Breves periodos de ausencia del calderón común Globicephala melas (Traill, 1809) en el Estrecho de Gibraltar

Abstract

Long-finned pilot whales Globicephala melas (Traill, 1809) are resident in the Strait of Gibraltar. Because of their predictable presence and distribution, they account for most of the sightings and represent the main target for whale-watching operators. Nevertheless, these groups have been reported to disappear for one or two weeks each summer, possibly because of increased disturbance due to the presence of sportfishing vessels and whale-watching operators in the area. Our research was conducted in the Strait of Gibraltar from an opportunistic whale-watching platform, from April to October every year from 2003 to 2006. Large numbers of offspring were observed in a great number of sightings. Newborns were present throughout the entire sighting season. Group size decreased just before the disappearance of the pilot whales. The Strait of Gibraltar has very strong currents and winds and supports intense maritime traffic. Additionally, interactions between long-finned pilot whales and killer whales (Orcinus orca) in the Strait of Gibraltar have recently been described, the former chasing the latter. The period during which long-finned pilot whales disappeared in 2003 and 2004 coincided with the arrival of killer whales in the Strait of Gibraltar, but not in later seasons. We postulate that the majority of, or the entire long-finned pilot whale population, moves from the Strait of Gibraltar during this period to the calmer and safer waters of the Alboran Sea to give birth. However, we do not rule out the possibility that the presence of killer whales may influence the absence of pilot whales directly or in combination with the other factors described above.