Long-term trend analysis of deep diving cetacean species occurring in the Pelagos Sanctuary (Northwestern Mediterranean Sea).

Several threats are known to affect cetacean species and their habitats in the Mediterranean sea, most of them being related to human activities. To enforce effective mitigation actions, extensive knowledge of cetacean ecology is required. In this study a 23-year sighting series (1990-2012) of sperm whale (Physeter macrocephalus), Risso’s dolphin (Grampus griseus) and Cuvier’s beaked whale (Ziphius cavirostris) was analysed to assess temporal patterns or trends in their presence in the Pelagos Sanctuary area. Sighting data were collected by Tethys Research Institute (n= 434) and CIMA research Foundation (n= 142) during shipboard surveys conducted between 1990-2012 and 2004-2012, respectively. This effort yielded a total of 576 sightings: 289 sperm whales, 164 Risso’s dolphins and 123 Cuvier’s beaked whales. For the purpose of the analysis a grid of 6.8 x 9.3 km cell units was created and used for the spatial analysis. The species’ encounter rate variability in time was analysed through a General Linear Model approach, which revealed the existence of a significant increasing trend (P<0.05) for sperm whales and Cuvier’s beaked whales presence in the area. Contrarily, no trend was found for Risso’s dolphin. This study provides evidence that the animal distribution in the Pelagos Sanctuary is affected by some drivers of change. Changes may be due to a wide range of causes (i.e. prey availabilities, climate change, noise). The correlation of the results obtained with this long term trend analysis with the available time series of environmental variables (i.e. Sea Surface Temperature from remote sensing) and anthropogenic pressure affecting the area (i.e. maritime traffic, fishing activities) will provide essential information to evaluate the implications of the different factors of variability and their possible interactions in order to support appropriate management and conservation strategies.