Abstract
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.
Highlights
Understanding the patterns of spatial distribution of wild populations is a critical consideration in the development of effective management and conservation strategies [1]
In the Mediterranean Sea, a semi-enclosed highly biodiverse basin, where more than 90% of the harvested stocks are overexploited mostly due to a un-selective exploitation pattern [3, 4] and opportunistic fishery behaviour [5], the protection of the main nurseries of commercial species is increasingly viewed as a major step toward the achievement of more sustainable exploitation patterns
Due to poor enforcement and reduced trawl selectivity, some sectors show up to 70% of the catch of specimens below the minimum conservation reference sizes (MCRS) [4]. Such an exploitation pattern is hindering the achievement of Maximum Sustainable Yield (MSY) for fisheries, as required both by the new European Common Fisheries Policy (CFP) and the EU Marine Strategy Framework Directive (MSFD), as well as the maximisation of fleet revenues [3], [4]
Summary
Understanding the patterns of spatial distribution of wild populations is a critical consideration in the development of effective management and conservation strategies [1]. Nagelkerken et al, [2] have provided a valuable step forward in the process leading to the identification and management of critical nursery areas by focusing on the identification of highly productive patches, especially in situations where large habitat units cannot be protected as a whole due to socio-economic, practical or other considerations This is a common situation in the Mediterranean Sea, where nurseries of commercial demersal species often are distributed in offshore habitats such as the shelf break, covering large extensions of the sea bottom. The temporal persistence of the characteristics of an area is a fundamental prerequisite for its inclusion in a conservation network, as commonly considered in terrestrial ecosystems [31] Based on these assumptions, we adopted a 6-step approach to identify and classify nursery areas of commercial species for conservation purposes. (6) we calculated the spatial overlap between nursery areas and the current fisheries restricted areas as a basis for the implementation of spatial conservation planning for demersal fisheries resources in the North Mediterranean Sea
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