Blackwell Science, LtdOxford, UK FISFisheries Science0919-92682003 Blackwell Science Asia Pty Ltd 693June 2003 669 Tursiops aduncus in Amakusa M Shirakihara et al. 10.1046/j.0919-9268.2003.00669.x Original Article654656BEES SGML
FISHERIES SCIENCE
2003; 69: 654–656
Short Paper
Indo-Pacific bottlenose dolphins Tursiops aduncus in Amakusa, western Kyushu, Japan Miki SHIRAKIHARA,1* Hideyoshi YOSHIDA2 AND Kunio SHIRAKIHARA3 Shinjyuku, Tokyo 162-0052, 2National Research Institute of Far Seas Fisheries, Shimizu, Shizuoka 424-8633 and 3Ocean Research Institute, University of Tokyo, Nakano, Tokyo 164-8639, Japan 1
KEY WORDS: Amakusa, mtDNA cytochrome b gene sequences, skull measurements, Tursiops aduncus. 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 Total DNA extracted from the skin was used to sequence 369 base pairs of the mtDNA cytochrome b gene following the methods of Yoshida and Kato.16 *Corresponding author: Tel: 81-3-3232-3842. Fax: 81-3-3232-3842. Email:
[email protected] Received 3 July 2001. Accepted 16 November 2001.
Body length and age were 181 cm and 1 year for MIE001 and 251 cm and 12 years for MIE003. These body lengths were below the mean growth curve of T. truncatus off northern Kyushu (i.e. 190.4 cm at 0.5 years and 295.0 cm at 11.5 years),7 but were similar to those reported for T. aduncus in other waters.3,4,11,13 Most of the skull measurements of MIE003 were within the range of T. aduncus off South Africa4 but were outside of the corresponding range of T. truncatus in the same region (Table 1). Ross found significant differences in measurements of the rostral and premaxillary widths (no. 3–6 in Table 1) between two species in South Africa.4 The rostral width in the proximal half of its length for T. aduncus was narrower than that for T. truncatus. This feature was also clearly evident in our specimen MIE003 (Fig. 1a,b). In lateral view, the premaxillary convexity at a length of approximately two-thirds distance from the tip was clear for MIE003 (Fig. 1c), which was one of the characteristics of the skull of T. aduncus in South Africa and China.4,12 The ratio of greatest width of external nares to greatest parietal width is a key distinguishing feature between T. aduncus (≥0.313) and T. truncatus (£0.306) in Chinese waters.12 The ratio of 0.356 for MIE003 was within the former range. Ross suggested that tooth diameter of T. aduncus would be smaller than that of T. truncatus.4 The difference was also reported for coastal and offshore bottlenose dolphins in the eastern North Pacific.17 Maximum tooth diameter measured on tooth section of MIE003 was 7.2 mm, which was lower than the mean diameter of female T. truncatus off northern Kyushu.7 Total vertebrae counts are 59–62 for T. aduncus and 64–67 for T. truncatus.4,12 One or two caudal
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Table 1 Skull measurements (mm) of the Indo-Pacific bottlenose dolphins Tursiops aduncus off Amakusa (MIE003) No.†
Measurements
1 2 3 4 5 6
Condylobasal length Length of rostrum Width of rostrum at base Width of rostrum at 60mm Width of rostrum at midlength Width of premaxillaries at midlength of rostrum Width of rostrum at 3/4 length Distance from tip of rostrum to external nares Distance from tip of rostrum to internal nares Greatest preorbital width Greatest postorbital width Least supraorbital width Greatest width of external nares Greatest width across zygomatic processes of squamosal Greatest width of premaxillaries Greatest parietal width Greatest length of left posttemporal fossa Greatest width of left posttemporal fossa Length of left orbit Length of antorbital process of left lacrimal Greatest width of internal nares Greatest length of left pterygoid Length of upper left tooth raw No. teeth-upper left No. teeth-upper right No. teeth-lower left No. teeth-lower right Length of lower left tooth row Greatest length of left ramus Greatest height of left ramus Length of left mandibular fossa
7 8 9 10 11 12 13 14 15 16 19 20 25 26 27 28 32 33 34 35 36 37 38 39 40
499‡ 295 (59.1) 119 (23.8) 87 (17.4) 71 (14.2) 41 ( 8.2) 57 (11.4) 335 (67.1) 325 (65.1) 216 (43.3) 241 (48.3) 210 (42.1) 57 (11.4) 245 (49.1) 88 (17.6) 160 (32.1) 110 (22.0) 72 (14.4) 63 (12.6) 41 ( 8.2) 64 (12.8) 72 (14.4) 246 (49.3) 26 25 26 25 250 (50.1) 426 (85.4) 88 (17.6) 144 (28.9)
†
Follows Perrin.15 Tip of rostrum was slightly broken. In parentheses, percentage of condylobasal length. ‡
vertebrae were probably missing from the postcranial skeleton of MIE001. This led to an estimated total vertebral count of 59–60, which is within the range of T. aduncus. We compared the mtDNA cytochrome b gene sequences of Amakusa specimens with published sequences of two T. aduncus (GenBank accession numbers: AF084091 and AF084092) and three T. truncatus (AF084093–AF084095)9 using the program CLUSTAL W 1.7.18 The number of nucleotide substitutions between them ranged from 0 to 14. All substitutions were transitional changes and no
Fig. 1 Skull of a male Tursiops aduncus (MIE003) stranded on a beach of Amakusa-Shimoshima Island: (a) dorsal view; (b) ventral view; and (c) lateral view.
inserts or deletions were observed. MIE003 and an Indonesian specimen of T. aduncus shared an identical sequence. The number of nucleotide substitutions among the present specimens and the aforementioned T. aduncus ranged from 0 to 5, which was similar to numbers observed among T. truncatus (1–4). However, the values were greater if compared between two species (9–14). A phylogenetic tree was generated using the neighborjoining method19 with the program CLUSTAL W 1.718 (Fig. 2). Amakusa specimens were located within a clade containing cited T. aduncus (bootstrap value: 86%). Tursiops truncatus formed a distinct clade (98%). All the results identified the two specimens as T. aduncus. Bottlenose dolphins commonly form a large group of approximately 100 individuals in the coastal waters of Amakusa. Dolphins with ventral spotting were frequently found in the group (Fig. 3). We concluded that there is a resident population of T. aduncus in the coastal waters of Amakusa-Shimoshima Island.
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4.
Fig. 2 Phylogenetic relationships of cytochrome b gene sequences from Amakusa specimens (MIE001 and 003), Tursiops aduncus and T. truncatus. Globicephala melas added as outgroup. The distance scale indicates the percentage divergence between each pair of sequences. Numbers represent bootstrap percentages from 1000 iterations. Sequences of MIE001 and MIE003 have been deposited in GenBank Sequence Database under accession numbers AF425253 and AF425254, respectively.
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Fig. 3 Ventral spotting of Tursiops Amakusa-Shimoshima Island.
aduncus
off
We are grateful to S Nojima, S Arakaki, University of Kyushu; and S Kiguchi for providing information of Amakusa specimens. We would like to thank M Amano, University of Tokyo; T Otake, M Yoshioka, Mie University; and S Hasegawa, T Oike, Minami Chita Beach Land for their suggestions and courtesy. The manuscript was improved by useful comments from T Kasuya, Teikyo University of Science and Technology and William A Walker, National Marine Mammal Laboratory, NOAA, USA.
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