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Cetaceans in the Indian Ocean Sanctuary: A Review

Cetaceans in the Indian Ocean Sanctuary: A Review

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species distributed over the continental shelf (Peddemors, 1999). The fourteen species are made up of two forms of Tursiops, Sousa chinensis, Delphinus delphis, Stenella attenuata, S. longirostris, Lagenodelphis hosei, Grampus griseus, Steno bredanensis, Globicephala melas, G. macrorhynchus, Peonocephala electra, Orcinus orca and Pseudorca crassidens. At a recent conservation assessment and management plan (CAMP) workshop for South African mammals, forty-five cetaceans were assessed, including 1 Physeteridae, 2 Kogidae, 9 Ziphiidae, 20 Delphinidae, 1 Balaenidae, 1 Neobalaenidae, 8 Balaenopteridae (Peddemors, et al., 2002). Only one of the species assessed does not occur within the IOS, Cephalorhynchus heavisidii. It is now recognised that there are probably two ecotypes of Tursiops truncatus within the southern African IOS region divided into 3 populations: two inshore (the smaller east coast form designated as T.aduncus) and one offshore (Ross, 1984; Ross and Cockcroft, 1990). The east coast form is found primarily within the 50- m isobath (Ross et al., 1987) from Mozambique to False Bay in the southwest. The offshore Tursiops is of the inshore west coast form and Findlay et al. (1992) suggests that there may be a contiguous population from east to west coasts. At least 25 species of cetaceans are known to occur in the Eastern African Region, including six baleen whales, 10 toothed whales and nine dolphins (de Lestang, 1993; La Hausse de la Louviere, 1991). The small cetaceans which are commonly found in coastal and inshore waters throughout the eastern region are S. chinensis and Tursiops truncatus, and spotted, striped and spinner dolphins (Stenella sp.) are also reported from throughout the region (Gambell et al., 1975; Small and Small, 1991). Spotted and spinner dolphins are found in both coastal and open oceanic waters, while the striped dolphin seems to be comparatively more pelagic in this eastern region (Borobia, 1997). Sightings & strandings South Africa Land-based and aerial surveys and ship-based transects have been conducted during the last decade (e.g. Cockcroft, Ross and Peddemors, 1990, 1991; Cockcroft, Ross, Peddemors and Borchers, 1992; Peddemors, 1993; Findlay et al., 1994; Findlay and Best, 1996a & b: Best 1996, Ljungblad et al., 1997; Ersts and Rosenbaum, submitted) along with a series of studies on freeranging delphinids throughout the region (e.g. Peddemors, 1995; Karczmarski, 1996; Karczmarski and Cockcroft, 1997, 1999; Keith et al., in press) and renewed investigations into feeding biology (e.g. Barros and Cockcroft, 1991; Cockcroft and Ross, 1990; Cockcroft, Haschik and Klages, 1993; Sekiguchi et al., 1992; Young and Cockcroft, 1994; Plön et al., 1997). Several investigations into the life history of South African cetaceans have also been completed using stranded and by-caught animals (e.g. Mendolia, 1990; Kroese, 1993; Plön et al., 1997, 1998). Mozambique Data on delphinid distribution and abundance are scant for Mozambique. However, in the waters of Mozambique and southern Madagascar, a minimum of 11 species have been reported by Peddemors et al. (1997b) including Tursiops truncatus; Grampus griseus, Globicephala macrorhynchus, Stenella attanuata, S. longirostris, S. coeruleoalba, Peponocephala electra, Pseudorca crassidens, Sousa chinensis, Delphinus delphis and Steno bredanensis. Tursiops truncatus and Sousa chinensis are known to inhabit both Maputo (25°35’S-26°15’S and 32°35’E-33°00’E) and Bazaruto Bays (21°30’S-22°S, Cockcroft and Krohn, 1994). Recent cetacean research efforts here have focussed on determining humpback whale (Megaptera novaeangliae) distribution and abundance in the south-west Indian Ocean (Best et al., 1996a&b; Findlay et al., 1994). Madagascar Distribution and abundance studies of humpback whales in northeastern Madagascar (Rosenbaum et al. 1997; Ersts and Rosenbaum, submitted) and southern Madagascar have been conducted (Best et al., 1996; Rosenbaum, in press). Razafindrakoto et al. (2001) reported on humpback whale song from Antongil Bay. An overview of marine mammals of Madagascar is presented in Rosenbaum (in press) and cetacean surveys in Madagascar have also been reported by Cockcroft and Young (1998) and Peddemors et al. (1999). A note on recent southern right whale (Eubalaena australis) sightings in Madagascar is provided by Rosenbaum et al. (2001a). An overview of what is known about Sousa chinensis species is provided in Baldwin et al. (2002). 5

