4.7 Article

Stable isotope analyses reveal anthropogenically driven spatial and trophic changes to Indo-Pacific humpback dolphins in the Pearl River Estuary, China

Journal

SCIENCE OF THE TOTAL ENVIRONMENT
Volume 651, Issue -, Pages 1029-1037

Publisher

ELSEVIER
DOI: 10.1016/j.scitotenv.2018.09.256

Keywords

Carbon; Nitrogen; Sousa chinensis

Funding

  1. Natural Science Foundation of China [41576128]
  2. Provincial Natural Science Foundation of Guangdong in China [2017A030308005]
  3. Ocean Park Conservation Foundation of Hong Kong
  4. Sousa chinensis Conservation Action Project, China

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As long-lived apex predators in the Pearl River Estuary (PRE) of China, Indo-Pacific humpback dolphins (Sousa chinensis) are particularly vulnerable to anthropogenic impact and may undergo considerable ecological trait changes. The variability of traits, however, is often difficult to trace back in nature. Here, we analyzed stable isotope ratios of carbon and nitrogen inmuscle samples of 88 S. chinensis stranded in the PRE from 2004 to 2016 to investigate the ecological changes occurring in the dolphins. Stable isotope analysis revealed the existence of two sub-aggregations of S. chinensis in the PRE. Generalized additive models showed significant decreasing trends in both carbon and nitrogen isotopic signatures over time, indicating the habitat changes and dietary shifts, possibly due to the influence of increased coastal developments and fishing activities in the PRE. Diet modeling suggests that the proportional contribution of higher trophic-level prey decreased in the S. chinensis diet over time, while increased consumption of lower trophic-level prey was observed. This shift was related to depletion of higher trophic-level prey caused by overfishing. Although S. chinensis could temporarily compensate for the lost energy supply through feeding plasticity (revealed by the negligible differences of isotope niche width among different stranding periods), long-term depletion in prey availability may cause long-lasting negative effects on this dolphin population. This study highlights the crucial relationships between fishery management and dolphin conservation, providing scientific evidence for the long-termprotection of this threatened species in the PRE region. (c) 2018 Elsevier B.V. All rights reserved.

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