Boat Effects on the Behaviour of Indo-Pacific Humpback (Sousa chinensis) and Irrawaddy Dolphins (Orcaella brevirostris) in Cowie Bay, Sabah, Malaysia

A series of boat surveys were conducted from April to September 2008. This work evaluated the effects of boats on Indo-Pacific Humpback and Irrawaddy dolphins. The types of boats, dolphins’ interactions towards various types of boat and vessel-dolphin distance under different intensities were measured. The absence of boats sailing in the bay was considered as control situation. There was a highly significant difference in the response of Indo-Pacific Humpback (x2 = 97.1, df = 8, p = 0.000) and Irrawaddy (x2 = 52.4, df = 8, p = 0.000) dolphins to different classes of boats. Analyses showed that positive behaviour was the most observed behaviour towards trawlers for both dolphin species. However, Indo-Pacific Humpback (H = 3.107, p = 0.540) and Irrawaddy (H = 4.208, p= 0.379) dolphins independently associated with negative behaviour while interacting with all boat classes. Irrawaddy dolphin tend to avoid boats using outboard