Using Passive Acoustic Monitoring to study behaviour and habitat use of Indo-Pacific Finless Porpoise (Neophocaena phocaenoides) in Hong Kong S.A.R. Waters
Le Double, S. L., Porter, L., Scheidat, M
Indo-Pacific finless porpoise reside in coastal areas of Asia. Their habitat overlaps with areas in which there is intense human use, such as the Hong Kong S.A.R. waters. Here the aquatic environment is severely compromised and porpoise face a range of threats, such as pollution, resource loss through over-fishing, bycatch in fisheries, underwater noise and habitat destruction. Over the last decades an increase in annual strandings and a decrease in local abundance have led to growing concerns over the conservation status of the local Hong Kong population. Finless porpoise behaviour and habitat use is still poorly understood, but is needed to design effective conservation measures. This species can be challenging to study at sea due to the small size, lack of a dorsal fin and inconspicuous behaviour. Finless porpoise do, however, produce narrow band high frequency echolocation clicks to navigate, communicate and forage. This feature has led to the proposal by the IWC in 2005 that acoustic monitoring be explored as a potential monitoring tool. The main aim of this study was to investigate patterns in habitat use of finless porpoise around the coast of Lamma Island, an area where many stranded porpoise have been collected. Acoustic data was collected using autonomous acoustic loggers (CPODs) and environmental data was obtained from government monitoring programmes. Generalised additive models (GAM) showed clear diurnal patterns with most click activity recorded at night. There was some evidence for seasonality of occurrence linked to Hong Kong wet and dry seasons. Part of the data could be analysed for the occurrence of foraging behaviour from click patterns. In future studies, this type of analyses could help provide a better understanding of how prey availability influences porpoise habitat use. Passive acoustic monitoring is an effective tool to continuously obtain data on habitat use and behaviour of finless porpoise. PAM data, in particular if collected over a larger area, would provide valuable input for management measures to conserve the population of Hong Kong finless porpoise.