Synopsis:  I completed my Master degree at National Taiwan University (NTU) under a joint supervision of Prof. L-S Chou (NTU) and Dr. Leszek Karczmarski (HKU). My research project investigated the population structure, social behaviour and reproductive dynamics of Indo-Pacific humpback dolphins (Sousa chinensis) off the west coast of Taiwan, a small population numbering less than 100 individuals and listed under the IUCN criteria as Critically Endangered.  In my study, I used photo-identification mark-recapture techniques to study the behavioral and reproductive dynamics and, during a 4-year study period (2007-2010) with 352 boat-based surveys and over 60,000 photographs, I photo-catalogued 98 individuals, of which 22 were reproductively active females and 27 were calves. Hierarchical cluster analysis and multidimensional scaling revealed that the population consists of two communities, each with a moderately fluid pattern of geographic and social fidelity. Although the communities are not entirely discrete, their interactions are limited to "casual acquaintances” while modeled lagged identification rates suggest that “emigration and reimmigration” best describes their movement and ranging pattern. Although some individuals can be seen in both communities, their heterogeneous movement pattern indicates that over a longer time scale they prefer a certain region which is their respective community range. The degree of separation between the two communities requires further investigation, but it seems to correspond with features of local habitat; and it is possible that historically the separation is a relatively recent event related to anthropogenic impacts, as there is an area of increased industrial activity located approximately in the middle between the two communities which might act as a human-caused barrier. The dolphins give birth throughout the year, but with a peak in spring and summer.  A suite of estimated population parameters indicates slow population growth rates, which further highlights the vulnerability and sensitive conservation status of this dolphin species in Taiwanese waters, underscoring the notion that an informed conservation management plan is urgently needed.