Madagascar Ridge IMMA

Size in Square Kilometres

412,817 km2

Qualifying Species and Criteria

Sperm whale – Physeter macrocephalus

Criterion A; B(2)

Pygmy blue whale – Balaenoptera musculus brevicauda

Criterion A; B(2); C(2); C(3)

Antarctic blue whaleBalaenoptera musculus intermedia

Criterion A

Bryde’s whaleBalaenoptera edeni

Criterion C(2)

Humpback whale – Megaptera novaeangliae

Criterion C(3)

Sei whale – Balaenoptera borealis

Criterion A

Marine Mammal Diversity

Criterion D(2)

Eubalaena australis, Balaenoptera bonaerensis, Pseudorca crassidens, Caperea marginata, Berardius arnouxii, Ziphius cavirostris, Hyperoodon planifrons, Mesoplodon grayi, Mesoplodon layardii, Orcinus orca, Delphinus delphis, Stenella attenuata, Stenella coeruleoalba, Tursiops truncatus, Grampus griseus, Lagenodelphis hosei, Steno bredanensis



The Madagascar Ridge IMMA extends south from the southern coast of Madagascar into the wider Plateau of Madagascar and off the continental shelf. This IMMA is an important area for feeding pygmy blue whales (B. m. brevicauda), Bryde’s whales (Balaenoptera edeni brydei), sperm whales,  and potentially for other large whale species (i.e., fin whales, sei whales). Critically Endangered Antarctic blue whales (B. m. intermedia) were also recorded in the region. The Madagascar Ridge is also an important migratory corridor for migrating humpback whales (M. novaeangliae), southern right whales (E. australis) and potentially other species of large whales, including male sperm whales and other baleen whales. At least 23 species of cetaceans are known to occur in this region, including 9 species of baleen whales and 14 species of toothed cetaceans.

Description of Qualifying Criteria

Criterion A – Species or Population Vulnerability

The Madagascar Ridge area is an area used by pygmy blue whales (B. m. brevicauda) for feeding during the austral summer (Kasuya and Wada 1991, Best et al. 2003, Branch et al. 2007), sperm whales (Physeter macrocephalus) and a migratory corridor for southern right whales and humpback whales (Best 2007, Fossette et al. 2014). Surveys conducted in the region by Gambell et al. (1975) suggest that sperm whale is the most abundant large cetacean in the Madagascar Ridge area.

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

This region is an important habitat for blue whales, based on catch and sighting data (Branch et al. 2007), primarily pygmy blue whales. The sperm whale is the most abundant large cetacean species in the Madagascar Ridge area (Gambell et al. 1975). This region may have the highest densities of sperm whales in the southwestern Indian Ocean (Gambell et al. 1975). A compilation of available sighting records of blue and sperm whales throughout the western Indian Ocean (1972-2017) suggest that the Madagascar Ridge is one of the most critical habitats for these two species in the region (Tetley, Kiszka and Hoyt, unpublished data, Figure 3).

Criterion C: Key Life Cycle Activities

Sub-criterion C2: Feeding Areas

The Madagascar Ridge area is important for feeding pygmy blue whales (B. m. brevicauda) during the austral summer (Kasuya and Wada 1991, Best et al. 2003, Branch et al. 2007). Best et al. 2003 estimated blue whale abundance as 424-472 in December 1996 from the southwest tip of Madagascar and along the Madagascar Ridge.  Under a scientific research permit, Japanese whalers took large numbers of Bryde’s whales (>100) in the vicinity of the Madagascar ridge during 1976-1979, with detailed description of stomach contents indicating feeding (Kawamura 1980, Ohsumi 1980). These whales were described as Balaenoptera edeni brydei, which is distinct from coastal South African and southeastern Atlantic populations (Best 2001).  It could be used as a foraging ground for a large number of other species, but we currently do not have supporting evidence.

Sub-criterion C3: Migration Routes

The region is a migratory corridor for humpback whales (Best et al. 1998, Fossette et al. 2014, Cerchio et al. 2016) and southern right whales (Best 2007). The southern Madagascar shelf is important breeding habitat for Megaptera novaeangliae, as satellite telemetry data indicated extensive use of this habitat during the height of the breeding season (Cerchio et al. 2016; Trudelle et al. 2016; Dulau et al. 2017). Blue whales, male sperm whales and other species of baleen whales such as fin, Bryde’s and Antarctic minke whales also use this region as a migratory corridor (Gambell et al. 1975, Kasuya and Wada 1991, Best 2007).  Kasuya and Wada (1996) report B. physalus sightings immediately south of Madagascar (25°-30°S, 45°-55°E) during December, likely on southern migration, but well south of 30°S from January to April in presumed feeding habitat.

