1. Bottom-trawl fisheries are the most-widespread source of anthropogenic physical disturbance to seabed habitats. Development of fisheries-, conservation- and ecosystem-based management strategies requires the selection of indicators of the impact of bottom trawling on the state of benthic biota. Many indicators have been proposed, but no rigorous test of a range of candidate indicators against 9 commonly-agreed criteria (concreteness, theoretical basis, public awareness, cost, measurement, historical data, sensitivity, responsiveness, specificity) has been performed. 2. Here, we collated data from 41 studies that compared the benthic biota in trawled areas with those in control locations (that were either not trawled or trawled infrequently), examining 7 potential indicators (numbers and biomass for individual taxa and whole communities, evenness, Shannon-Wiener diversity and species richness) to assess their performance against the set of 9 criteria. 3. The effects of trawling were stronger on whole-community numbers and biomass than for individual taxa. Species richness was also negatively affected by trawling but other measures of diversity were not. Community numbers and biomass met all criteria, taxa numbers and biomass and species richness satisfied a majority of criteria, but evenness and Shannon-Wiener diversity did not respond to trawling and only met few criteria, and hence are not suitable state indicators of the effect of bottom trawling. 4. Synthesis and application. An evaluation of each candidate indicator against a commonly agreed suite of desirable properties coupled with the outputs of our meta-analysis showed that whole-community numbers of individuals and biomass are the most suitable indicators of trawling impacts as they performed well on all criteria. Particular strengths of these indicators are that they respond strongly to trawling, relate directly to ecosystem functioning, and are straightforward to measure. Evenness and Shannon-Wiener diversity are not responsive to trawling and unsuitable for the monitoring and assessment of bottom trawl impacts.05-Mar-2020

Data were collated from published comparative studies of the effects of bottom trawling on seabed habitat and biota following a systematic review protocol, thereby including all available studies and avoiding selection bias (Hughes et al., 2014). The methods were designed to identify and collate evidence from comparative control-impact studies to identify changes in state of benthic biota resulting from mobile bottom fishing. The searching strategy is documented in Hughes et al. (2014), which specifies the databases searched and search terms used in detail. Data were collated from published comparative studies of the effects of bottom trawling on seabed habitat and biota following a systematic review protocol, thereby including all available studies and avoiding selection bias (Hughes et al., 2014).

This dataset gives the resulting data collation for comparative-control impact studies. We collated data from 41 studies that compared the benthic biota in trawled areas with those in control locations (that were either not trawled or trawled infrequently).