Geographic variation in pigmentation patterns of Indo-Pacific humpback dolphins (Sousa chinensis) in Chinese waters

Abstract

The pigmentation patterns of Indo-Pacific humpback dolphins have not been well studied throughout most of the species' range. In the present study, both the subjective scoring method and a newly developed quantified scoring method were employed to evaluate the spotting intensity of 137 humpback dolphin individuals from the Xiamen and Beibu Gulf putative populations, including the Dafengjiang-Nanliujiang River Estuary (DRE) and Shatian-Caotan (SC) communities. Both scoring methods indicated that spotting intensity on the dorsal fin was lower than that on the body of humpback dolphins in all 3 groups. The SC and DRE humpback dolphins had significantly greater dorsal fin, body spotting intensity, and greater differences between spotting on the dorsal fin and body than Xiamen dolphins, while no differences were found between SC and DRE. The pigmentation variation is related to age class, young dolphins have more spotting density than adults, and young and adults showed similar geographical variation as above. The present paper, in combination with previous research, clarifies the general pattern of pigmentation for Chinese humpback dolphins. Eastern Taiwan Strait and Pearl River Estuary populations represent 2 extreme patterns of pigmentation, while the Xiamen population, SC community, and DRE community seem to be intermediate. The results suggest that these groups should be viewed as demographically distinct forms.