Criterion D: Special Attributes

Sub-criterion D2: Diversity

A total of 23 species of cetaceans have been recorded in the Madagascar Ridge area, including 9 species of baleen whales and 14 species of toothed cetaceans (Cerchio et al 2022).  These include Humpback whale (Megaptera novaengliae), Southern right whale (Eubalaena australis), Antarctic minke whale (Balaenoptera bonaerensis), Pygmy right whale (Caperea marginata), Cuvier’s beaked whale (Ziphius cavirostris), Arnoux’s beaked whale (Berardius arnouxii), Gray’s beaked whale (Mesoplodon grayi), Strap-toothed whale (Mesoplodon layardii), Killer whale (Orcinus orca), False killer whale (Pseudorca crassidens), Common dolphin (Delphinus delphis), Pantropical spotted dolphin (Stenella attenuata), Rough-toothed dolphin (Steno bredanensis), Striped dolphin (Stenella coeruleoalba), Risso’s dolphin (Grampus griseus), Common bottlenose dolphin (Tursiops truncatus), Fraser’s dolphin (Lagenodelphis hosei), Pygmy killer whale (Feresa attenuata) (Best et al. 1998, Fossette et al. 2014, Cerchio et al. 2016, Gambell et al. 1975, Kasuya and Wada 1991).

Supporting Information

Best, P.B. 2001. Distribution and population separation of Bryde’s whale Balaenoptera edeni off southern Africa. Mar. Ecol. Prog. Series 220: 277–289

Best, P.B. 2007. Whales and dolphins of the southern African subregion. Cambridge University Press, 338pp.

Best, P.B., Rademeyer, R.A., Burton, C., Ljungblad, D., Sekiguchi, K., Shimada, H., Thiele, D., Reeb, D., and Butterworth, D.S. 2003. The abundance of blue whales on the Madagascar Plateau, December 1996. J. Cetacean Res. Mgmt 5 (3): 253-260.

Branch, T.A., Stafford, K.M., Palacios, D.M., Allison, C., Bannister, J.L., Burton, C.L.K., Cabrera, E., Carlson, C.A., Galletti Vernazzani, B., Gill, P.C. and Hucke‐Gaete, R., 2007. Past and present distribution, densities and movements of blue whales Balaenoptera musculus in the Southern Hemisphere and northern Indian Ocean. Mammal Review, 37(2), pp.116-175.

Cerchio S, Trudelle L, Zerbini AN, Charrassin JB, Geyer Y, Mayer FX, Andrianarivelo N, Jung JL, Adam O, Rosenbaum HC. 2016. Satellite telemetry of humpback whales off Madagascar reveals long range movements of individuals in the Southwest Indian Ocean during the breeding season. Marine Ecology Progress Series 562, 193-209.  DOI:10.3354/meps11951.

Cerchio, S., Laran, S., Andrianarivelo, N., Saloma, A., Andrianantenaina, B., Van Canneyt, O. and Rasoloarijao, T., 2022. Cetacean species diversity in Malagasy waters. The New Natural History of Madagascar, p.411.

Fossette, S., Heide-Jørgensen, M.P., Jensen, M.V., Kiszka, J., Bérubé, M., Bertrand, N. and Vély, M., 2014. Humpback whale (Megaptera novaeangliae) post breeding dispersal and southward migration in the western Indian Ocean. Journal of Experimental Marine Biology and Ecology, (450), pp.6-14.

Gambell, R., Best, P.B. and Rice, D.W. 1975. Report on the international Indian Ocean whale marking cruise 24 November 1973- 3 February 1974. Rep. int. Whal. Comm 25: 240 252.

Kasuya, T., Wada, S. 1991. Distribution of large cetaceans in the Indian Ocean: data from Japanese sighting records, November-March. In: S. Leatherwood and G. P. Donovan, eds. Cetaceans and cetacean research in the Indian Ocean sanctuary. Marine Mammal Technical Report No. 3. UNEP, Nairobi, Kenya. Pp 139-170

Kawamura, A. (1980). Food habits of the Bryde’s whales taken in the South Pacific and Indian Oceans. Sci. Reports Whales Res. Inst. 32, 1–23.

Ohsumi, S. (1980). Population study of the Bryde’s whale in the southern hemisphere under scientific permit in the three seasons 1976/77–1978/79. Rep. Int. Whal. Comm. 30, 319-331


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