South West Madagascar and Mozambique Channel IMMA

Criterion A – Species or Population Vulnerability

Antarctic blue whales (Balaenoptera musculus intermedia) classified as Critically Endangered, and pygmy blue whales (B. m. brevicauda) classified as Endangered are both known to occur in the area during the austral summer (Anderson et al, 2012, Cerchio et al. 2018, Cerchio unpublished data). The Vulnerable sperm whale (Physeter macrocephalus) is located in deep-water habitats, whilst the Endangered Indian Ocean humpback dolphin (Sousa plumbea) is encountered in coastal areas, and to mitigate further decline of this species, conservation measures were recommended against direct hunting reported in the area (Cerchio et al. 2015)

Criterion C: Key Life Cycle Activities

Sub-criterion C3: Migration Routes

Antarctic blue whales (Balaenoptera musculus intermedia) occur in the tropical and subtropical Indian Ocean, and were estimated to 2,300 individuals (1,150 – 4,500) in the Southern Hemisphere IWC (2007). Based upon the presence of Antarctic blue whale song off the northwest coast of Madagascar during the austral winter (Cerchio et al. 2018), it is certain that the species migrate through this area. In the SWIO, a population of pygmy blue whales (Balaenoptera musculus brevicauda) is defined by the “Madagascar” song-type, heard from the Madagascar Ridge to the central Indian Ocean (McDonald et al. 2006, Samaran et al 2013). There is a likely summer feeding region on the Madagascar Ridge, for which abundance was estimated at 424-474 (Best et al. 2003). Based upon the bimodal presence of SWIO pygmy blue whale song off the northwest coast of Madagascar during the austral spring and autumn (Cerchio et al. 2018), it is certain that the species migrates through this area. Recent passive acoustic monitoring from the southwest coast of Madagascar (Toliara) has confirmed the presence of Antarctic blue whale song during at least the austral autumn, and SWIO pygmy blue whale song during at least the austral summer and autumn seasons (Cerchio, unpublished data). Given the potential for blue whale song to propagate long distances (in excess of 100km) it is likely that these animals were moving through the offshore extent of the IMMA.  In addition to the two blue whale subspecies, fin whales (Balaenoptera physalus), and Antarctic minke whales (B. bonaerensis) were also detected during the austral spring/summer (Cerchio, unpublished data) likely on migration through this area, as they have also been acoustically detected off northwest Madagascar during the austral winter (Cerchio et al. 2018).

Criterion D: Special Attributes

Sub-criterion D2: Diversity

More than 18 species have been documented in this area through aerial surveys (Van Canneyt et al, 2010) and acoustic monitoring (Cerchio et al. 2018, Cerchio unpublished data). Most abundant species were large Delphininae (mostly common and some Indo-Pacific bottlenose dolphins) and small Globicephalinae (mostly melon headed whale, Laran et al, 2017). The taxonomic richness for this candidate area predicted from occupancy analyse of marine mammals (see Laran et al., 2017) is among maximum values obtained for the region. During REMMOA aerial surveys, the most abundant species were large Delphininae, mostly common and some Indo-Pacific bottlenose dolphins (Tursiops spp.) with a relative density of 17 x 10-2 individuals.km² (CV = 28%) in the area and small Globicephalidae (mostly melon headed whale, Peponocephala electra) with 6.3 x 10-2 individuals.km² (CV: 72%). Large Globicephalidae, mostly false killer whale (Pseudorca crassidens) and some short-finned pilot whale (Globicephala macrorhynchus) had a relative density of 3 x 10-2 individuals.km² (CV: 41%) and Risso’s dolphin with 3 x 10-2 individuals.km² (CV:41%). For deep divers, the highest density in this area were obtained for beaked whales (Cuvier’s’ beaked whale, Ziphius cavirostris and Blainville’s beaked whale, Mesoplodon densirostris) with 0,6 x 10-2 individuals.km² (CV: 56%), while sperm whale and Kogia spp. were estimated each with one order of magnitude less (without correcting for the availability bias due to dive duration of this species). Small Delphininae (Stenella spp.) were also significant in the area with relative density of 2,6 x 10-2 individuals.km² (CV = 41%, Laran et al, 2017). In the coastal waters the Indian Ocean humpback dolphin (Sousa plumbea) is encountered with direct hunting reported in the area (Cerchio et al, 2015). Other species as stripped dolphin (Stenella coeruleoalba), pygmy killer whale (Feresa attenuata) and killer whale (Orcinus orca) were encountered occasionally.