Researchers from City University of Hong Kong (CityU) asserts the success of trawl bans to improve biodiversity of marine organisms and recover marine benthos to drive oceanic revival.
By 2100, UNESCO predicts that more than half of planet’s marine species will be on the verge of extinction if efforts to protect biodiversity continue to fall short. In fact, 60% of marine ecosystems worldwide have been degraded or are currently facing severe exploitations. Such figures paint a bleak picture of the world’s collapsing ocean ecosystems and draw attention to the urgent need for collective action to mitigate the rapid destruction of oceanic environments.
Defying the somber status quo, researchers from City University of Hong Kong (CityU) have put forward promising findings of Hong Kong’s 2012 prohibition of trawling activities to revive the marine environment. Established 2.5 years ago, the ban focuses on trawling, which refers to a fishing method that uses nets to pull up fish from the bottom of the seabed or midwater. While seemingly harmless, trawling induces the suspension of ocean floor sediments that act as a source of food for many species living on the seabed. In effect, these creatures that call the seabed their home, better classified as benthic organisms, may die out due to lack of food or disruption of habitat.
The research team, spearheaded by Professor Kenneth Leung Mei-yee, CityU's Director of the State Key Laboratory of Marine Pollution (SKLMP) and Chair Professor in the Department of Chemistry, investigated the effects of the trawling ban on promoting oceanic recovery. Only the second study of its kind done in the tropics, they compared the physiochemical properties of sediment samples and diversity of benthic species from 28 water sites in Hong Kong before and after the trawl ban was put in place.
The importance of small benthic organisms cannot be overemphasised, since they play a vital role in the marine food chain as prey for larger creatures. Recovering these species may well be the key to restore the fisheries resource, as indicated by Professor Qiu Jianwen from Hong Kong Baptist University (HKBU).
The results of their study demonstrated the effectiveness of the prohibition to improve the profusion of species and benthic marine creatures, validated by the 76% rise in the average number of benthic species found in sediment samples after the introduction of the ban. This optimistic growth is coupled with a 25% reduction in suspended solids in the water column and 29% increase in organic matter in surface sediments, which suggest reduced disruption in benthic habitats.
In parallel, analogous research have noticed the improvement of fish and crustacean supply, as well as the growth in number and weight of all predatory fish in eastern and western waters of Hong Kong, following the trawl ban.
Evidently a silver lining for the environment, investigations on the effects of trawl bans are crucial to validate the efficacy of such policy changes, and turn the spotlight on rectifying trawl fishing and rehabilitating marine ecosystems.
Nevertheless, as befittingly pointed out by Prof Leung, "Apart from trawl ban, a multi-pronged approach can promote ecosystem restoration. For example, stop illegal trawling by increasing enforcement, improve water quality, impose a fish moratorium, control fishing gears, restrict the size of harvested fishes, establish fishery protection areas, and also minimise marine construction works.”