Improvements of Population Fitness and Trophic Status of a Benthic Predatory Fish Following a Trawling Ban

Abstract

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.

When the Trawl Ban Is a Good Option: Opportunities to Restore Fish Biomass and Size Structure in a Mediterranean Fisheries Restricted Area

“…The postban biomass increase in the GCAST had already been observed as early as 1994 [36], although supported by a much smaller dataset and a weaker statistical design than in the present work. Similar evidence of biomass increase was recorded in a few other trawl exclusion areas in the Mediterranean [52], the Atlantic Ocean [24,[81][82][83][84], and the Pacific Ocean [73], even though only a few studies [69,85] have considered the effect of protection on the whole trawlable assemblage rather than on a few target species.…”

“…Spatially explicit management has the potential to preserve ecosystem resilience and allow sustainable fishing and protection of habitats, community structure, and ecosystem functions [64,65]. Although fisheries-induced impacts may have evolutionary components that are hardly reversible, leading in some cases to the lack of recovery after protection [66], most of the partial or absent effectiveness observed in some cases has been explained mainly with unsuccessful habitat protection, lack of compliance, mismanagement issues, inappropriate planning, unexpected fish stock redistribution, modifications of fishing pressure, and impact from recreational fishing or fisheries-unrelated human activities [67][68][69][70][71][72][73].…”

Sharkless Makeup > Sharkless Oceans

“…Given the complexity and cost of deep-sea fishing methods (Cox, 2004. ), the recent increase in longline and bottom trawl fishing bans (Bloom Association, 2016; Bloom Association 2016b; Tao et al, 2021;Ward et al, 2007) and the surplus of sharks caught as bycatch through non-selective methods (Molina & Cooke, 2012), it seems unlikely that deep-sea sharks continue to supply the oil for squalane, or that solely deep-sea sharks like the basking shark are targeted. It is possible that the literature perpetuates a past truth by conflating squalane's richest known natural source with the species that comprise the actual current source(s).…”