Dhofar IMMA
Size in Square Kilometres
19 168 km2
Qualifying Species and Criteria
Indian Ocean blue whale – Balaenoptera musculus indica
Criterion A; C (2)
Bryde’s whale – Balaenoptera edeni
Criterion A; C (1, 2)
Humpback whale – Megaptera novaeangliae
Criterion A; B (2); C (1,2)
Sperm whale – Physeter macrocephalus
Criterion C (1,2)
False killer whale – Pseudorca crassidens
Criterion C (1)
Indian Ocean humpback dolphin – Sousa plumbea
Criterion A
Marine Mammal Diversity
Criterion D (2)
Balaenoptera edeni, Balaenoptera musculus indica, Delphinus delphis tropicalis, Globicephala macrorhynchus, Grampus griseus, Kogia sima, Megaptera novaeangliae, Orcinus orca, Peponocephala electra, Physeter macrocephalus, Pseudorca crassidens, Sousa plumbea, Stenella longirostris, Steno bredanensis, Tursiops aduncus, Tursiops truncatus, Ziphius cavirostris
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Summary
The waters off the coast of the Dhofar region of Southern Oman are characterized by dynamic oceanographic conditions strongly influenced by summer and winter monsoons. The summer monsoon creates strong upwelling conditions and high levels of primary productivity between the months of May and September. Highly variable bathymetry in the IMMA comprises wide protected bays and islands on the edge of the continental shelf as well as steep slopes that plummet to great depths. This variety provides a range of highly productive habitats for a diverse array of cetacean species. The area has been documented as a ‘hotspot’ for Endangered Arabian Sea humpback whales (Megaptera novaeangliae). This sub-population is the only known non-migratory population in the world – remaining in the Arabian Sea year-round to both feed and breed. Individually identified humpback whales in the Dhofar IMMA demonstrate a high degree of site fidelity, as well as behaviours associated with both feeding and reproduction (singing males and mothers with calves). In total 17 cetacean species have been observed in the region thus far, ranging from resident nearshore communities of Endangered Indian Ocean humpback dolphins (Sousa plumbea) and Indo-Pacific bottlenose dolphins (Tursiops aduncus) to deep-diving species such as Risso’s dolphins (Grampus griseus), rough toothed dolphins (Steno bredanensis) and Cuvier’s beaked whales (Ziphius cavirostris). Recent sightings and acoustic data suggest the area is also likely to be important for Northern Indian Ocean blue whales (Balaenoptera musculus).
Description of Qualifying Criteria
Criterion A – Species or Population Vulnerability
The Arabian Sea humpback whale (ASHW) population is the only known population of humpback whales not to undertake long-range migrations between low-latitude breeding grounds and high-latitude feeding grounds (Mikhalev 1997, Minton, Collins, et al. 2011). The population is genetically isolated and distinct (Pomilla, Amaral, et al. 2014), and mark-recapture estimates generated from photo identification studies off the coast of Oman are fewer than 100 individuals (82 individuals 95% CI 60-111), providing the rationale for an IUCN Red list status of Endangered (Minton et al. 2008). Dedicated field surveys, satellite tracking and passive acoustic monitoring have confirmed that the Dhofar area is one of the most important habitats for this population in Oman’s waters. Within the Dhofar area, the highest density of sightings, vocalizations and occupancy (as evidenced by satellite tracks and localized behaviour) is concentrated in the Hallaniyats Bay (Minton et al. 2011; Baldwin et al. 2011; Willson et al. 2012; Willson et al. 2013; Willson et al. 2014; Willson et al. 2015; ESO, 2018; Supreme Council, 2019; Cerchio et al. 2018). Indian Ocean humpback dolphins (Sousa plumbea) are also observed in the Dhofar area and wider Arabian Sea Coast with a strong preference for near-shore shallow coastal habitat. Encounters were made around Hasik Bay and southwest of Salalah (Minton et al. 2011) although sightings have also been documented in intervening areas. The species is listed as Endangered on the IUCN Red List (Braulik et al., 2017).
Criterion B: Distribution and Abundance
Sub-criterion B2: Aggregations
Modelling of humpback whale sightings data in relation to survey effort using spatial eigenvector filtering to account for spatial autocorrelation, as well as results of satellite telemetry studies, confirm that the higher relative densities of whales in the Dhofar area are a reflection of their behaviour and not only survey effort (Corkeron et al. 2011, Willson et al. 2016, 2017, 2018). The aggregations have been associated with feeding and breeding behaviour and in one survey period these activities were observed concurrently (Baldwin et al. 2011; Willson et al. 2011).
Criterion C: Key Life Cycle Activities
Sub-criterion C1: Reproductive Areas
Passive acoustic monitoring has documented the presence of ASHW song between November and the end of May (Cerchio et al. 2016; Cerchio et al. 2018). Further breeding-related behaviour has been observed in the form of competitive groups off Ras Hasik (Baldwin et al. 2011). Mother and calf pairs have been observed in the Dhofar area on 7 occasions between 2000 and 2014 (ESO, 2018).
Sub-criterion C2: Feeding Areas
Bubble-net feeding by ASHWs has been documented within the Hasik/Hallaniyats Bay (Baldwin et al. 2011) along with 17 other feeding events recorded in the area between 2001 and 2017 (ESO, 2018). Feeding records also exist for other species including Bryde’s whales, false killer whales, common dolphins, both common and Indo-Pacific bottlenose dolphins and Indian Ocean humpback dolphins (ESO, 2018).
Criterion D: Special Attributes
Sub-criterion D2: Diversity
The diversity in this area includes a range of species exhibiting different ecological preferences, with some species exploiting near shore shallow habitats (e.g. humpback dolphins) and others offshore habitats (e.g. Cuvier’s beaked whales). The range of species also represents species feeding at different trophic levels, from baleen whales to top predators, such as killer whales and false killer whales. Review of sightings data suggests that Ras Nus marks the westernmost extent of humpback dolphin records with a lack of sightings between this point westwards to Mirbat (ESO, 2018). A minimum of 17 cetacean species have been confirmed to occur in the Dhofar area, and dwarf sperm whales are suspected to occur. The list of confirmed species includes: Common dolphin (Delphinus delphis tropicalis), Common bottlenose dolphin (Tursiops truncatus), spinner dolphin (Stenella longirostris), Indo-Pacific bottlenose dolphin (Tursiops aduncus), rough-toothed dolphin (Steno bredanensis), Indian Ocean humpback dolphin (Sousa plumbea), Risso’s dolphin (Grampus griseus), false killer whale (Pseudorca crassidens), killer whale (Orcinus orca), dwarf sperm whale (Kogia sima), melon-headed whale (Peponocephala electra), short-finned pilot whale (Globicephala macrorhynchus), Cuvier’s beaked whale (Ziphius cavirostris), sperm whale (Physeter macrocephalus), Bryde’s whale (Balaenoptera edeni), humpback whale (Megaptera novaeangliae) and Northern Indian Ocean blue whale (Balaenoptera musculus indica). This diverse assemblage of 18 species has been recorded between ‘Ras Nus’ and Ras Hasik (Minton et al. 2011; Baldwin et al. 2011; Willson et al. 2012; Willson et al. 2013; Willson et al. 2014; Willson et al. 2015; ESO, 2018; Supreme Council, 2019).
Supporting Information
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