Social structure and reproductive parameters of Indo-Pacific humpback dolphins (Sousa chinensis) off the west coast of Taiwan
Date Issued
2011
Date
2011
Author(s)
Chang, Wei-Lung
Abstract
Indo-Pacific humpback dolphin (Sousa chinensis) population that inhabits west coastal waters of Taiwan was estimated to number less than 100 individuals and is listed under the IUCN criteria as “Critically Endangered”. In this study, photo-identification mark-recapture techniques were applied to investigate their behavioral and reproductive dynamics. During a 4-year study period (2007-2010), 352 boat-based surveys were performed, resulting with over 60,000 photographs; 98 individuals were photo-catalogued, 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. There seems to be further differences between individuals from both communities, including different percentage of coloration/age-stages and the number of mature females. 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. It is also possible that the separation is a historically more 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 social behaviour might be performed as mate-searching behaviour, while the parturition happened throughout the year with a peak in spring and summer, resulted a crude birth rate of 0.064 ± s.d. 0.037. The mean survivorship and survival rate to Age 1 were estimated at 0.66 ± s.d. 0.20 and 0.78 ± s.d. 0.39, respectively; and the recruitment rate (at Age 1) was 0.090 ± s.d. 0.030 with calving interval approximating 3.52 ± s.d. 0.28 years with the weaning age at around 3-4 years old. Estimated suite of population parameters indicating a slow population growth rates highlight further the vulnerability and sensitive conservation status of Indo-Pacific humpback dolphins off Taiwan; indicating that informed conservation management plan is urgently needed.
Subjects
Taiwan
Sousa chinensis
photo-identification
community structure
group dynamics
site fidelity reproductive parameters
SDGs
Type
thesis
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