Bittau, Luca (2014) Pelagic cetaceans off North-Eastern Sardinia and implications for conservation. Doctoral Thesis.
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The all-year-round knowledge on cetaceans off Sardinia is scarce and mostly focused on the coastal species Tursiops truncatus in the northern waters of the island. This work aims to increase information on pelagic cetaceans in the poor studied off-shore waters from North-Eastern Sardinian coast on the basis of surveys carried out between 2010 and 2013, using dedicated and opportunistic surveys.
First I evaluate the occurrence of pelagic cetacean species, the spatial-temporal distribution and the interactions with fixed physical variables (depth, slope and shape), non-fixed environmental variables (Sea Surface Temperature and chlorophyll a) which may affect their presence and distribution in the study area. The relative abundance of the cetacean species regularly inhabiting the area and the high encounter rate values, point out the significance of the Caprera Canyon for the cetaceans’ conservation, in the central Tyrrhenian Sea. Therefore I analyzed the occurrence and seasonal distribution of Balaenoptera physalus the only Mysticete in Mediterranean Sea, in relation with oceanographic variables as Sea Surface temperature and chlorophyll a. The high seasonal presence of fin whale off north-eastern Sardinia reflects a yearly pattern and is linked to a mix of variables such as the bottom features, water circulations as proxy of prey availability.
Moreover, I analyzed the sightings of three social units of Physeter macrocephalus recorded during summer 2010 and 2013. The encounter rates of this species in the entire study period were low. Despite this I recorded three encounters with sperm whale pods that highlighted the periodic use of the Caprera Canyon by these large cetaceans. The social units were composed of several individuals such as females, calves and probably young males. Finally I present the first documented records of a free-ranging Sowerby’s beaked whale (Mesoplodon bidens) in the Mediterranean Sea. This rare and elusive cetacean was sighted together with three Cuvier’s beaked whales in a mixed species group. Scarring observed on the whale’s flanks may result from interspecific interaction with males of Cuvier’s beaked whales. Nevertheless, all the gathered data suggest that the mesoplodont in the Tyrrhenian Sea could be considered as a stray.
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