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Wild and captive delphinids are known to carry animate and inanimate objects on their rostra, melons, fins and tail flukes. Captive bottlenose dolphins (Tursiops spp.) and pilot whales (Globicephala spp.) will often carry random objects such as seaweed, fish, and plastic toys in their tank (Brown and Norris 1956, Caldwell 1956, Tizzi et al. 2000). Free ranging bottlenose, Hector’s (Cephalorhynchus hectori, van Beneden 1881), and Atlantic spotted dolphins (Stenella frontalis, Cuvier 1829) have been observed carrying seagrass, fish, sea cucumbers and pieces of coral among others (Slooten and Dawson 1994, Mann and Smuts 1999, Miles and Herzing 2003). Most of these object carrying events are thought to be related to animal play: the motor activity directed towards the object appears to provide no obvious direct benefit to the individual(s) involved (Martin and Caro 1985). The only object manipulation activities that have been suggested as non-play in delphinids are: 1) carrying of dead calves, and 2) sponge carrying by some bottlenose dolphins in Shark Bay, Western Australia. The carrying of dead calves has been hypothesised as a manifestation of epimeletic (care-giving) behaviour (Harzen and Santos 1992, Lodi 1992, Fertl and Schiro 1994, Palacios and Day 1995). Sponge carrying by bottlenose dolphins in Shark Bay has been identified as a foraging specialisation involving tool-use (Smolker et al. 1997). It is believed that the animals involved use sponges to protect their rostrum from shells, rocks and spines and stingers from noxious organisms while looking for prey in the sea bottom. Genetic and ecological data indicate that the use of sponges as tools is culturally transmitted mainly within a matriline (Krützen et al. 2005). The use of sponges as a foraging tool has not been described in any other population of bottlenose dolphins or dolphin species, although anecdotal evidence suggests that humpback dolphins in the Dampier Archipelago, Western Australia, also carry sponges (M.Krützen, personal communication, July 2007). Indo-Pacific humpback dolphins (Sousa chinensis, Osbeck 1765) are found throughout coastal waters of the Indo-Pacific region from the eastern shores of South Africa to the northern coast of Australia (Jefferson and Karczmarski 2001, Parra et al. 2004). Two cases of epimeletic behaviour involving humpback dolphins carrying dead calves have been observed in Hong Kong (Parsons 1998). In South Africa, humpback dolphins were seen carrying and throwing sea shells for short periods of time during social-play activities (Saayman and Tayler 1979). This paper describes a sponge carrying event by an adult Indo-Pacific humpback dolphin and discusses the potential functions of this behaviour in light of the observations made. The observations were made on November 9, 2006, during boat based surveys of coastal dolphins in the Hinchinbrook Channel (188169 S, 1468049 E), northeast Queensland, Australia. The Hinchinbrook Channel, part of the Great Barrier Reef World Heritage Area, is a 44km long tidal channel that separates Hinchinbrook Island from the mainland. The channel has a maximum depth of 20 m and is fringed by one of the largest mangrove forests in Australia. During dolphin surveys, systematic data collection was carried out through focal follows, photo-identification, and scan and ad libitum behavioural sampling. Further details of survey procedures are described by Parra (2006) and Parra et al. (2006). Four adult humpback dolphins were sighted at 08:43 and followed for 2.3 h at distances ranging from 10 to 40 m. Observations took place in waters ranging from 5.1 to 9.4 m deep (means6.9, SDs1.3, ns28). The school changed later to three adults and a juvenile (see description below). All adults involved had distinctive marks on their dorsal fins. For most of the duration of the sighting, dolphins were predominantly travelling northwards slowly (2–3 km/h) within 10 m of each other. At 08:56 one of the dolphins surfaced with a large object on its rostrum (Figure 1). The object was dark brown in colour and covered the total length of the dolphin’s rostrum. At first sight the object looked like a marine sponge. Though the object could not be retrieved for further identification, Dr. John Hooper, an expert in sponge taxonomy with the Queensland Museum, inspected the sighting photographs and concluded that the object resembled a sponge-algal complex (referred to from now on as a sponge). The sponge appeared to be held in place by its apparent conformity to the shape of the rostrum and by the water pressure as the dolphin moved forward. For the next 5 min, the dolphin swam at the surface with the sponge on its rostrum following no specific direction and taking several breaths interspersed with short dives less than 1 min long. During this time the other three animals remained close to the sponger (-50 m). At 09:01 the dolphin per-

Observations of an Indo-Pacific humpback dolphin carrying a sponge: object play or tool use?