Oman Arabian Sea IMMA

Criterion A – Species or Population Vulnerability

The Arabian Sea humpback whale sub-population is listed as ‘Endangered’ on the International Union for the Conservation of Nature (IUCN) Red List based on a mark-recapture population estimate of 82 individuals (95% CI 60-111; Minton et al. 2008), as well as the sub-population’s documented genetic distinctiveness and isolation from other neighbouring sub-populations in the Indian Ocean (Pomilla et al., 2014). While the Dhofar region (Hallaniyats Bay) and the Gulf of Masirah (GOM) have been identified as core hotspots for feeding and reproduction, Arabian Sea humpback whales (Megaptera novaeangliae) have been documented using almost the full range of this humpback highway through direct observation during dedicated cetacean surveys, satellite tracking and passive acoustic monitoring (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, 2019; Cerchio et al. 2016, Cerchio et al. 2018)

Criterion B: Distribution and Abundance

Sub-criterion B2: Aggregations

The Arabian Sea humpback whale subpopulation is the only known population of humpback whales that does not engage in a large-scale migration between low-latitude breeding grounds and high latitude feeding grounds.  It is genetically distinct and geographically isolated, and thus represents a highly distinct sub-population. Boat-based surveys coupled with acoustic surveys, satellite telemetry and photo-identification studies indicate that the Oman Arabian Sea Coast EBSA, with slightly expanded boundaries, encompasses the most important habitat for Oman’s Arabian Sea humpback whales.  While two of 14 tagged whales left the boundaries of the area, the majority stayed within these boundaries throughout the duration of their tag transmission (Willson et al. 2016, 2018).  Furthermore, a high rate of photo-identification re-sights between the Gulf of Masirah and Dhofar both within years and between years indicates that while some whales may engage in longer-range movements to Yemen and/or India, at least a portion of the sub-population seems to remain on the Arabian Sea coast of Oman year-round and in multiple years (Minton et al. 2011, Willson et al. 2016, 2018).  Additionally, mark-recapture estimates based on the same photo-identification data collected off the coast of Oman between 2000 and 2004 indicate that fewer than 100 individuals were using the habitats encompassed in the area (Minton et al. 2008; Minton et al 2011.). 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 and Gulf of Masirah areas 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.2012).  While densities of whales in these areas may be lower than those on other humpback whale breeding and feeding grounds, the densities recorded here are higher than any other area in the Arabian Sea humpback whales’ range to date, and the areas clearly serve the same purpose as feeding and breeding grounds do for the species elsewhere.

Criterion C: Key Life Cycle Activities

Sub-criterion C3: Migration Routes

Location and track data derived from the satellite telemetry revealed a predominance of localized behaviour and transits between the Hallaniyats Bay area and the Gulf of Masirah. Transitory movements of humpback whales through the Dhofar area have been revealed by behaviour mode index of static space state modelling of satellite telemetry data. These records are noted from five of 14 Arabian Sea humpback whales instrumented with tags in the Dhofar and Gulf of Masirah areas between 2014 and 2015 (Willson et al. 2016). Habitat utilization kernel density estimates indicate high site fidelity for the majority of tagged individuals (Willson et al., 2016, Willson et al., 2015, Willson et al., 2018).  Only two of the 14 tagged individuals moved outside of Omani waters and the area bounded by this area. Of these two, one male, remained mostly within the boundaries of the area but moved further southwest into Yemeni waters. The other, a female, crossed the Arabian Sea to the southern tip of India, but then returned to the Gulf of Masirah where she was originally tagged (Willson et al., 2016, Willson et al., 2018). The documented movement between Oman and India, coupled with an increasing number of sightings and recordings of song documented from the coasts of Pakistan and India, provides evidence that some proportion of the Arabian Sea humpback whale population is using the eastern portion of the Arabian Sea as well as Oman’s coast. The Oman Arabian Sea area encompasses the most heavily used habitat for whales that are present, year-around, off of Oman’s coast.