Locomotor behaviours and respiratory pattern of the Mediterranean fin whale (Balaenoptera physalus)

Twenty-four Mediterranean fin whales were tracked in open sea with a method based on the assessment of the animal differential position in respect of the observer's absolute position aboard a vessel, with the concomitant recording of the respiratory activity. Short distance video recording was also performed in two whales, permitting the simultaneous determination of single breath expiratory (T_E) and inspiratory (T_I) durations. In the 24 whales swimming at an average velocity of 1.39 (0.47) m·s^–1 mean (SD), range: 0.62–2.44 m·s^–1], 2068 breaths organized in 477 respiratory cycles were observed. Each cycle entailed a prolonged apnoea dive phase 225 (91) s, T_dive) followed by a period near the surface 62 (28) s, surfacing], during which a series of breaths 4.6 (1.8)] was performed at short intervals. On the basis of track length and swimming velocity, two groups of animals were devised differing for convolution of the course (p<0.001), extension of ranging territory (p<0.01) and horizontal swimming velocity (p<0.05), which may represent two distinct behaviours. A possibly general mechanism of control of breathing in cetaceans was found, consistent with a model of constant tidal volume and variable respiratory frequency. Coherently with this model, T_E was independent of T_I or T_dive, in line with a passive expiration, while T_I appeared to be negatively correlated with T_dive (p<0.05), otherwise suggesting, similarly with terrestrial mammals, a significant role of hypercapnic stimulation. The estimated O₂ consumption of about 150 l·min^–1 is in line with the general allometric regression for mammals and corresponds to an energetic expenditure of 85–95 kJ·kg^–1·day^–1.Partially presented as a poster at The World Marine Mammal Science Conference and 12th Annual Conference of the European Cetacean Society, Monaco (Montecarlo), 20–24 January 1998.Angelo Colombini provided technical assistance.