Movement, ranging patterns and habitat use of Indo-Pacific humpback dolphins (Sousa chinensis) in the Langkawi Archipelago and adjacent Perlis-Kedah coastal waters, Malaysia

Abstract

1. Studies on the ranging patterns and habitat use of Indo-Pacific humpback dolphins (Sousa chinensis) in Southeast Asia are scarce but essential to inform conservation and management of a species known to be susceptible to anthropogenic pressures. 2. This study is the first to investigate the long-term movement, range sizes and habitat use of humpback dolphins in the Langkawi Archipelago and adjacent Perlis-Kedah mainland coast of Malaysia using boat-based photo-identification surveys conducted between 2010 and 2020. 3. A total of 669 humpback dolphin individuals were identified, making it one of the largest photo-ID catalogues within their geographic range. Lagged identification rates suggested that some individuals maintained long-term site fidelity in the study area. 4. Low transition probabilities and 194 photo-identification matches revealed humpback dolphins moved minimally between Langkawi and the adjacent Perlis-Kedah mainland; however, most southward dolphin movements did not extend beyond Kuala Jerlun in northern Kedah. 5. The mean range sizes estimated for 16 regularly sighted individuals through minimum convex polygon and kernel density estimate 95% utilization distribution were significantly different, at 338.2 ± 183.8 and 75.6 ± 28.6 km2, respectively. 6. Most individual and population core areas (i.e. kernel density estimate 50% utilization distribution) overlapped with core feeding and nursery grounds in shallow coastal and estuarine waters (i.e. <10 m deep and <1.3 km from the coastline). 7. Dolphin range size and spatial use patterns were probably linked to prey distribution and availability (i.e. influenced by environmental factors such as habitat features) and social groupings and dynamics. 8. These findings inform science-based recommendations for habitat management, including implementing restricted areas from coastal development, vessel speed-limit zones and boating codes-of-conduct, to minimize anthropogenic impacts and support sustainable coastal development in the binational Satun-Langkawi Important Marine Mammal Area.