NON‐LETHAL SHARK ATTACK ON A BOTTLENOSE DOLPHIN (TURSIOPS SP.) CALF

Abstract

The risk of predation by sharks is considered to have a strong influence on dolphin behavior, especially group formation and habitat use (Heithaus 2001a). Although evidence of shark attacks on dolphins abounds (in the form of shark bite scars, shark stomach contents, etc.), there have been no published reports in which researchers have directly observed a shark attack on a dolphin in the wild. There are, however, several reports of calves that have died from shark-induced wounds and cases in which researchers have been able to obtain statements from witnesses following a lethal shark attack (e.g., Wood et al. 1970, Mann and Barnett 1999). Here, I document the response of a group of bottlenose dolphins (Tursiops sp.), containing adult and juvenile females and calves, to the attack of one of its group members (a 3.5-mo-old calf) by an unidentified shark. Because the attack occurred during a focal follow of one of the mother-calf pairs in the group, I present a detailed description (derived from systematic observational data) of the behavior of the focal mother-calf pair, in addition to a description (based on ad libitum sampling) of other group members’ behavior prior to and following the attack. The observations occurred offshore of Monkey Mia in Shark Bay, Western Australia (25◦47′S, 113◦43′E). The study population consists of over 600 individually recognized bottlenose dolphins (Tursiops sp.). The three mother-calf pairs present during the described attack are part of a longitudinal study in which focal follows have been conducted on individual mother-calf pairs each year since 1988 (Mann and Smuts 1998, Mann and Watson-Capps 2005). During follows, systematic data collection is achieved using a combination of point, continuous, scan, and ad libitum sampling (see Altmann 1974). Information recorded includes focal mother and calf activity, mother-calf distance, group composition, and other information. Group membership