Trawling has been demonstrated to be one of the most destructive fishing methods to marine benthic communities. Since the 1970s, marine fishery resources in Hong Kong, especially large predatory species, have been overexploited by non-selective fishing gears including bottom and pelagic trawlers. ‘Fishing down the food web’ has resulted in a benthic ecosystem primarily dominated by small, lower-trophic level (herbivorous and omnivorous) fishes and crustaceans. To mitigate such impacts, the Government of the Hong Kong Special Administrative Region has implemented a territory-wide trawling ban in local waters since 31 December 2012. Using stable isotope analysis, this study investigated whether benthic crustacean communities, in particular Decapoda (crabs and prawns) and Stomatopoda (mantis shrimps) across six zones of coastal waters of Hong Kong, have undergone recovery following the trawl-ban. We hypothesized that both trophic niches width and levels would increase in consumers after trawl-ban.
Results/Conclusions
Our results showed that there was a greater trophic niche diversity in four studied crustacean communities three years after the trawl-ban, when compared to those of 2012 (before the trawling ban). Using Bayesian standard ellipse areas, we further compared the niche width of target crustacean species representing known functional groups (carnivore and omnivore) before and after the trawl-ban. Only two carnivorous species, namely Charybdis feriata and Oratosquilla oratoria, changed their niche width after the trawling ban, showing an expansion in dietary composition of Charybdis feriata. Such changes were likely linked to ecosystem recovery within the southeast waters, waters around Lamma and outer estuary, while the dietary composition of Oratosquilla oratoria only expanded within inner estuary after the trawl-ban. Further analyses are currently being conducted to assess whether the mean trophic level of carnivorous crustacean communities increases after the trawl-ban. The variation of isotopic signatures in the consumers before and after the trawling ban will be discussed in light of their life history traits (e.g. size), food sources, and substratum heterogeneity.