A Trawl Disturbance Indicator to quantify large scale fishing impact on benthic ecosystems

▸ Proposal of an indicator of the benthic community health to assess trawling disturbance. ▸ This indicator is based on the composition of biological traits of epifauna. ▸ Epifauna was surveyed at 6 soft-bottom sites over the Spanish Mediterranean coast. ▸ The biological traits significantly reflected the ecosystem disturbance. ▸ A Trawl Disturbance Index (TDI) was proposed as a tool for fisheries managers. We evaluated the adequacy of an indicator of benthic community health to assess trawling disturbance by sampling epifauna at 6 sites subjected to variable fishing intensity in the Mediterranean: from no fishing, in an area associated to a marine reserve, to high fishing intensity, in trawling grounds. The proposed indicator is based on the biological traits composition of epifaunal species that determine vulnerability to trawling: mobility, fragility, position on substrata, average size and feeding mode. Five groups defined by the combination of these biological traits represented different levels of vulnerability to trawling. Results based on analysis of the relative abundance of these groups at each site showed that the biological traits significantly reflected ecosystem disturbance, with the less disturbed communities having the highest abundance of groups considered vulnerable to trawling. According to these findings a Trawl Disturbance Index (TDI) was proposed as a tool for fisheries managers to assess the ecosystem health.