From science to policy-a geostatistical approach to identifying potential areas for cetacean conservation: a case study of bottlenose dolphins in the Pelagos sanctuary (Mediterranean Sea)

Cetaceans are top-level predators that serve as sentinels of the health and status of lower trophic levels in the marine ecosystem. For this reason they attract significant attention in marine conservation planning and often have been used to promote designation of reserve areas in many countries (e.g., Ligurian Sea, Moray Firth, Hawaiian Islands, The Gully, Wadden Sea, Banks Peninsula, and Golfo San Jos,). Many policies are designed to protect cetaceans. For example, the Habitat Directive requires member states to select, designate, and protect sites that support certain natural habitats or species, such as the bottlenose dolphin, as Special Areas of Conservation (SACs) that aim to create a network of protected areas across the European Union known as Natura 2000. The boundaries of protected areas for cetacean species must be defined for management purposes. In recent years, many techniques have been developed to define the distribution of cetaceans in relation to habitat preferences. Although these models can provide an understanding of the ecological processes that determine species distribution, their application requires prior knowledge of the variables that should be included in the model, the interactions among these variables, and their effects on species distribution. Thus, the lack of available data in understudied areas precludes the application of these types of models. As an alternative, we describe a geostatistical approach to identifying areas that potentially should be designated as marine protected areas for cetaceans. We illustrate the application of the kriging algorithm to the bottlenose dolphin population that resides in the northwestern Mediterranean Sea. The data derived from a 7-year survey were used. The encounter rate is the only variable required for this method, making it very easy to apply. The resulting georeferenced and high resolution map includes areas most visited by bottlenose dolphins, which are called core areas. Core areas are helpful for establishing the boundaries of marine reserves for the protection of the species. The approach described herein is accurate, precise, unbiased, replicable to all highly mobile species and easy to understand by both researchers and policy makers.