited a potential interest in L. pakeka as a prey item. These videos showed that LSK failed to indicate a strong response to the presence of the frog, suggesting that the LSK in Zealandia do not have a strong predatory interest in L. pakeka. To investigate the potential causes of the free-range translocation failure, the habitat was enhanced with more rocks, a kiwi-exclusion fence was erected, and a further 101 L. pakeka were translocated from Maud Island to Zealandia on 2 December 2012. The frogs' survival as well as mouse activity levels (indicated by the presence of mouse prints in tracking tunnels) were monitored over nine ve-night capture periods from 17 December 2012 - 2 August 2013. Eighty-six out of the 101 translocated frogs were recaptured. Identi cation of individuals was via photography utilizing distinguishable skin patterns and iris vessel (eye venation) patterns, or by unique toe-clip combinations. Despite previous assessments, four surviving adults from the 2006/2007 translocation were recaptured as well as 12 of their progeny, resulting in a total of 117 Maud Island frogs for this study. Jolly-Seber analysis indicated high overall survival (0.914, 0.87/0.94, 95%CI), but temporally the population estimates indicated a negative regression starting at the second capture period (slope= -4.69, -6.70/- 2.68, 95%CI). With overall frog emergence, a negative binomial generalized linear model did not show signi cance in mouse activity levels, precipitation during sampling nor precipitation in the previous 24 hours (p>0.05). However, temperature did show a positive correlation to overall frog emergence (p<0.001) while relative humidity approached signi cance (p=0.0517) and indicated a potential positive trend. This study could not conclusively indicate whether A. owenii or M. musculus prey upon L. pakeka. However, it does suggest that the protected predator-proof enclosures may provide appropriate conditions for the ongoing survival and successful breeding of the endemic anuran. The study also suggests that LSK do not have a strong predatory response to the presence of Maud Island frogs, nor did increased levels of mouse activity have a signi cant e ect on the emergence of the 117 Maud Island frogs. Additionally, the discovery of the four survivors and 12 of their o spring indicates that the original translocation did not entirely fail. This newly acquired knowledge suggests that with the current mammal eradication program, Zealandia may continue with the establishment of a viable, free-ranging population of L. pakeka. Continued monitoring of all Maud Island frogs in the Zealandia sanctuary is recommended as a conservation measure, especially as mice have now established on its original island habitat.</p>