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

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. 在大多数分布区内，中华白海豚的色素沉着模式尚未得到很好的研究。本研究应用两种方法：前人应用的主观评分法和新开发的数字化评分法，来评估厦门、南流江-大风江河口（DRE），和沙田-草潭（SC）群体中137头中华白海豚个体的斑点密度。两种评分方法均表明， 3个群的中华白海豚背鳍的斑点密度低于身体的斑点强度。SC和DRE中华白海豚的背鳍斑点强度、身体斑点强度，和背鳍和身体上的斑点差值，均显著高于厦门中华白海豚，而SC和DRE之间没有显著差异。色素沉着与年龄相关，我们的研究表明年轻和成年个体呈现出与上述相似的结果。本文结合前人的研究，阐明了中国水域内中华白海豚色素沉着的普遍规律：东台湾海峡和珠江河口的种群分别代表了两种极端的色素沉着模式，而厦门种群，北部湾种群（包括SC社群和DRE社群）代表中间形式，这些群体是统计学显著不同的存在类型。 [ABSTRACT FROM AUTHOR]