Conservation issues for Hochstetter's frog (Leiopelma hochstetteri): monitoring techniques and chytridiomycosis prevalence in the Auckland region, New Zealand : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Auckland, New Zealand
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Date
2009
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Massey University
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Abstract
Amphibians are suffering extinctions and range contractions globally. This is caused by
numerous factors and most of them are related to human activities. The overall aim of
this thesis was to make a significant contribution to the conservation of the endemic
amphibian Leiopelma hochstetteri through research. This was achieved by focusing in
two of the main conservation issues for this species, the need for standardised and
robust monitoring techniques to detect trends and changes in populations, and the
determination of the prevalence of chytridiomycosis, caused by the amphibian chytrid
fungus (Batrachochytrium dendrobatidis). Two populations of the Auckland Region
were selected for this study, one on the mainland (Waitakere Ranges) and the only
known offshore island population of this species (Great Barrier Island). For both study
sites different monitoring methods were used to obtain some population parameters.
Site occupancy models of MacKenzie et al. (2002) gave reliable site-specific
estimations of occupancy and detection probability using covariate information and
presence-absence data collected from 50 sites in the Waitakere Ranges and four
repeated visits during 2008. Elevation and distance searched were found to have an
important effect on occupancy levels, while time taken to search the site was important
variable determining detection probabilities. Also, parameters were estimated for three
age classes separately. Statistical models were used to infer abundance from occupancy
analysis, and results were compared with the distribution of relative abundances
obtained from repeated transect counts and an established sight/re-sight criterion. In
addition, the use of surrogate measures for relative abundance was explored. Detection
probability and the distance to first frog found were found to have a significant
correlation with relative abundance. These measures can be used to infer relative
abundance in future site occupancy surveys. Two surveys and a pilot site occupancy
survey were conducted on Great Barrier Island, and presence of frogs was confirmed atthe northern block, and in a small seepage in the central block. No new locations were
found. Waitakere Ranges and Great Barrier Is. populations were tested for the presence
of chytridiomycosis, and all frogs sampled tested negative (n = 124) which means that if
present chytridiomycosis prevalence is lower than 5% with a 95% confidence interval.
This and previous evidence suggests that L. hochstetteri may be resistant or immune to
the disease. However, to confirm this additional studies are needed.
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Keywords
Frogs, Endangered species, Environmental monitoring