Trawl fisheries have been shown to cause overfishing and destruction of benthic habitats in the seabed. To mitigate these impacts, a trawling ban has been enforced in Hong Kong waters since December 31, 2012 to rehabilitate the ecosystem and enhance fisheries resources. Previous studies demonstrated that reduced trawling activities would increase the heterogeneity of benthic habitats, thereby enhancing species richness and abundance of benthic fauna and providing more prey resources for predatory fishes. This study aimed to test a hypothesis that the population and trophic dynamics of the Bartail flathead Platycephalus indicus, a heavily fished benthic predatory fish, at inner and outer Tolo Channel of Hong Kong (i.e., EI and EO) improved with increases in their body size, abundance, biomass, trophic niche, and trophic position after the trawl ban. Samples were collected from trawl surveys before and after the trawl ban to compare the pre-ban and post-ban populations of P. indicus from EI and EO. Body size, abundance, and biomass were assessed in 2004, 2013–2014, and 2015–2016, whereas trophic niche and trophic position were analyzed based on stable isotopes of fish samples collected in dry season of 2012, 2015, and 2018. Following the trawl ban, the abundance and biomass of P. indicus increased in EO, with body size increased in EI. Furthermore, as indicated by the results of stable isotope analysis (SIA) on their tissues and prey items, trophic niche, and trophic position of P. indicus increased in EI and EO, respectively. Our study demonstrated that the trawl ban had promoted the recovery of a predatory fish population through restoring size structure and trophic dynamics.
This research was substantially funded by the Research Grants Council of the Hong Kong SAR Government, Hong Kong, China via two grants from its Collaborative Research Fund scheme (CRF project numbers: HKU5/CRF/12G and C7050-18EF) to KL. VH, LT, and YM would like to thank the University of Hong Kong (HKU) for partially funding their research postgraduate study.
The authors would like to thank Helen Leung for her excellent technical support, and S. F. Leung, Director of Agriculture, Fisheries and Conservation Department for granting us a scientific research permit (R1710007 and R1710045) for conducting sampling using a shrimp trawler. The authors would also like to thank Archer Wong, Denis Chan, Kevin Ho, Kingsley Wong, Matthew Perkins, Racliffe Lai, Jason Yau, and Stella Wong for their assistance in the field survey and laboratory work. The authors would also further like to thank Thea Bradford for proofreading and improving the use of English on a draft of this manuscript.
- management intervention
- stable isotope analysis
- trophic level
- trophic niche