Comoros Island Chain and Adjacent Reef Banks IMMA

Criterion A – Species or Population Vulnerability

This region is a critical habitat for several threatened marine mammal species (particularly the sperm whale, the Indian Ocean humpback dolphin and the dugong), and a migratory corridor for blue whales (Kiszka et al. 2007a, 2007b, 2010a, 2010b, Pusineri et al. 2013). Information on the movements and distribution of sperm whales in this region remain scarce, but multiple sightings between Mayotte and Anjouan suggest the presence of an aggregation (Van Canneyt et al. 2010). Dugongs still occur in the Comoros, especially in the Mohéli Marine Park, but in small numbers (WWF EAME 2004; Muir & Kiszka 2012). Dugongs occur in small numbers in the lagoon of Mayotte although this species has declined since the early 80’s due to hunting and as bycatch in several fisheries. Probably less than 10 individuals are present throughout the lagoon (Kiszka et al. 2007b, Pusineri et al. 2013). Blue whales (Balaenoptera musculus) have been recorded on several occasions all year round, particularly off Mayotte (Kiszka et al. 2007a, J. Kiszka, unpublished data).

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations 

Small resident populations of coastal dolphins occur, particularly the Indo-Pacific bottlenose dolphin (Tursiops aduncus) and the endangered Indian Ocean humpback dolphin (Sousa plumbea) around Mayotte (Kiszka et al., 2010b, 2012). Using photo-identification data, from 2004 to 2008, estimated annual abundances of bottlenose dolphins ranged from 47 ±18 to 98 ±50 individuals, suggesting low population size across its range around the island (estimated population home range is 978 km², Pusineri et al. 2014). Indian Ocean humpback dolphins only occur in the lagoon of Mayotte, and less than 5 individuals currently remain in the area (J. Kiszka unpublished data). Some evidence suggests that spinner dolphins occurring around some islands are resident, particularly around Mayotte (Viricel et al. 2016). However, more work is required to improve our knowledge on the residency and movements of this species. Finally the area supports a small, resident and isolated population of dugongs, dependent upon seagrass beds for foraging, particularly around Mayotte and in Mohéli (Muir and Kiszka 2012).

Sub-criterion B2: Aggregations

Throughout the area, high densities of oceanic delphinids have been recorded, particularly the spinner dolphin (Stenella longirostris), the pantropical spotted dolphin (Stenella attenuata) and the melon-headed whale (Peponocephala electra) (Kiszka et al., 2010a, 2010b, Laran et al. 2017). Other common species include the sperm whale (Physeter macrocephalus), the short-finned pilot whale (Globicephala macrorhynchus) and the false killer whale (Pseudorca crassidens) (Kiszka et al. 2010a, 2010b). During aerial surveys conducted in 2009-2010 in the region, a relatively dense patch of sightings of sperm whales has been recorded between the islands of Anjouan and Mayotte (off-effort sighting data, Van Canneyt et al. 2010).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

This region is a migratory destination for humpback whales (Megaptera novaeangliae) between July and October (austral winter), where the majority of encountered groups are mother-calf pairs (Kiszka et al. 2010a, Ersts et al. 2011). The high proportion of mother-calf pairs suggests that the surrounding waters of Mayotte, the Geyser/Zélée reef complex, Glorieuses and the other Comorian islands constitute a nursing ground for this species in the region (Globice 2005, Kiszka et al. 2010a, Ersts et al. 2011). Densities of humpback whales is particularly high off the south coast of Moheli, in the coastal waters of Grande Comore and on the Geyser/Zélée complex (Kiszka et al. 2010a, Ersts et al. 2011).The densities of humpback whales on the Iris, Zélée and Geyser banks ranged from 0.027 to 0.618 whales/nm² across three reef banks in 2002 and 2003 (Ersts et al. 2011). Presumably all other species described as being present year-round also reproduce in the area.

Sub-criterion C3: Migration Routes

The region is a known breeding ground for humpback whales during the austral winter (see above), but also a potential migratory corridor for other baleen whales and male sperm whales. Sightings of blue whales in August 2016 and April 2007 (Kiszka et al. 2007) suggest that blue whales migrate through the Comoros archipelago.

Criterion D: Special Attributes

Sub-criterion D2: Diversity

The diversity of species present in the area is sustained by a high variation of ocean, coastal, reef and lagoon habitats, with 22 species of cetaceans recorded and the dugong (Kiszka et al. 2010a, 2010b, Laran et al. 2017). These cetacean species include sperm whale (Physeter macrocephalus), humpback whale (Megaptera novaeangliae), blue whale (Balaenoptera musculus), indo-Pacific and common bottlenose dolphins (Tursiops aduncus, Tursiops truncates), spinner dolphin (Stenella longirostris), pantropical spotted dolphin (Stenella attenuata), Indian Ocean humpback dolphin (Sousa plumbea), melon-headed whale (Peponocephala electra), short-finned pilot whale (Globicephala macrorhynchus), false killer whale (Pseudorca crassidens), Risso’s dolphin (Grampus griseus), pygmy killer whale (Feresa attenuata), Fraser’s dolphin (Lagenodelphis hosei), killer whale (Orcinus orca), Longman’s beaked whale (Indopacetus pacificus), Cuvier’s beaked whale (Ziphius cavirostris), Blainville’s beaked whale (Mesoplodon densirostris), pygmy sperm whale (Kogia breviceps), dwarf sperm whale (Kogia sima), dugong (Dugong dugon), striped dolphin (Stenella coeruleoalba), and rough-toothed dolphin (Steno bredanensis).