The deposition in growth layer groups (GLGs) in dolphin teeth provides a temporal archive of the nitrogenous input, which can be valuable in studies of their foraging ecology and environmental conditions.  In terms of foraging ecology, the weaning age (a stage of transition from milk to solid prey consumption) can be reflected by trophic level shift across life stages.  The weaning age of Indo-Pacific humpback dolphins (Sousa chinensis), locally in Hong Kong and China known as Chinese white dolphins, remains poorly known, although a recent photo-ID study off Taiwan indicates that mother-calf social separation occurs after 3-4 years.  On the other hand, as delphinids occupy higher trophic levels, tracing back any shift in δ15N may provide indications of anthropogenic impacts.  We hypothesize that N-enriched sewage source that enters coastal environments is sufficiently variable so that δ15N in dolphin teeth may indicate the N provenance. In my postgraduate study, I apply stable isotope analysis to investigate (i) the ontogenetic shifts in the diet of Chinese white dolphins, (ii) determine their weaning age and (iii) document the trend in N-pollution in the Pearl River Estuary (PRE).  This study will provide insights into individual dietary life history that cannot be obtained through traditional field observations of free-ranging dolphins, and, with further analyses of dolphin teeth from several locations across the PRE, it will use these long-lived marine mammals as bio-indicators of the region’s environmental history.

Another part of my postgraduate research involves acoustic environment of humpback dolphins in Hong Kong waters. I focus primarily on soundscape, the collection of environmental sound, biological sound, and anthropogenic noise, which represents the important sensory signal for the habitat selection of any cetacean. Long-term noise can alter the soundscape, and disrupt the acoustic communication of soniferous organisms. The Pearl River Estuary is among the world's most developed coastal regions, with massive coastal developments and construction projects that span across the entire estuary, which generate intense underwater noise. The resulting impacts on marine mammals inhabiting this shallow-water coastal habitat are likely vast and unceasing, yet very little of it has been adequately investigated. In this project, as part of my Lab’s ongoing long-term field research surveys, I map the soundscape of Hong Kong waters and, with the use of long-term recording stations, I collect large volume of underwater recordings. Through this intensive year-round research effort, I will investigate the habitat use and acoustic behaviour of various marine animals inhabiting Hong Kong waters, including soniferous fishes and invertebrates, and of course the two coastal cetacean species that are found in Hong Kong year round, the Indo-Pacific humpback dolphin and Indo-Pacific finless porpoise (Neophocaena phocaenoides). This part of my postgraduate research will apply also machine learning techniques to separate biological and non-biological sound from noisy field recordings, which can provide more information on prey availability, biodiversity, habitat quality, and human activities.

This somewhat unconventional combination of biochemical techniques with bioacoustics represents an exciting new avenue of multifaceted and cross-disciplinary approach to studies of marine mammals, and complements very well my Lab’s ongoing, long-term research in behavioural-, population- and conservation ecology.

Biochemical and Bioacoustic study of Indo-Pacific Humpback Dolphins: Ontogenetic shifts, soundscape, and environmental history of the Pearl River Delta