Large-scale assessments of bottom trawling effects on Vulnerable Marine Ecosystems can significantly under-represent impacts

Bottom trawling threatens Vulnerable Marine Ecosystems (VMEs). We evaluated historic benthic trawling impacts on 10 VME indicator taxa (e.g. cold-water corals) and estimates of VME distribution (based on the overlap of taxa abundance-based and richness-based indices) across New Zealand waters, using a dynamic Relative Benthic Status model, incorporating 30 years of fishing data, and taxon-specific depletion and recovery rates. The analysis was conducted at a national scale and within six ecologically relevant bioregional scales. We predicted severe, lasting impacts at bioregional levels, despite modest national-scale effects. All VME indicator taxa fell below an 80% 'good ecosystem state' threshold in at least one bioregion, with VMEs in three of six bioregions below this critical limit. Combined with limited observed recovery for these taxa 20-40 years post-fishing, these impacts likely represent Significant Adverse Impacts. By integrating high-resolution spatial predictions with long-term impact assessments at ecologically relevant scales, our approach provides a novel replicable framework for regional and global assessments, identifying pristine areas vital for conservation under agreements like the High Seas Treaty. This study is an important step towards sustainable fisheries management and marine biodiversity conservation, providing essential insights to guide policy decisions and protect the oceans' most vulnerable ecosystems from bottom trawling.