Multiple sightings of large groups of Arnoux's beaked whales (Berardius arnouxii) in the Gerlache Strait, Antarctica

Abstract

On 5 May 2009, during the Multi-Scale and Interdisciplinary Study of Humpbacks And Prey (MISHAP09) cruise, a large group of socially active Arnoux’s beaked whales (Berardius arnouxii) was sighted in the southern-central region of the Gerlache Strait near the entrance of the Schollaert Channel between Brabant and Cuverville Islands, Antarctica (64◦33.9′S, 62◦37.1′W) (Fig. 1). Later, on 7 June 2009 in a similar location (64◦37.5′S, 62◦51.8′W), another sighting was made of a large group of Arnoux’s beaked whales. These represent two of the few confirmed sightings of this species in the nearshore waters around the Antarctic Peninsula, one of the only documentations of surface social activity, and the largest number of animals ever reported in a single group. At 1230 local time on 5 May, a large group of animals (approximately 60) was sighted 3 km from the ARSV LM Gould. The water depth around the whales was between 700 and 800 m. The first sighting cue was a series of short, bushy blows. As the ship approached, the animals became visible at the surface and were identified based on coloration, size, and shape of their head and melon, and rostrum shape. After the initial sighting, a second separate subgroup of animals (approximately 15) was sighted in the same area. Both groups of animals were traveling consistently to the southwest, deeper into the Gerlache Strait. Animals were seen surfacing quickly in close proximity to one another (<2 m), and often in physical contact with each other. During the course of the sighting we observed tail slapping by several individuals and three breaches. Photographs were obtained from an inflatable boat at a distance of approximately 100 m (Fig. 2). Several of the whales were visibly scarred with single or two parallel