Population differences in the pigmentation of Indo-Pacific humpback dolphins, Sousa chinensis, in Chinese waters

Spotting pigmentation was compared amongst three putative populations of Sousa chinensis: eastern Taiwan Strait (ETS; n=31), Pearl River Estuary ( PRE; n=188) and Jiulong River Estuary (JRE; n=10). Spotting intensity on dorsal fins and bodies of each dolphin was scored from 1 ( least spotted) to 4 ( most spotted) by nine independent subjects and the means of their scores were analysed using analysis of variances ( with post-hoc comparisons) and multiple t-tests. Dorsal fins of ETS dolphins were more spotted when compared to those of the PRE (p < 0.0001) and JRE (p < 0.0001), but those of PRE vs. JRE dolphins were not significantly different. Body spotting comparisons for all regions were not significantly different. The most noticeable character was the relative differences in spotting intensity between dorsal fins and bodies; dorsal fins were generally as, or more, spotted than bodies of ETS dolphins, while dorsal fins were generally less spotted than bodies of PRE and JRE dolphins. ETS dolphins also maintained spotting on their dorsal fins throughout all spotting phases of the body, whereas dorsal fins of PRE and JRE dolphins became unspotted well before their bodies. These results show that the ETS dolphins are distinct and apparently diagnosable from the PRE and JRE populations.