Assessing the status of seabed habitats in trawled regions of the world

The impacts of bottom trawling on seabed habitats often are considered to pose serious environmental threats. Risk assessment can be used to evaluate these threats and to guide management regarding interventions needed to help... [ view full abstract ]

The impacts of bottom trawling on seabed habitats often are considered to pose serious environmental threats. Risk assessment can be used to evaluate these threats and to guide management regarding interventions needed to help meet sustainability objectives. We apply a simple quantitative method, applicable in data-limited situations, to assess seabed sedimentary habitats in 24 regions worldwide where bottom-trawl fishing occurs. The method estimates the relative benthic status (RBS) of the seabed: the amount of biota present, in equilibrium with bottom-trawling depletion, as a proportion of biota present without trawling. Estimating RBS for grid cells spanning a region requires few parameters: rates of recovery and trawl impact, and maps of fishing intensity and habitats. The overall status of regions is represented by the distribution of grid-cell RBS values and their mean, which are sensitive to trawling exposure and impact and recovery rates. Our assessment is currently a work-in-progress. Preliminary estimates indicate that most regional RBS values are greater than 90% (i.e. trawling has depleted regional biota by <10%) whereas few regions had RBS <70%. This assessment places trawling impacts in regional landscape perspective and provides world-wide comparisons for guiding management of environmental risks from trawling. A range of management interventions are possible to reduce these risks but may require trade-offs against food security priorities. Decisions about such trade-offs will vary among countries depending on the relative balance of environmental, social and economic priorities and costs of alternative interventions. RBS can assist by quantifying the environmental benefits of any alternative management strategies.