From August 2010 to July 2015,monthly field surveys were conducted to explore the habitat fidelity,seasonal group characteristics and occurrence pattern of Indo-pacific humpback dolphin(Sousa chinensis)in Xiamen and adjacent waters,Fujian Province,China.The photographic analyses indicate that majority of the identified humpback dolphins showing interannual habitat fidelity throughout the study period.The average group sizes varied significantly among four seasons(F =14.168,df =3,P < 0.001),humpback dolphins formed larger groups in dry seasons(winter and spring)than in wet seasons(summer and autumn)(U =2117.50,P < 0.001).The sighting encounter rate also varied significantly among four seasons(F =7.612,df =3,P < 0.001),while individual encounter rate was not significantly different among four seasons(F =0.494,df =3,P =0.688).Humpback dolphins,as well as the foraging events,mainly occurred in inner harbors(Western Harbor and Tongan Bay)during dry seasons,and mainly occurred in the peripheral areas(Jiulong River Estuary,Wuyu,and Dadeng-Xiaodeng)during wet seasons.The seasonal occurrence pattern of humpback dolphins might be consistent with the seasonal shifts of preys between the inner harbors and peripheral waters.Groups containing newborn calves were mostly found in Jiulong River Estuary and Dadeng-Xiaodeng waters,indicating these two regions were also important for calving,and therefore should be given high priority for conservation.