Maldives Archipelago and Adjacent Oceanic Waters IMMA

Size in Square Kilometres

166 500 km2

Qualifying Species and Criteria

Humpback whale – Megaptera novaeangliae

Criterion A; C (1); D (2)

Northern Indian Ocean blue whale – Balaenoptera musculus indica

Criterion A; C (3)

Sperm whale – Physeter macrocephalus

Criterion A

Spinner dolphin – Stenella longirostris

Criterion C (2, 3)

Pantropical spotted dolphin – Stenella attenuata

Criterion C (2)

Marine Mammal Diversity 

Criterion D (2)

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

 

Summary

The Maldives comprises a chain of coral atolls in the Equatorial Indian Ocean, southwest of India and Sri Lanka. Running from north to south,  the atolls of the Maldives form the central and largest part of the Lakshadweep-Chagos Ridge, but are separated from those two other archipelagos by deep, wide channels. The Maldives archipelago hosts a variety of habitats, including the atolls themselves, the slopes immediately outside the atolls, the channels and other waters between the atolls, and oceanic waters immediately offshore. These habitats host a diverse array of 23 documented cetacean species.  Spinner dolphins (Stenella longirostris) and pantropical spotted dolphins (Stenella attenuata), are the most frequently observed species, and are known to both feed and reproduce within the area.  Blue whales (Balaenoptera musculus) and humpback whales (Megaptera novaeangliae) have also been observed at regular intervals, and may include visitors from both the Southern Hemisphere and the Arabian Sea.

Description of Qualifying Criteria

Criterion A – Species or Population Vulnerability

The Maldives are at the southern end of the range of the Endangered Arabian Sea sub-population of the humpback whale (Megaptera novaeangliae) population and is within the range of the Northern Indian Ocean Blue Whale (Balaenoptera musculus indica) (Anderson et al., 2012a). Although the status of this subspecies has not been assessed, it was subject to high levels of commercial whaling in the 1960s, and the species as a whole is considered to be Endangered by the IUCN Red List. Sperm whales (Physeter macrocephalus), assessed as Vulnerable, also occur in Maldivian waters; indeed, this species is the one most frequently recorded as stranding in Maldives (Anderson et al., 1999).

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Southern Ocean Humpback Whales (Megaptera novaeangliae) visit Maldives in increasing numbers during June-October. The proportion of sightings with calves increases dramatically in Sept-Oct (RCA pers obs). Several other species are also seen regularly with calves, suggesting that the Maldives is a reproductive area for species such as Spinner Dolphins (Stenella longirostris) and Pantropical Spotted Dolphins (Stenella attenuata) (Anderson, 2005; Dalebout et al., 2003; Anderson et al., 2012b; R.C. Anderson, pers. obs.).

Sub-criterion C2: Feeding Areas

The Maldives are affected by the seasonally oscillating monsoon seasons, which brings two distinct peaks of marine productivity to the archipelago. During the SW monsoon season (April to Oct), ocean currents are from the west, and productivity is high on the eastern side of the atoll chain. During the NE monsoon season (Dec to March), ocean currents are from the east, and productivity is high on the western side of the atoll chain. Many species shift from side to side of the atolls to take advantage of this seasonally shifting abundance of food. This is most obvious for those species closely associated with the outer atoll slopes. The blue whale is the commonest on the seasonally changing upstream side of the Maldives atoll chain, whilst In contrast spinner dolphins appear to be commonest on the downstream side of the atolls (Anderson, 2005; Anderson et al., 2011 & 2012a; RCA pers obs). The waters of the far north of the Maldives appear to be a seasonal feeding ground of particular importance for pantropical spotted dolphins (Anderson et al., 2011).

Sub-criterion C3: Migration Routes

The Maldives are on the migration route of the Northern Indian Ocean blue whales, as they pass seasonally between Sri Lanka and the upwelling areas of the Arabian Sea (Anderson et al., 2012a), their numbers peaking in Dec-Jan and again in April. The far north of the Maldives may be a particularly important migratory corridor, with increasing numbers of humpback whales are recorded each year in June-October (R.C. Anderson, pers. obs.). These are believed to be Southern Ocean animals, at the northern end of their annual migration. Large numbers of spinner dolphins appear to constantly pass through the Maldives. Movements are generally upstream (i.e. into the seasonally changing monsoon currents) although further details of these movements are not known (R.C. Anderson, pers. obs.).

