MEPS 237:301-305 (2002)  -  doi:10.3354/meps237301

Diving and night-time behavior of long-finned pilot whales in the Ligurian Sea

Robin W. Baird1,*, J. Fabrizio Borsani2, M. Bradley Hanson3, Peter L. Tyack4

1Biology Department, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
2Istituto Centrale per la Ricerca Applicata al Mare, via di Casalotti 300, 00166 Roma, Italy
3National Marine Mammal Laboratory, 7600 Sand Point Way NE, Seattle, Washington 98250, USA
4Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
*Present address: NOAA, NMFS, 101 Pivers Island Road, Beaufort, North Carolina 28516, USA. E-mail:

ABSTRACT: Pilot whales Globicephala spp. have long been thought to be deep divers, yet little information is available on dive depths. During August 1999 we obtained detailed dive data from suction-cup-attached time-depth recorder/VHF radio tags deployed on 5 long-finned pilot whales G. melas. Pilot whales were tagged for short periods (average 5 h ind.-1) in deep (>2000 m) waters of the Ligurian Sea, off the NW coast of Italy. During the day all 5 whales spent their time in the top 16 m of the water column, and visible surface activities consisted primarily of rest and social behaviors. Tags remained attached after dark on 2 whales and shortly after sunset both whales made several deep dives (max. 360 and 648 m). Velocity on these deep dives was greater than during shallow dives either during the day or at night, suggesting that these deep dives function primarily for foraging. Our results confirm the supposition that long-finned pilot whales can dive deep, particularly within 2 h after sunset, which is the time that vertically migrating prey become more readily available as they move closer to the surface.

KEY WORDS: Diving · Foraging · Globicephala · Pilot whale · Diel behavior

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