Cetacean occurrence and spatial distribution in the central Mediterranean Sea using ferries as platform of observation

While cetacean distribution and habitat is well investigated in some areas in the Mediterranean, only a few studies have been conducted so far in the central part of the Mediterranean basin. In order to fill this gap, a dedicated research program has been developed using ferries operating between Tunis and Genoa as platforms of opportunity to collect data on cetacean presence and distribution. The area was subdivided in three sub-regions: the Sardo-Tunisian channel, the eastern Sardinian margin and the international sanctuary for marine mammals Pelagos. During fall 2013, marine mammal observers surveyed 1900 nautical miles and recorded 39 encounters of 5 identified species including balaenopteridae, delphinidae, ziphiidae and physeteridae families. Bottlenose dolphin (Tursiops truncatus) and striped dolphin (Stenella coeruleoalba) were the most common species followed in decreasing occurrence by fin whale (Balaenoptera physalus), Cuvier's beaked whale (Ziphius cavirostris) and sperm whale (Physeter macrocephalus). The distribution of bottlenose dolphin was restricted to the shallow waters of the Tunisian plateau over the continental shelf. Striped dolphins were sighted in the open sea waters and the eastern Sardinia margin. Large cetaceans as sperm whale and fin whale were mainly recorded over the canyon of Bizerte in the Sardo-Tunisian channel. Highest diversity index was reported in the Pelagos sanctuary even during autumn, confirming the area as a preferred habitat for several cetacean species. Our results also highlight the importance of the Sardo-Tunisian channel, where a relatively important diversity index has been computed, especially over the canyon of Bizerte. This study is the first to investigate cetacean diversity in pelagic central Mediterranean waters and highlights the insistent need to develop regular monitoring in this area.