Aquatic Mammals 2004, 30(1), 111-124, DOI 10.1578/AM.30.1.2004.111 The Indo-Pacific Humpback Dolphin of the Arabian Region: A Status Review Robert M. Baldwin,1 Moth Collins,1 Koen Van Waerebeek,2 and Gianna Minton1 1Oman Whale and Dolphin Research Group, P.O. Box 2531, CPO 111, Sultanate of Oman 2Peruvian Centre for Cetacean Research (CEPEC), Museo de los Delfines, Pucusana, Peru Abstract relative values found in individuals from the Saudi Arabian Gulf coast. Cranial abnormalities were Records of Indo-Pacific humpback dolphin sight- few. Recommendations are made for conserva- ings, strandings, and museum specimens in the tion management-oriented research focusing on Arabian region were compiled and used to review stock identity and status assessments, as well as the distribution and status of this species. Nominal for monitoring of fisheries by-catch, clearer defi- usage of Sousa chinensis (Osbeck, 1765) has been nition of other threats, continued specimen and retained as a pragmatic measure, although the sample collection, and training of local scientists. species present in the region resembles Sousa plumbea (Cuvier, 1828). Little is known about Key Words: Humpback dolphin, Sousa, Arabia, the ecology of this species in the region. Most Persian Gulf, Middle East, Oman, distribution, available information on S. chinensis in the region abundancy conservation originates from the Sultanate of Oman, where this species is among the most commonly recorded Introduction cetaceans; however, there is no absolute measure of abundance for anywhere in the region and the Available information on general and specific status of the species is unknown. Distribution aspects of small cetaceans of the Arabian region, is described for the region to include much of including S. chinensis, can be found in reviews the Arabian (Persian) Gulf, Arabian Sea, Gulf by Leatherwood (1986), de Silva (1987), and of Aden, and Red Sea, but notably excludes the Baldwin et al. (1999) and in results of surveys Gulf of Oman. This discontinuous distribution (Baldwin, 1995; Beadon, 1991; Frazier et al., suggests the possible presence of discrete popu- 1987; Gallagher, 1991; Papastavrou & Salm, lations within the region. Beach-cast/dead indi- 1991; Preen, 1987; Small & Small, 1991). viduals represent nearly two-thirds of all records Research and observations of cetaceans in the (n=303) of this species in Oman. Live sightings region have focused on defined areas, with most indicate unusually large group sizes (up to 100 available information on humpback dolphins individuals) in the Arabian Sea and Arabian Gulf. coming from waters off the Sultanate of Oman Occasional associations with Tursiops sp. and and the southern shores of the Arabian Gulf, Delphinus capensis tropicalis were documented. particularly the United Arab Emirates (UAE) and Mating behavior and the presence of calves Saudi Arabia. In the Arabian region, S. chinen- were recorded in the months of April and May, sis was first identified from a skull collected in and calves were also reported in June, October, March 1948 from Karaman Island, Red Sea, by D. November, and December. Threats to humpback Thompson. The specimen is curated at the Natural dolphins in the Arabian region include incidental History Museum in London (BM 1948.3.13.1) capture in fishing nets, coastal and offshore devel- (Leatherwood, 1986). Subsequent records came opment (e.g., land reclamation, dredging, port and from both the western (Al Robbae, 1970, 1974) harbor construction), pollution, boat traffic, oil and the eastern (Pilleri & Gihr, 1974) Arabian and gas exploration (including seismic survey- Gulf. Evidence that additional early work was in ing), military exercises, and biotoxins associated progress in the region is provided by Gallagher with red tide events. Evidence for historic and (1991), who documented collections of humpback current directed catches of S. chinensis is limited, dolphins from Bahrain, United Arab Emirates but opportunistic hunting may occur. Intraspecific (UAE), and Oman that date back to the 1970s. variation in cranial measurements of individuals Surveys conducted specifically to observe and from the Arabian Sea coast of Oman fall within record cetaceans in the region began in 1973 © 2004 EAAM 112 Baldwin et al. (Pilleri, 1973). Several surveys were conducted Materials and Methods in the region during the early 1980s (Alling et al., 1982; Harwood, 1981; Keller et al., 1982; Review of Available Literature and Databases Robineau & Rose, 1984). These included a Data reviewed here come from published litera- survey of humpback dolphins in the UAE in 1984 ture, and from databases of cetacean records for (UAECD) and surveys conducted for dugongs both the United Arab Emirates (UAE) and Oman, (Dugong dugon) in the Arabian Gulf (1986 and held by the Emirates Natural History Group, Abu 1999) and Red Sea (1986), which included docu- Dhabi, and the Oman Natural History Museum mentation of sightings of humpback dolphins (ONHM), respectively. These are referred to in this (Preen, 1989, in press a). Results of the latter paper