From August 2010 to December 2013, field photo-identification surveys were conducted to explore the social organization and distribution patterns of a threatened Indo-Pacific humpback dolphin (Sousa chinensis) population in Xiamen Bay, China. Out of 58 photo-identified dolphins, 56 dolphins that were sighted at least 2 times were used for social structure analysis. The association pattern among individuals was divided into 2 discrete communities with strong geographic adherence: 27 dolphins assigned to an eastern community (EC) and 29 dolphins assigned to a western community (WC). Among the WC individuals, 9 dolphins formed mixed groups with EC individuals at Tongan Bay and the mouth of Tongan Bay, leading to low-level intercommunity association. The 50% kernel density estimate and minimum convex polygon of each community were calculated, with the core habitats presented here differing substantially from those reported in previous studies. We propose that the geographical segregation of these 2 communities and the apparent shift in core habitats could be the result of adaptation by dolphins to local environmental conditions, notably intensive anthropogenic activities.

Monthly field surveys were conducted between August 2010 and July 2015 to explore seasonal group characteristics and occurrence patterns of Indo-Pacific humpback dolphins ( Sousa chinensis ) in Xiamen Bay, China. Dolphins formed larger groups in winter and spring (dry seasons) than in summer and autumn (wet seasons; U = 1,564.00, P < 0.001). Sighting encounter rates were higher during the wet season than during the dry season ( U = 181.00, P < 0.001), while individual encounter rates were not significantly different between seasons ( F = 0.494, d.f. = 3, P = 0.688). Dolphin sightings and the foraging events were mainly found in inner harbors (Western Harbour and Tongan Bay) during the dry seasons and in peripheral areas (Jiulong River Estuary, Wuyu, and Dadeng-Xiaodeng) during the wet seasons. Seasonal occurrence patterns may be associated with the seasonal prey shifts between these different environments.