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Key Oceanographic Characteristics of Cuvier’s Beaked Whale (Ziphius cavirostris) Habitat in the Gulf of Genoa (Ligurian Sea, NW Mediterranean)

Lanfredi C, Azzellino A, D’Amico A, Centurioni L, Rella MA, Pavan G and Podestà M

Cuvier’s beaked whale presence has been associated worldwide with continental slope and submarine canyons areas. In the Mediterranean Sea, a hot spot of the species presence has been identified in the Genoa Canyon area, located in the Gulf of Genova (Ligurian Sea, NW Mediterranean Sea). Within the framework of the NATO Marine Mammal Risk Mitigation Project, several research cruises have been conducted between 1999 and 2011 in the Ligurian Sea area. During these cruises depth profiles of temperature, salinity, sound velocity, dissolved oxygen, fluorescence and turbidity as a function of depth were collected using a Conductivity, Temperature, Depth (CTD) and auxiliary sensors installed on a Rosette frame. Concurrently, Cuvier’s beaked whale (Ziphius cavirostris) presence was assessed through visual observations. The aim of this study was to investigate the environmental characteristics of a beaked whale habitat in the Genoa canyon area correlating beaked whale presence with the oceanographic variables. A Logistic Regression model was developed using the data collected during the oceanographic campaign carried out in summer 2002. Model accuracy was also evaluated in the same area based on the data collected 9 years later in summer 2011. The depth of the maximum dissolved oxygen (Depth Ox Max) turned out to be a significant predictor of beaked whale presence in the studied area. Higher presence probabilities of beaked whales were found associated to higher turbidities of deep-water layers in both the calibration and evaluation set. Results suggest dynamic predictors may act as proxy of macro-scale features that characterise beaked whale habitats. Particularly the depth the maximum oxygen concentration may be a tracer of the vertical exchanges of water masses (i.e., downwelling), transferring energy from the surface waters to the deep waters where beaked whales feed on their prey.