Tools for managing threatened species: improving the effectiveness of whio conservation
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Conservation frequently requires immediate responses to prevent further declines of imperilled populations, often in the absence of detailed information. Consequently, population distribution patterns are often used to guide conservation decisions. However, distribution patterns may be misleading if threats have restricted species to low quality habitat. This issue means it is not always apparent where management efforts should be concentrated for maximum conservation gain. My aim was to improve the effectiveness of threatened species conservation by investigating this issue in whio (blue duck - Hymenolaimus malacorhynchos), a New Zealand riverine duck that has undergone serious declines. I used population and spatial modelling to answer three questions: (1) what are the threats to whio, (2) how can these threats be managed, and (3) managing which whio habitats will give the greatest conservation gain? A spatial analysis of contemporary whio habitat using boosted regression trees revealed whio are only secure in 1 % of their historical range, with predation likely causing significantly greater range contraction (83 %) than habitat modification (29 %). In that analysis, I identified 39,000 km of occupiable whio habitat, providing extensive opportunities to expand their contemporary range through management. Intensive monitoring identified stoats (Mustela erminea) as the primary cause of whio population declines, with stoat predation severely reducing whio nest survival (10 % and 54 % in the absence and presence of stoat control, respectively). Population viability analyses indicated whio populations in the absence of stoat control were at high risk of extinction (λ = 0.74) but large-scale, low-intensity predator control was useful for short-term whio conservation. However, whio populations with stoat control still had a declining population growth rate (λ = 0.95) and further intervention may be required to prevent whio extinctions. Such management needs to target high quality habitat to ensure the greatest conservation value. Analyses of habitat quality revealed whio fitness was highest in warm, low gradient rivers, although fitness gradients differed between North and South Islands. Comparisons of fitness relationships with spatial model predictions showed that South Island whio occurred more frequently in poorer habitat, indicating they may occupy a relict distribution. Limited resources for conservation mean identifying effective management techniques is critical for species persistence. My modelling approach enabled the effectiveness of whio management to be assessed and areas of high quality habitat where such management should provide the greatest benefit to be identified. These tools are directly applicable to the conservation management of many threatened species by quickly informing managers in situations where distributions may not follow habitat quality.