Indo-Pacific bottlenose dolphins Tursiops aduncus in Amakusa, western Kyushu, Japan

Abstract

A year-round resident population of bottlenose dolphins is known in the coastal waters of Amakusa-Shimoshima Island, western Kyushu (130 ∞ 07 ¢ E, 32 ∞ 33 ¢ N). 1 There are two types of bottlenose dolphins, the aduncus and the truncatus types, in the Indo-Pacific regions. 2–4 In Japanese waters, bottlenose dolphins with ventral spotting and small body size, which are characteristics of the aduncus type, 2–4 are reported from the Amami Islands (129 ∞ 22 ¢ E, 28 ∞ 18 ¢ N), 5,6 Kagoshima Bay (130 ∞ 37 ¢ E, 31 ∞ 30 ¢ N; Kishiro T. pers. comm., 2000), Mikura Island (139 ∞ 36 ¢ E, 33 ∞ 52 ¢ N) 7 and the Bonin Islands (142 ∞ 11 ¢ E, 26 ∞ 05 ¢ N). 8 Recent taxonomic re-examinations of bottlenose dolphins have indicated that the two types are separate species, Tursiops aduncus and T. truncatus . 9–13 The objective of the present paper is to identify the species of bottlenose dolphins off Amakusa. During our population studies of bottlenose dolphins in the coastal waters of Amakusa-Shimoshima Island, which were initiated in 1994, we were able to obtain samples and data from two carcasses. Both of the specimens were male; MIE001, taken incidentally by a gill net on 26 July 1995; and MIE003, stranded on a beach on 3 May 1998. The age of the two specimens was determined by reading the number of layers on decalcified and hematoxylin-stained tooth sections after Kasuya and Matsui. 14 We took a total of 34 cranial and postcranial measurements following Perrin. 15