The susceptibility of sensitive species through analysis of their distribution and the overlap with relevant fishing effort distribution: SMRU Contribution to the DefineIt Final Report

The population sizes and estimates of sustainable take limits for the most numerous species of seabird and marine mammal have been collated for the North Sea. All available bycatch rate data have also been compiled to provide a quantitative overview of the vulnerability of each species to each gear type for which observer data are available. Certain species and gear combinations occur much more frequently than others. Specifically harbour porpoises, seals and guillemots are frequently recorded in static nets, while longline fisheries have relatively high rates of bycatch for fulmars and kittiwakes. The data collated are not necessarily representative of all North Sea fisheries, and sampling biases are noted. Nevertheless, when the observed bycatch rates are compared with a crude index of overall fishing effort for static nets, it is possible to see which species are most likely and least likely to be subject to unsustainable levels of annual removal.
Using distribution data from a long term sightings database, together with STECF data on the spatial distribution of fishing effort within the North Sea, it has also been possible to explore the susceptibility of several species to bycatch in specific gear types. A method of calculating and displaying risk of bycatch is developed, and 25 maps of species distribution (summer and winter for bird species) are presented as guides to where further monitoring and / or mitigation measures might best be focused.