Fin whale - Demographic models - commonly used in animal and plant populations - have been applied to marine mammals and cetaceans only in the recent years. Usually, two different approaches are used when dealing with demographic studies, based on static or cohort life-tables. A third approach refers to the use of mortality tables and provides detailed information about size⁄age and sex of dead individuals. This approach, based on stranding data, has for the first time been applied to cetaceans in the Mediterranean Sea, developing a demographic model for the Mediterranean fin whale population based on a life-history table (mortality table) using stranding records (Arrigoni et al., 2011). Dealing with stranded data implies several assumptions; the main one being that stranding data represent a faithful description of the real mortality by different life stages. This assumption, however, is true only if the probability of stranding is equal in all life stages.
This preliminary study described the structure of the Mediterranean sub-population by analyzing stranding records from the period 1986–2007, showing a strong impact, natural and anthropogenic, on calves and immature animals. These results, while confirm a common pattern to several mammals – characterized by high mortality in the youngest age classes - may prevent reaching sexual maturity, thus severely impacting the species at the population level. Proper conservation plans should therefore consider the discovery of breeding grounds, where calves may benefit from greater protection, to increase survival rates. Similarly, appropriate naval traffic regulations, aimed at reducing mortality rates from ship collisions, could enhance the survival of mature females and calves. In addition, mitigating other sources of mortality and stress, such as chemical and acoustic pollution, whale-watching activities and habitat loss and degradation, could further improve the population’s chances of survival.
Common bottlenose dolphin - The only Mediterranean area with quantitative historical information that can be used to infer population trends over time scales of more than a couple of decades is the northern Adriatic Sea. There, bottlenose dolphin numbers likely declined by at least 50% in the second half of the 20th century, largely as a consequence of deliberate killing initially, followed by habitat degradation and overfishing of prey species. For some other parts of the northern Mediterranean, e.g. Italy and southern France, the available information is less precise but suggests similar trends. In an area off southern Spain where the species has been studied intensively, abundance estimates have shown variability but no trend since the early 1990s.
Since there are no historical data on the density and abundance of bottlenose dolphins in the Pelagos Sanctuary, it is not possible to infer possible increase or decrease over time. The Groupe d’Etudes des Cétacés de Méditerranée has estimated – through direct counting and photo‐identification - around 198–242 bottlenose dolphins around the island of Corsica in 2000, and 130–173 in 2003. These estimates appear to be lower than those assessed through mark recapture analysis in the same area in 2006, but any inference on potential trends is purely speculative, as a different approach has been used to for these estimated and this may lead to significant biases.