The "Southern form" of short-finned pilot whale (Globicephala macrorhynchus) in tropical west Pacific Ocean off Taiwan

The short-finned pilot whale (Globicephala macrorhynchus) is a mid-sized toothed whale, widely distributed throughout warm-temperate to tropical regions of the Atlantic, Pacific, and Indian oceans. There is suggestive evidence that the taxonomy within the species is unresolved: a "Southern form" in southern Japanese waters is considered distinctive in its morphological, ecological, and genetic characteristics to a "Northern form" found in northern Japanese waters, and each might represent different subspecies or species. Short-finned pilot whales in the tropical west Pacific are poorly studied and their taxonomic status remains uncertain. The aim of this study was to determine the phenotype(s) and genotype(s) of pilot whales sighted or sampled from Taiwanese waters and compare them with whales found in adjacent Northeast and Southeast Asian waters. We examined 892 photographs taken from 14 groups of whales at sea around Taiwan, as well as the body length and photographic records of 19 whales stranded on the Taiwanese coast including genetic data (derived from a 689-bp mitochondrial DNA control region fragment) from eight of these. We also examined a group of short-finned pilot whales in a video clip filmed in the South China Sea, as well as a 593-bp mitochondrial DNA control region fragment sampled from two whales in Philippine waters. Our results revealed morphological and genetic similarities to available data from the more northerly located "Southern form" short-finned pilot whales from Japan, and indicate that the Southern form whales are indeed distributed more southward into the tropical west Pacific: viz, in the waters around Taiwan, in the South China Sea, and in the Philippines. The extent of the southern boundary for the range of the Southern form of short-finned pilot whales in the tropical west Pacific Ocean could be better defined with further observational and genetic studies.