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The identification of nursery grounds and other essential fish habitats of exploited stocks is a key requirement for the development of spatial conservation planning aimed at reducing the adverse impact of fishing on the exploited populations and ecosystems. The reduction in juvenile mortality is particularly relevant in the Mediterranean and is considered as one of the main prerequisites for the future sustainability of trawl fisheries. The distribution of nursery areas of 11 important commercial species of demersal fish and shellfish was analysed in the European Union Mediterranean waters using time series of bottom trawl survey data with the aim of identifying the most persistent recruitment areas. A high interspecific spatial overlap between nursery areas was mainly found along the shelf break of many different sectors of the Northern Mediterranean indicating a high potential for the implementation of conservation measures. Overlap of the nursery grounds with existing spatial fisheries management measures and trawl fisheries restricted areas was also investigated. Spatial analyses revealed considerable variation depending on species and associated habitat/depth preferences with increased protection seen in coastal nurseries and minimal protection seen for deeper nurseries (e.g. Parapenaeus longirostris 6%). This is partly attributed to existing environmental policy instruments (e.g. Habitats Directive and Mediterranean Regulation EC 1967/2006) aiming at minimising impacts on coastal priority habitats such as seagrass, coralligenous and maerl beds. The new knowledge on the distribution and persistence of demersal nurseries provided in this study can support the application of spatial conservation measures, such as the designation of no-take Marine Protected Areas in EU Mediterranean waters and their inclusion in a conservation network. The establishment of no-take zones will be consistent with the objectives of the Common Fisheries Policy applying the ecosystem approach to fisheries management and with the requirements of the Marine Strategy Framework Directive to maintain or achieve seafloor integrity and good environmental status.

An analysis of 38 bottom trawl hauls at depths of 251–737 m off the Balearic Islands (western Mediterranean) during autumn 2002 and spring 2003 was used to compare the species and size selectivity of 40-mm diamond- and square-mesh codends under commercial conditions. There was no difference in the catch composition or the yield that could be attributable to mesh shape, although the percentage of total and commercial species discarded with a diamond mesh was higher than with a square mesh. At least in the short term, the escapement ratio and the economic loss with the diamond mesh were lower than with square mesh, but economic efficiency was no different between them. For all the main species compared, except one flatfish, size selectivity parameters were lower for the diamond-than for the square-mesh codend. Selectivity values for the one flatfish species were similar. From the results it is concluded that, within the context of precautionary management, introduction of a 40-mm square mesh in the codend could be an appropriate and plausible measure to improve the state of the resources exploited by the deepwater crustacean trawl fishery of the upper slope off the Balearic Islands, and to reduce the impact of the fishery on the ecosystem.

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