Habitat selection and cumulative impacts of habitat loss on Indo-Pacific humpback dolphins (Sousa chinensis) in Hong Kong

Abstract

Habitat selection allows wildlife to optimize prey acquisition and reduce predation risk that ultimately enhances their fitness. This behavior facilitates also essential responses to short-term disturbances and long-term habitat deterioration. Coastal species such as the Indo-Pacific humpback dolphin depend on shallow-water inshore habitats, which makes them susceptible to the changes in coastal environment, especially in areas such as Hong Kong where urbanization process is immense and rapid. In this study, the scale and rate of land reclamation and coastal infrastructure projects since 1970s were quantified using Landsat data and historic archives. Habitat selection function of Indo-Pacific humpback dolphins in Hong Kong was constructed to identify their habitat preference. Occurrence probabilities in the past (before major alterations) and future (when all currently planned projects are completed) were modelled to identify potential impacts from habitat alterations on dolphin distribution. We estimate that >4000 hectares of coastal humpback dolphin habitat were lost to land reclamation since 1970. The length of artificial shoreline has increased by 300%, reducing the proportion of natural shore from 90% to less than 65%. GLM analysis shows that humpback dolphins in Hong Kong prefer inshore areas < 30m deep, and there is a spatial heterogeneity in their preferences between shore types. They display strong affinity to natural shores in fine spatial scales and avoidance of artificial shores in larger scales. The modelled occurrence projections indicate that there has been a major drop of habitat usage near previous reclamation areas; and there will likely be a major decline in usage of current Marine Protected Areas due to intended and soon-upcoming habitat alterations. This study reveals that immediate and focused responses are needed to restrict habitat deterioration. It also demonstrates the vulnerability of humpback dolphins to future developments and the urgent need to revise current conservation management strategies in Hong Kong.