Marine reserves are increasingly advocated not only as conservation but also as fisheries management tools to safeguard the decline of coastal fishing resources. Still, conclusive evidence of their functioning is lacking, amongst others due to the influence of spatio-temporal variations in fish populations and habitat heterogeneity which could hamper a sound data interpretation. We conducted a spatial analysis of the benefits of the Medes Island Marine Reserve by combining geostatistical and Geographic Information System (GIS) tools. Concurrently, we analysed effects of trends reflecting habitat heterogeneity and spatial structuring of data on spatial predictions of fish catch per unit effort (CPUE) and length. Predicted spatial patterns showed the complexity and simultaneous action of trend factors leading to mostly non-linear gradients in CPUE and length data. CPUE of total fish and CPUE and length of common pandora (Pagellus erythrinus) increased close to the Integral Reserve due to direct and indirect reserve effects. CPUE and length of striped red mullet (Mullus surmuletus) slightly increased also near the Integral Reserve, but distinct reserve effects could not be identified due to the strong influence of artificial reefs. We conclude that the spatial dimension of the Buffer Zone, where artisanal fisheries are allowed, permits in general protection only for target species, favouring a habitat with no discontinuities from the reserve outwards. Our spatial approach to assess reserve benefits provides major insights into complex systems like coastal marine reserves in the northwestern Mediterranean. In addition, it contributes to a crucial aspect of marine conservation, viz. the decision on the spatial dimension of protected areas

This study has been partially funded by the European projects BIOMEX (Contract No. QLRT-2001-00891) and EMPAFISH (Contract No. 006539). We thank Prof. Mikel Zabala and Miquel Secanell for helpful comments on data interpretation and data collection. The fishermen association and Nuria Muñoz, director of the Medes Island Marine Reserve, are acknowledged for their collaboration in this study. We thank two anonymous referees who helped to improve an earlier version of the manuscript. The first author was sponsored by a research fellowship of the German Research Foundation (DFG)

13 pages, 9 figures, 4 tables

Peer reviewed