Differences in the external morphology of two sympatric species of bottlenose dolphins (genus Tursiops) in the waters of China

Abstract

Clear genetic and osteological characters exist to distinguish 2 sympatric species of bottlenose dolphins (genus Tursiops) in the waters of China. However, these characters are not useful for the identification of free-ranging dolphins. To determine if these species could be differentiated by external morphology, a discriminant analysis was performed on 8 external morphometric characters of 57 specimens, 40 of which were classified a priori as T. truncatus and 17 as T. aduncus using genetic, osteological, and other information. External morphological separation of the 2 species was highly significant. Furthermore, discriminant scores were nonoverlapping, and classification functions were successful in classifying several new specimens from the waters of China and Indonesia. Rostrum length as an absolute measure and as a proportion of total body length or snout-to-eye length revealed nonoverlapping distributions for the 2 species in the waters of China and thus offered useful field characters for classifying fresh carcasses, stranded individuals, captive specimens, photographs, and in some cases free-ranging individuals.