The sperm whale (Physeter macrocephalus) Mediterranean subpopulation was recently proposed for listing as endangered, following the criterion C2a(ii) which refers to “population size estimated to number fewer that 2500 mature individuals and either; a continuing decline, observed, projected, or inferred, in numbers of mature individuals and at least 95% of mature individuals in one sub population” .
In the study area the sperm whale’s presence was monitored since 1991. However, the IFAW detection acoustic system was set up only since 2004. As a consequence, the number of sightings raised significantly.
Sperm whale’s residency and movements within the study area have been regularly investigated using photo-identification data collected over a 8 years period (2003–2010).
A total of 50 individuals were photo-identified on the base of their natural marks on the fluke. Scars and marks, on both sides of the animals, as well as the shape of the dorsal fin, where useful tools to complete Photo-ID recognition especially when matching was uncertain, this information was added to the catalogue when available.
Data confirmed the presence of immature males’ units in the waters of the Canyon of Cuma, supporting the hypothesis that this area is relevant for all the species’ ages classes, with social units composed by females and their immature, lone males (bulls), and variable aggregations of immature males. This last association pattern is poorly known.
Our data suggest that between these young males a preferred long term association exist and so that the social structure of not reproductive males units could reflect that of female units regarding complex and long term relationships between individuals.
Monitoring the social structure and the status of the population will be a key for the conservation of the species in the Mediterranean Sea; a challenge for the sperm whale protection in the area is represented by the proposal of the enlargement of the Marine Protected Area of Ischia, Procida and Vivara (designed for the conservation of the critical habit of common dolphis) into a SCI (Site of Community Importance) including the whole Cuma canyon system and sperm whale’s critical habitat.