Madagascar Central East Coast IMMA
Size in Square Kilometres
55 524 km2
Qualifying Species and Criteria
Humpback whale – Megaptera novaeangliae
Criterion B (2); C (1, 3)
Marine Mammal Diversity
Feresa attenuata, Indopacetus pacificus, Megaptera novaeangliae, Peponocephala electra, Physeter macrocephalus, Pseudorca crassidens, Tursiops aduncus, Tursiops truncatus, Ziphius cavirostris
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The Madagascar Central East Coast IMMA encompasses Antongil Bay, the waters off Île Sainte-Marie, the narrow continental shelf past the port city of Toamasina (Tamatave) and waters beyond the continental shelf edge up to approximately 50km offshore. The area comprises important habitat for breeding aggregations of humpback whales (Megaptera novaeangliae), with mother–calf pairs showing a strong preference for shallow waters within Antongil Bay. The IMMA also hosts migrating humpback whales, with demonstrated connectivity to several other breeding grounds and migration routes, including those in the Mascarenes, northwest Madagascar, southern Madagascar, the Comoros Archipelago, and eastern Africa. Diversity and densities of other species within the area are observed to be relatively moderate for the region; however, Vulnerable sperm whales (Physeter macrocephalus) and beaked whale species have been observed in association with the 2000 m isobath.
Description of Qualifying Criteria
Criterion B(2) – Aggregations
The area represents an important aggregation area for breeding humpback whales. Breeding hotspots (aggregations) were determined from kernel density models of satellite telemetry data to exist of Ile Sainte Marie, including in the Sainte Marie Channel, and the waters of the continental shelf south of Ile Sainte Marine to the Mongoro River mouth (Dulau et al. 2017). Similarly, Cerchio et al. (2016) identified the same general area as an area of “localized” movement behaviour for whales tagged off Île Sainte-Marie in 2012. These ‘hotspots’ coincide with a relatively shallow area of the continental shelf, which may provide a higher suitability of breeding habitat for this species (Trudelle et al. 2016). While the sample size of satellite tagged animals is relatively small compared to the size of the population (although comparative with other satellite telemetry studies for this species), research suggests that humpback whales have a strong tendency to aggregate when conspecifics are detected (e.g., by song), especially now populations have been diminished by whaling (Clapham et al. 2015). As such, a breeding ‘hotspot’ indicated by only a few animals through satellite telemetry data may represent a more significant aggregation area as other animals are attracted to the site.
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
The southwest Indian Ocean represents breeding and migratory habitat for humpback whale “Breeding Stock C,” as defined by the International Whaling Commission. Breeding Stock C is further divided into four “breeding substocks” (i.e., “BSC1-C4”). Breeding Substocks C3 and C4 are known to aggregate in the coastal waters of central eastern Madagascar, including Antongil Bay, Île Sainte-Marie, and the waters south to the Mongoro River mouth during the winter (Rosenbaum et al. 1997; Best et al. 1998; Ersts and Rosenbaum 2003; Cerchio et al. 2009; Best and Brandão 2009; Cerchio et al. 2016; Trudelle et al. 2016; Dulau et al. 2017; Trudelle et al. 2018). Following preliminary surveys in 1996, Rosenbaum et al. (1997) described Antongil Bay as a breeding area for humpback whales in the southwestern Indian Ocean. Behaviours widely accepted to indicate breeding activity were regularly sighted, including males singing and exhibiting competitive behaviour, and females with young calf (Pomilla & Rosenbaum 2006). Humpback whales have generally been observed in Antongil Bay from June to October, with the highest concentrations occurring in July through early September (Rosenbaum et al. 1997; Cerchio et al. 2009). Photographic mark-recapture data indicated that humpback whales utilizing Antongil Bay between 2000 and 2006 had low recapture rates with short residency times; therefore whales appeared to regularly move through the bay with transient residency as part of a more extensive breeding range for a large population, estimated to be in excess of 6000 animals in 2006 (Cerchio et al. 2009). More recently, satellite telemetry data of humpback whales tagged off Île Sainte-Marie (N=12) in 2012, Anakao in the southwest (N=11), and La Reunion (N=12) in 2013 have highlighted potential breeding ‘hotspots’ off Île Sainte-Marie and the waters south to the Mongoro River mouth, but no entry or usage of Antongil Bay despite substantial use of the Sainte-Marie Channel and areas just east of the Bay mouth (Cerchio et al. 2016; Trudelle et al. 2016; Dulau et al. 2017). These data and other anecdotal observations suggest a reduced usage of Antongil Bay in recent years, and potential change of condition given extensive documentation of high densities in the bay during peak season in previous years (1996 to 2006) (Rosenbaum et al. 1997, Ersts & Rosenbaum 2003, Cerchio et al., 2009).
Sub-criterion C3: Migration Routes
There are clear multiple sources of evidence of extensive humpback whale movements between the area defined by the Madagascar Central East Coast IMMA and other areas surrounding Madagascar, as well as areas off east Africa and the Mascarenes (e.g., Rosenbaum et al. 2009; Ersts et al. 2011; Fossette et al. 2014; Cerchio et al. 2008, 2016; Trudelle et al. 2016; Dulau et al. 2017; Kershaw et al. 2017). More broadly, the area falls within the migratory stream of Breeding Stock C as animals transit annually between productive feeding areas in the Southern Ocean and warmer wintering grounds off East Africa, the Comoros Archipelago, Madagascar, and the Mascarenes.
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Best PB, Brandão A. 2009. Humpback whaling at Madagascar, 1910–1950. International Whaling Commission document SCF09SH2, 22–25 June 2009, Madeira, Portugal.
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Pomilla, C., and Rosenbaum, H.C. 2006. Estimates of relatedness in groups of humpback whales (Megaptera novaeangliae) on two wintering grounds of the Southern Hemisphere. Molecular Ecology 15, 2541-2555.
Rosenbaum HC, Walsh P, Razafindrakoto Y, Vely M, Desalle R. 1997. First description of a humpback whale wintering ground in Baie d’Antongil, Madagascar. Conservation Biology 11: 308–314.
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