as the UAE Cetacean Database (UAECD) survey prompted an investigation of extensive and the Oman Cetacean Database (OMCD). The marine mammal mortality in the Arabian Gulf latter is current and comprehensive, whereas the (Preen, in press b; ROPME, 1986). Other survey former was discontinued in 1995. These databases work in the Arabian Gulf focused specifically on were established and maintained by one or more small cetaceans, including S. chinensis (Baldwin, of the authors and incorporate records from a vari- 1995, 1996; Robineau & Fiquet, 1994, 1996). ety of sources, including published literature, data Recent data on humpback dolphins of the collected by the authors during systematic surveys region come from incidental observations at sea and along shorelines, data collected during recorded during more general surveys of marine other dedicated cetacean surveys, data from addi- and coastal habitats, particularly along the coast tional specimens curated at the ONHM and in of Oman (Papastavrou & Salm, 1991; Salm, private collections in the UAE, and some inciden- Jensen, & Papastavrou, 1993; Weidleplan, 1992), tal data submitted by other recorders. All unpub- as well as in Somalia (e.g., Schleyer & Baldwin, lished records referred to in the present account 1999; Small & Small, 1991). Cetacean research were either made by the authors or verified to have in Oman undertaken by the authors included sufficient and reliable supporting data to enable systematic small boat surveys in nearshore and discussion. Unconfirmed records or those lacking offshore waters, as well as surveys for beach-cast supporting information have been discounted and cetaceans. are not included. Because records from published The taxonomy of the genus Sousa remains sources also are stored in the databases, analysis unresolved. A wide variety of species’ definitions of information included the sorting of data to have been suggested in the past few decades, from ensure that no duplication of records occurred. a single highly variable species, S. chinensis, to recognition of all five nominal species (see discus- Study Area sion by Rice, 1998). As a pragmatic measure, and We define the Arabian region as coastal and off- until morphological and molecular genetic studies shore waters of the Arabian Peninsula, including more firmly establish taxonomic relationships waters of the Arabian Gulf, Gulf of Oman, west- and nomenclature, we temporarily retain nominal ern Arabian Sea, Gulf of Aden, and Red Sea. Data usage of S. chinensis (Osbeck, 1765). Populations from elsewhere, such as along the African coast of in the Arabian region show morphological affili- the Red Sea, are included in cases where these are ation to S. plumbea (Cuvier, 1829), however—a considered relevant or appropriate. species recognized by Hershkovitz (1966) and followed by Rice (1998) for animals that inhabit Museum Specimens waters from the western Bay of Bengal, the To describe intraspecific cranial variation, 38 Arabian Sea, and south to South Africa. Fairly cranial measurements and tooth counts (Table 1), translated in English as “plumbeous dolphin,” S. slightly modified from Perrin (1975), were taken plumbea aptly describes the widely recognized for 28 skulls collected from the coasts of Oman colouration distinction from the lightly coloured (Table 2). The sample was not gender-stratified, as Pacific humpback dolphin or Chinese white skulls were derived exclusively from beach-cast dolphin S. chinensis. The plumbeous dolphin specimens, many of which were too decomposed also exhibits a highly conspicuous dorsal hump to allow for sex determination. Cranial maturity that is absent in S. chinensis (see Jefferson & was determined from the degree of fusion in seven Karczmarski, 2001), while its cranial characteris- indicative cranial suture lines (Van Waerebeek, tics indicate taxonomic differentiation at least at 1993), while taking into account possible sec- the subspecific level (Jefferson & Van Waerebeek, ondary suture de-fusing in highly weathered 2004). specimens. Indo-Pacific Humpback Dolphins in the Arabian Region 113 Table 1. Cranial measurements and tooth counts used for in the Musandam region of Oman (Baldwin & descriptive craniometrics of Sousa from Oman; slightly Salm, 1994; Pilleri & Gihr, 1974), and off Iran modified from Perrin (1975). (Pilleri & Gihr, 1974). This species’ distribution (Figures 2 & 3) 1. Condylobasal length (cbl) extends into the coastal waters of the northern 2. Rostrum length (rl) extreme of the Gulf of Oman as far south as 3. Rostrum width at base (rwb) 26°07’N, 56°23’E in Musandam. No sightings 4. Rostrum width at 60mm (rw60) 1 or strandings of S. chinensis have been reported 5. Rostrum width at ⁄4 length (rw14l) between Musandam and Ra’s Al Hadd (22 30’N, 1 ° 6. Rostrum width at ⁄2 length (rw12l) 59 49’E), which marks the boundary between 3 ° 7. Rostrum width at ⁄4 length (rw34l) the Gulf of Oman and the Arabian Sea (Baldwin 1 8. Premaxillary width at ⁄2 length (prmx12l) & Salm, 1994; Salm et al., 1993). The range of 9. Tip of rostrum to right external nare (trextn) S.