Criterion D: Special Attributes

Sub-criterion D2: Diversity

A total of 23 species of cetacean have been recorded from the Maldives, with many of these species occurring in relatively high densities relative to surrounding areas in India and Sri Lanka (Ballance et al., 2001; Anderson, 2005; Anderson et al., 2015; RCA pers obs). Within a 10-day survey period encounters of 10-12+ species are commonly recorded (Anderson et al., 2015), including striped dolphin, rough-toothed dolphin, Fraser’s dolphin, common bottlenose dolphin, killer whale, melon-headed whale, false killer whale, pygmy killer whale, and Bryde’s whale, During the 5-year round-the-world Voyage of the Odyssey, acoustic detections were recorded consistently, and the Maldives had the highest detection rates recorded for the entire voyage, suggesting particularly high abundance of cetacean species and their diversity (Voyage of the Odyssey, 2009; Clark et al., 2012).

Supporting Information

Anderson, R.C. 2005. ‘Observations of cetaceans in the Maldives, 1990-2002’. Journal of Cetacean Research and Management, 7(2): 119-135.

Anderson, R.C. 2014. ‘Cetaceans and Tuna Fisheries in the Western and Central Indian Ocean’. IPNLF Technical Report 2, International Pole and Line Foundation, London. 133 pages.

Anderson, R.C., A.Shaan and Z.Waheed. 1999. ‘Records of cetacean ‘strandings’ from the Maldives’. Journal of South Asian Natural History 4(2): 187-202.

Anderson, R.C., R. Clark, P.T. Madsen, C. Johnson, J. Kiszka and O. Breysse. 2006. Observations of Longman’s beaked whale (Indopacetus pacificus) in the western Indian Ocean. Aquatic Mammals, 32(2): 223-231.

Anderson, R.C., M.S. Adam and J.I. Goes. 2011. From monsoons to mantas: seasonal distribution of Manta alfredi in the Maldives. Fisheries Oceanography, 20: 104-113.

Anderson, R.C., T.A. Branch, A. Alagiyawadu, R. Baldwin and F. Marsac. 2012a. Seasonal distribution, movements and taxonomic status of blue whales (Balaenoptera musculus) in the northern Indian Ocean. Journal of Cetacean Research and Management, 12: 203-218.

Anderson, R.C., S.A. Sattar and M.S. Adam. 2012b. Cetaceans in the Maldives: a review. Journal of Cetacean Research and Management, 12: 219-225.

Ballance, L.T., R.C. Anderson, R.L. Pitman, K. Stafford, A. Shaan, Z. Waheed and R.L. Brownell Jr. 2001. Cetacean sightings around the Republic of Maldives, April 1998. Journal of Cetacean Research and Management, 3(2): 213-218.

Clark, R.A., C.M. Johnson, G. Johnson, R. Payne, I. Kerr, R.C. Anderson, S.A. Sattar, C.A.J. Godard and P.T. Madsen. 2012. Cetacean sightings and acoustic detections in the offshore waters of the Maldives during the northeast monsoon seasons of 2003 and 2004. Journal of Cetacean Research and Management, 12(2): 227–234.

Dalebout, M.L., C.S. Scott, G.J.B. Ross, R.C. Anderson, P.B. Best, V.G. Cockroft, H.L. Hinsz, V. Peddemors and R.L. Pitman. 2003. Appearance, distribution and genetic distinctiveness of Longman’s Beaked Whale, Indopacetus pacificus. Marine Mammal Science, 19: 412-461.

Dalebout, M.L., C. Scott Baker, D. Steel, K. Thompson, K.M. Robertson, S.J. Chivers, W.F. Perrin, M. Goonatilake, R.C. Anderson, J.G. Mead, C.W. Potter, L. Thompson, D. Jupiter and T.K. Yamada. 2014. Resurrection of Mesoplodon hotaula Deraniyagala 1963: A new species of beaked whale in the tropical Indo-Pacific. Marine Mammal Science, 30(3): 1081-1108.

Kershaw, F., M.S. Leslie, T. Collins, R.M. Mansur, B.D. Smith, G. Minton, R. Baldwin, R.G. Leduc, R.C. Anderson, R.L. Brownell Jr and H.C. Rosenbaum. 2013. Population differentiation of 2 forms of Bryde’s Whales in the Indian and Pacific Oceans. Journal of Heredity, 104(6): 755-764.

Ocean Alliance. 2009. The Voyage of the Odyssey. Ocean Alliance, Gloucester, Maine. 176pp.

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