Comoros Island Chain and Adjacent Reef Banks IMMA

Size in Square Kilometres

65 900 km2

Qualifying Species and Criteria

Humpback whale – Megaptera novaeangliae

Criterion A; B (2); C (1,3)

Blue whale – Balaenoptera musculus

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

Sperm whale – Physeter macrocephalus

Criterion A; B (2)

Melon-headed whale – Peponocephala electra       

Criterion B (2)

Short-finned pilot whale – Globicephala macrorhynchus

Criterion B (2)

Spinner dolphin – Stenella longirostris

Criterion B (2)

Indo-Pacific Bottlenose dolphin – Tursiops aduncus

Criterion B (1)

Indian Ocean humpback dolphin – Sousa plumbea

Criterion A; B (1)

Pantropical spotted dolphins – Stenella attenuata

Criterion B (2)

False killer whale – Pseudorca crassidens    

Criterion B (2)

Dugong – Dugong dugon      

Criterion A; B (1)

Marine Mammal Diversity 

Criterion D (2)

Physeter macrocephalus, Megaptera novaeangliae, Balaenoptera musculus, Tursiops aduncus, Tursiops truncatus, Stenella longirostris, Stenella attenuata, Sousa plumbea, Peponocephala electra, Globicephala macrorhynchus, Pseudorca crassidens, Grampus griseus, Feresa attenuata, Lagenodelphis hosei, Orcinus orca, Indopacetus pacificus, Ziphius cavirostris, Mesoplodon densirostris, Kogia breviceps, Kogia sima, Dugong dugon, Stenella coeruleoalba, Steno bredanensis


The   Comoros Island chain includes Grande Comore, Mohéli, Anjouan, Mayotte and two reef banks under French jurisdiction (the Zélée/Geyser complex and the Glorieuses).  The diverse habitats in the IMMA  include shallow protected lagoons and fringing reefs around islands, as well as deep oceanic waters,  submarine canyons and seamounts between the main islands. These habitats support a total of 22 documented cetacean species as well as a small population of dugongs (Dugong dugon).  Small resident populations of coastal dolphins are found around the islands and reefs, including Indo-Pacific bottlenose dolphins (Tursiops aduncus) and endangered Indian Ocean humpback dolphins (Sousa plumbea) around Mayotte. High densities of oceanic delphinids have been recorded throughout the archipelago, with multiple records of spinner dolphins (Stenella longirostris), pantropical spotted dolphins (Stenella attenuata) and melon-headed whales (Peponocephala electra). Other common species include dwarf sperm whales (Kogia sima), Blainville’s beaked whales (Mesoplodon densirostris), sperm whales (Physeter macrocephalus), short-finned pilot whales (Globicephala macrorhynchus), and false killer whales (Pseudorca crassidens). The island chain also serves as a mating, calving and nursing ground for Southern Hemisphere humpback whales (Megaptera novaeangliae). These appear to be most commonly observed off the south coast of Mohéli, in the coastal waters of Grande Comore, and on the Geyser/Zélée complex. Finally, dugongs (Dugong dugon) still occur in small numbers in the Mohéli Marine Park in the southern portion of Mayotte’s lagoon. However, this population has declined greatly over the past four decades.

Description of Qualifying Criteria

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).

Supporting Information

ERSTS, P.J., KISZKA, J., VELY, M. & ROSENBAUM, H.C., 2011. Density, group composition, and encounter rates of humpback whales (Megaptera novaeangliae) in the eastern Comoros archipelago [C2]. Journal of Cetacean Research and Management, 3 (special issue): 175-182.

FOSSETTE, S., HEIDE-JØRGENSEN, M.P., VILLUM JENSEN, M., KISZKA, J., BERUBE, M., BERTRAND, N. & VELY, 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: 6-14.

GLOBICE, 2005. Compte rendu de mission « mammifères marins » des îles Glorieuses, 9-16 aout 2005. 12pp. 

KISZKA, J., 2015. Marine mammals: a review of status, distribution and interaction with fisheries in the Southwest Indian Ocean. Chapter 8: 303-323. In: Van der Elst RP and Everett BI. 2015. (eds). Offshore fisheries of the Southwest Indian Ocean: their status and the impact on vulnerable species. Oceanographic Research Institute, Special Publication, 10. 448pp.

KISZKA, J., ERSTS, P.J. & RIDOUX, V., 2007a. Cetacean diversity around the Mozambique Channel island of Mayotte (Comoros archipelago). Journal of Cetacean Research and Management, 9(2): 105-109.

KISZKA, J., ERSTS, P.J. & RIDOUX, V., 2010b. Structure of a toothed cetacean community around a tropical island (Mayotte, Mozambique Channel). African Journal of Marine Science, 32(3): 543-551.

KISZKA, J., MUIR, C. & JAMON, A., 2007b. Status of a marginal dugong (Dugong dugon) population in the lagoon of Mayotte (Mozambique Channel), in the western Indian Ocean. Western Indian Ocean Journal of Marine Science, 6(1): 111-116.

KISZKA, J., SIMON-BOUHET, B., GASTEBOIS, C., PUSINERI, C. & RIDOUX, V., 2012. Habitat partitioning and fine scale population structure among insular bottlenose dolphins (Tursiops aduncus) in a tropical lagoon. Journal of Experimental Marine Biology and Ecology, 416-417: 176-184.

KISZKA, J., VELY, M. & BREYSSE, O., 2010a. A preliminary account of cetacean diversity and humpback whale (Megaptera novaeangliae) group characteristics around the Union of the Comoros (Mozambique Channel). Mammalia, 74: 51-56.

LARAN, S., AUTHIER, M., VAN CANNEYT, O., DORÉMUS, G., WATREMEZ, P. & RIDOUX, V., 2017. A Comprehensive Survey of Pelagic Megafauna: Their Distribution, Densities, and Taxonomic Richness in the Tropical Southwest Indian Ocean. Frontiers in Marine Science4, p.139.

PUSINERI, C., BARBRAUD, C., KISZKA, J., CACERES, S. MOUGNOT, J., DAUDIN, G. & RIDOUX, V., 2014. Capture-mark-recapture modelling suggests an endangered status for the Mayotte Island (eastern Africa) population of Indo-Pacific bottlenose dolphins. Endangered Species Research, 23: 33-43.

VAN CANNEYT, O., DORÉMUS, G., LARAN, S., RIDOUX, V., WATREMEZ, P. 2010. Distribution et abondance de la mégafaune marine dans le sud-ouest de l’océan Indien. Marine Mammal Research Centre, AAMP. 70pp.

VIRICEL, A., SIMON-BOUHET, B., CEYRAC, L., DULAU-DROUOT, V., BERGGREN, P., AMIR, O.A., JIDDAWI, N., MONGIN, P. & KISZKA, J., 2016. Habitat availability and geographic isolation as potential drivers of the genetic population structure in an oceanic dolphin in the southwest Indian Ocean. Marine Biology, 163: 219.


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