Distribution, abundance and seasonality of cetaceans sighted during scheduled ferry crossings in the central Tyrrhenian Sea: 1989-1992

The results of a medium-term survey of cetaceans in the central Tyrrhenian Sea, the first ever all-year-round one to be made in the Mediterranean, are reported. Individuals of Balaenoptera sp. were sighted throughout the year, although with significant seasonal differences, in agreement with the hypothesis of a resident population making seasonal migrations around, but remaining inside the Mediterranean Sea. Striped dolphins (Stenella coeruleoalba), the most frequently observed species, are present all year round with no significant seasonal differences. Some observations on the presence and group structure of bottlenose dolphins (Tursiops truncatus) and Cuvier's beaked whale (Ziphius cavirostris) are reported. Individuals of four other species (Physeter macrocephalus, Grampus griseus, Globicephala melaena and Delphinus delphis) were also sighted.