How adequately are the critically endangered Balearic Shearwaters protected by the Special Protection Areas (SPAs) for seabirds? A case study in the Gulf of Cadiz

Abstract

The expansion of marine protected areas in pelagic areas has been crucial to achieve sufficient protection of the oceans. However, there is still some controversy about whether these protected areas actually cover the vital areas for some species. We investigate the summer distribution of the critically endangered Balearic Shearwater and its overlap with the Special Protection Area for seabirds (SPA), using the Gulf of Cadiz as a case study. This area holds the SPA named Marine Area of Gulf of Cádiz, covering 2314.2 km2. A dataset of nine years of vessel-based surveys between 2006 and 2017 was analysed, using Kernel Density Estimation to generate the core area polygons for each year. The area located off the Bay of Cádiz, southeast of the mouth of the Guadalquivir, has revealed as a very consistent key area for this species during summer. This area, covering 1082 km2, regularly hosted populations that exceeded the threshold for area of international importance (IBA criteria) for the species. The current SPA covers less than 40% of this new key area. The limitation in the number of years of monitoring and seasonal differences in the dataset used to establish the boundaries of the current protected area may be at the base of these discrepancies. This study emphasizes the importance of synthesizing and collecting long-term information to define marine protected areas and to assess their efficiency over the time. Furthermore, our study highlights the urgent need to expand this marine protected area to protect effectively this critically threatened species. Keywords: Balearic shearwater, Marine protected areas, Gulf of cadiz, Kernel density estimation, Long-term survey, Adaptive management