Data collected between 1995 and 2001 confirmed that 4 large whale species occur in Madagascar’s waters and 4 other species are suspected to occur there. Numerous species of small cetaceans including oceanic dolphins, several species of “blackfish” and pygmy sperm whales have also been documented (Rosenbaum, in press). Mauritius Corbett (1994) reported on the results of a yearlong study in the Mascarenes, with an emphasis on the Island of Mauritius. Sperm whales and spinner dolphins were the most abundant species, but fin whales (Balaenoptera physalus), blue whales (B. musculus), humpback whales and several odontocetes species (spotted dolphins, Risso’s dolphins, striped dolphins, bottlenose dolphins, short-finned pilot whales (Globicephala macrorhynchus), melon-headed (Peponocephala electra) or pygmy killer whales (Feresa attenuata) and two species of beaked whales were also recorded. Corbett (1994) also suggested that sperm whales use the area yearround. In addition, Blainville’s beaked whales (Mesoplodon densirostris) have been found stranded on Mauritius (Michel and van Bree, 1976). Tanzania The occurance and abundance of marine mammal species in Tanzanian waters is poorly known and no dedicated studies have been conducted to date (Stensland et al., 1998). Only a few publications exist reporting sightings, strandings and museum specimens (de Lestang, 1993). However, several species of dolphins have been reported in the waters surrounding Zanzibar Island. In Menai Bay, Indo-Pacific humpback dolphins (S. chinensis) and bottlenose dolphins (Tursiop sp.) have been reported (see Stensland et al., 1998). In the north, bottlenose dolphins and spinner dolphins (S. longirostris) have been observed (Ortland, 1997). Another dolphin species that has been reported is the rough-toothed dolphin (Steno bredanensis) (Chande et al., 1994, unpubl report to UNEP). Dolphins (without reference to species) have also been reported in the Rufiji Delta, Sadani, around Latham Island, Tanga (north Tanzania) and Mtwara (south Tanzania) (Lindén and Lundin, 1996). Humpback whales (Megaptera novaeangliae) are known to migrate along the coast of Zanzibar Island (Ortland, 1997). Kenya Sightings of small groups of cetaceans and cetacean strandings are recorded for Kenya (KWS, 1996). The larger whale species known or believed to occur in Kenyan waters are Physeter macrocephalus, Orcinus orca, Megaptera novaeangliae, Balaenoptera edeni, B. acutorostrata and Peponocephala electra. Five species of dolphins were positively identified during an aerial survey in 1994, including Tursiops sp., Delphinus sp., Sousa chinensis, Stenella longirostris, S. attenuata. Additionally, Lagenodelphis hosei, Grampus griseus and S. coeruleoalba are also thought to occur in Kenyan waters (Wamukoya et al., 1996). Somalia and Seychelles Small and Small (1991) reported on cetacean observations from Somalia during boat based surveys conducted from September 1985 until March 1987. 14 different species were reported: Blue whale, Bryde’s whale (B. edeni), sperm whale, melon-headed whale, false killer whale (Pseudorca crassidens), killer whale, shortfinned pilot whale, Indo-Pacific humpback dolphin, common dolphin, Tursiops sp., Risso’s dolphin, spotted dolphin, spinner dolphin and striped dolphin. Ballance and Pitman (1998) conducted a cetacean survey of the Western Tropical Indian Ocean (WTIO) and compared their findings with the cetacean communities of two other tropical ecosystems. They found that the WTIO was similar to the eastern tropical Pacific (ETP) and the Gulf of Mexico (GM) in several respects: Firstly, the same species were common and or rare, regardless of ocean. Second, these differences in abundance were due primarily to differences in encounter rate, and less to school size. Third, regardless of ocean, three species comprised the majority of the cetaceans encountered, Stenella attenuata, S. longirostris, and S. coeruleoalba. However, the ranking of abundance for these three species differed between oceans: S. attenuata appeared to be abundant in the ETP and GM but much less common in the WITO (Ballance and Pitman, 1998). Although habitat preferences for S. attenuata appeared to overlap considerably with those of S. longirostris in the ETP, there may actually be significant differences between these two species (Ballance and Pitman, 1998). Distribution and migratory patterns Using sightings of photo-identified individuals, Best et al. (1993) reported on long-range 6

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