Aspects of the distribution of Cuvier's beaked whale (Ziphius cavirostris) in relation to topographic features in the Pelagos Sanctuary (north-western Mediterranean Sea)

Abstract

Cuvier's beaked whale is a poorly-known species. It has been considered common since 1980 in the Pelagos Sanctuary (north-western Mediterranean Sea), but it has hardly been studied, chiefly due to difficulties in sighting. Stranding data indicates that the beaked whale is present all along the Ligurian coast. As with any deep-diving odontocete, Cuvier's beaked whale feeds mostly on deep-sea squid, but also on some fish and a small number of crustaceans. As a consequence, it is thought to be found mainly in waters deeper than 1000 m, where the sea bed has a particular slope. The aim of this work is to analyse a large quantity of sightings in order to define the favoured habitat of the beaked whale. Topographic features such as depth, depth gradient and bathymetric anomaly were analysed due to their direct influence on the prey of Cuvier's beaked whales. Data were registered between Genova and Imperia, from 2000 to 2006. Two hundred and forty-seven sightings were recorded, a total of 532 whales. The mean herd size observed was 2.3±1.5 (range=1–11). For 40 sightings, the group composition was divided into maturity categories, using results obtained by photo-identification. Seventeen groups consisted of purely immature animals, and 4 groups consisted of only mature animals. The 19 mixed herds were composed mainly of 4.0±2.2 individuals (range=2–8) and consisted of 58% mature individuals. The 17 immature groups consisted of 2.1±0.9 individuals. Mature animals were usually found alone. Forty-eight per cent of beaked whales were seen where the depth was between 756 and 1389 m but the encounter rate was higher between depths of 1389 and 2021 m. The sightings were more frequent (34%) where the sea floor slope was between 31 and 51 m/km but the encounter rate was higher where the sea floor slope was between 11 and 31 m/km. The encounter rate for Cuvier's beaked whales was higher where the depth anomaly was positive with values between 342 and 586 m.

Habitat preferences of two deep-diving cetacean species in the northern Ligurian Sea

“…In the Pelagos Sanctuary, Cuvier's beaked whale exploits the upper and lower slopes along the Ligurian−Provençal coast, at depths ranging from 1000 to 2500 m (Azzellino et al 2008, Moulins et al 2008, showing preference for areas with complex topography (Moulins et al 2007, Gannier & Epinat 2008, Azzellino et al 2012. Similar habitat preferences have been found for the sperm whale, whose preferred habitat lies in the canyons in the slope area (Gannier et al 2002, Moulins et al 2008, Praca et al 2009, Azzellino et al 2012.…”

“…Many studies demonstrate how these datasets, when collected following an ad hoc protocol and/or analyzed taking into account potential sources of bias, can be a valuable resource for understanding species distribution. Whalewatching data sets have previously been used to characterize ceta cean habitats within the Pelagos Sanc tuary (Azzellino et al 2001, 2008, Moulins et al 2007.…”

“…The first dataset was collected on board whale-watching vessels operating in the Ligurian Sea from 2004 to 2007, from different operators and from April to October each year. These whale-watching vessels had previously been used as nondedicated plat forms for carrying out cetacean research (Moulins et al 2007(Moulins et al , 2008. As a consequence, a strict protocol for data collection was al ready in place and was followed on each vessel.…”

Risk mapping for sensitive species to underwater anthropogenic sound emissions: Model development and validation in two Mediterranean areas

“…All cetaceans regularly observed in the Mediterranean Sea, including seven species of odontocetes (Cuvier's beaked whale (Z. cavirostris), striped dolphin (Stenella coeruleoalba), Risso's dolphin (Grampus griseus), sperm whale (Physeter macrocephalus), long-finned pilot whale (Globicephala melas), common bottlenose dolphin (Tursiops truncatus), shortbeaked common dolphin (Delphinus delphis)) and only one species of mysticete, the fin whale (Balaenoptera physalus) are found in this region. The Gulf of Genoa in the Ligurian Sea was found to be a key area in the western Mediterranean Basin since Cuvier's beaked whales have been regularly observed at sea (Azzellino et al, 2008;D'Amico et al, 2003;Macleod and Mitchell, 2006;Moulins et al, 2007). The Gulf of Genoa is characterized by several canyons with very steep slope gradients extending from the shelf break to a depth of about 1200 m. The Genoa canyon region (Fig.…”

“…Several studies have, in fact, reported beaked whales as regularly observed over the continental slope in waters 200-2000 m depth, (Hamazaky, 2002;Hooker et al, 2002;MacLeod and Zuur, 2005;Waring et al, 2001) and near submarine canyons (Wimmer and Whitehead, 2004). In the Mediterranean Sea, Cuvier's beaked whale presence has been found associated with the continental slope area and submarine canyons (Azzellino et al, 2008;Cañadas et al,2002;D'Amico et al, 2003;Gannier and Epinat, 2008;Moulins et al, 2007). This was another reason for trying a ''validation'' exercise using bathymetry as predictor for this species.…”