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Mills, C. M., Townsend, S. E., Jennings, S., Eastwood, P. D., and Houghton, C. A. 2007. Estimating high resolution trawl fishing effort from satellite-based vessel monitoring system data. – ICES Journal of Marine Science, 64: 248–255. High resolution estimates of trawling effort are needed to underpin studies of trawling impacts on species, habitats, and ecosystem processes, and to monitor responses to area closure and other management actions. Satellite-based vessel monitoring systems (VMS) were designed for fishery control and enforcement, but they provide potentially valuable source information on spatial and temporal patterns of trawling activity at multiple scales. Based on an analysis of VMS data for UK beam trawlers in the North Sea, a method is described for identifying trawling activity and estimating fishing intensity based on the minimum and maximum potential spatial extent of trawling effort from VMS data. The optimal method for identifying trawling and steaming behaviour combined speed and directionality rules and correctly identified trawling and steaming in 99% and 95% of cases, respectively. Using speed- and directionality-filtered VMS data, trawling effort can be reported as area impacted per unit time per unit area at a range of grid scales from 1 km to 100 km (10 000 km2). Trawling effort is accurately represented at a grid cell resolution of 3 km or less.

Summary 1.Species distribution modelling is an important and well-established tool for conservation planning and resource management. Modelling techniques based on central estimates of species responses to environmental factors do not always provide ecologically meaningful estimates of species-environment relationships and are being increasingly questioned. 2. Regression quantiles (RQ) can be used to model the upper bounds of species-environment relationships and thus estimate how the environment is limiting the distribution of a species. The resulting models tend to describe potential rather than actual patterns of species distributions. 3. Model selection based on null hypothesis testing and backward elimination, followed by validation procedures, are proposed here as a general approach for constructing RQ limiting effect models for multiple species. 4. This approach was applied successfully to 16 of the most abundant marine fish and cephalopods in the eastern English Channel. Most models were validated successfully and null hypothesis testing for model selection proved effective for RQ modelling. 5. Synthesis and applications . Modelling the upper bounds of species-habitat relationships enables the detection of the effects of limiting factors on species' responses. Maps showing potential species distributions are also less likely to underestimate species responses' to the environment, and therefore have subsequent benefits for precautionary management.

Eastwood, P. D., Mills, C. M., Aldridge, J. N., Houghton, C. A., and Rogers, S. I. 2007. Human activities in UK offshore waters: an assessment of direct, physical pressure on the seabed. – ICES Journal of Marine Science, 64: 453–463. Integrated assessments (IA) and marine spatial planning (MSP) are becoming major drivers for the assessment and management of human activities at sea. To be successful, both require an understanding of the distribution of the pressures caused by human activities. We used spatial data for the major human activities operating in the England and Wales sector of UK waters in 2004 to provide an assessment of direct, physical pressure on the seabed from multiple human activities. Pressure was estimated as the spatial extent of each of the activities; the intensity, longevity, and impacts arising from the pressures were not considered. Estimates of spatial extent were assigned to three pressure categories, subdivided into six pressure types. We estimated that four of the six pressure types affected < 1% of the seabed of England and Wales in 2004, whereas selective extraction caused by demersal trawling affected a minimum of 5.4%, rising to a possible maximum of 21.4%, of the total area of the seabed. This was a greater area than all other pressure types combined. The assessment process described here can be used as the framework for reporting human pressures at regular time intervals and feed into both IA and MSP for regional seas.

Density-dependent habitat selection has implications for fisheries management and for the recovery of depleted fish populations. According to ideal free distribution theory, populations contract into areas of highest habitat suitability as their abundance decreases. This can increase their vulnerability to fishing and predation. We detected density-dependent habitat selection by juvenile Atlantic cod (Gadus morhua) (ages 1 and 2) in the North Sea and compared the observed distribution–abundance relationships with those predicted from a model based on ideal free distribution theory and knowledge of optimal temperatures for growth, where temperature was used as a measure of suitability. As predicted by the model, in years when stock size was low, the catches were largely confined to regions with near-optimal bottom temperatures. Conversely, when population size was high, catches were spread across a larger area including regions with suboptimal temperatures. The spatial extent of optimal habitat appears to have decreased from 1977 to 2002, reflecting a gradual warming of the North Sea. The combined negative effects of increased temperature on recruitment rates and the reduced availability of optimal habitat may have increased the vulnerability of the cod population to fishing mortality.