Muscat Coastal Waters and Offshore Canyons IMMA

Criterion C: Key Life Cycle Activities

Sub-criterion C1: Reproductive Areas

Ponnampalam (2009) reports that calves were observed in 77% (n=133) of all cetacean groups observed during dedicated cetacean surveys conducted in the Muscat area between 2004 and 2006.  Calves were most frequently seen in spinner dolphin (n=55), common dolphin (n=32), and bottlenose dolphin (n=33) groups.   These three species are observed in all months of the year in the Muscat area (Minton et al., 2010b, Minton, 2004a, Ponnampalam, 2009, Environment Society of Oman, 2019). While no photo-identification or genetic sampling studies have been conducted to confirm residence of the same individuals, the regularity of their presence and the frequency with which these species are observed with calves provides strong evidence that the Muscat area is important for these species’ reproduction.

Sub-criterion C2: Feeding Areas

Oceanographic data from the Muscat area indicates that it is a highly productive region supporting a thriving artisanal fishery (Al-Oufi et al., 2000). Seven of the 14 species observed in the Muscat Area have been observed feeding in the area.  Spinner dolphins and common dolphins frequently occur in mixed species groups of 100 individuals or more (Minton et al., 2010b, Minton, 2004a, Ponnampalam, 2009, Environment Society of Oman, 2019), often also in association with artisanal fishing boats using baited handlines to fish for yellowfin tuna in among large schools of Sardinella longiceps.  Behaviour of dolphins in these groups was often consistent with feeding (long dives, fast direction changes), although direct feeding was not always observed. Ponnampalam et al. (2012) documented the stomach contents of stranded spinner and bottlenose dolphins found in the Muscat area.  In the case of spinner dolphins, myctophids (lanternfish species) comprised the most represented prey family in terms of number and frequency of occurrence (99.4% and 100.0% respectively for the two specimens examined), although cephalopods were also present in one specimen. Myctophids are generally found in the mesopelagic layer of deeper waters, which can be found closer to shore in the Muscat area than in the area further to the north where the continental shelf is wider. Ponnampalam et. al concluded that spinner dolphins were most likely feeding in the deeper waters at night, and migrating closer inshore during the day, as is common for the species in other areas where it has been studied (e.g. Benoit-Bird and Au, 2003, Ponnampalam et al., 2012, Tyne et al., 2017). The same study documented the stomach contents of a single specimen of Tursiops truncatus stranded in the Muscat area, and also revealed a predominance of deep-water prey species – in this case cephalopods associated with the mesopelagic layer (Ponnampalam et al., 2012). Stomach content analysis was not available for other species observed live or stranded in the Muscat area.  However, both common dolphins and Bryde’s whales have been observed regularly in association with shoaling sardines, in some cases lunge feeding among them (Minton unpublished data, Collins unpublished data, Environment Society of Oman 2019). Risso’s dolphins, sperm whales, and false killer whales, have also either been observed feeding, or are presumed to feed in the area based on their known prey and feeding habitats in other parts of their global range, where they are known to be associated with shelf edges and nearshore canyons and gullies, such as those found in the Muscat area (e.g. Azzellino et al., 2008, Baird, 2018, Cañadas et al., 2002).

Criterion D: Special Attributes

Sub-criterion D2: Diversity

The Muscat area includes a range of habitats, including wide sandy coastal shelves, sheltered rocky embayment, and steeply shelving deep-water canyons close to shore. This diversity in habitats supports a range of cetacean species, some of which are confirmed to be resident year round. Fourteen cetacean species have been observed live at sea in the Muscat area according to the Oman Cetacean Database (OMCD), curated by the Environment Society of Oman. This database includes observations documented from the 1960s onward, ranging from incidental observations made by qualified observers during the course of other coastal/marine work, to those made during dedicated cetacean surveys.  Records in the OMCD include those from a series of surveys conducted between 2001 and 2003, and analysed as part of  a PhD thesis by G. Minton (2, 264km/104 hours of search effort) (Minton, 2004a), and those made during a series of surveys between 2004 and 2006 and analysed as part of a PhD thesis by L. Ponnampalam (2610.4km/112.3 hours of search effort) (Ponnampalam, 2009). The five most frequently observed species in both studies and in the Oman Cetacean Database as of 2019 are (in order of frequency), spinner dolphins, common dolphins, bottlenose dolphins, Risso’s dolphins, and Bryde’s whales, which were all represented by over 50 sightings each (Ponnampalam, 2009, Minton, 2004a, Environment Society of Oman, 2019).  As described above, Spinner, common and bottlenose dolphins are likely to be both feeding and breeding in the area, while Risso’s dolphins and Bryde’s whales are likely feeding. False killer whales were the next most regularly observed species (25 recorded observations), and when their behaviour could be accurately classified, they were most often traveling.  Sperm whales were observed on 14 occasions, including a documented observation of 35 individuals in a marguerite formation and in association with Risso’s and bottlenose dolphins (Ponnampalam, 2016). Ten observations of Arabian Sea humpback whales have been recorded in the Muscat Area, including two animals that were entangled in fishing gear and released through human intervention (Environment Society of Oman 2019). By applying spatial eigenvector filtering to models based on baleen whale sightings data collected in Oman through 2004, Corkeron et al. (2011) determined that while the Arabian Sea coast of Oman was more important habitat for Arabian Sea humpback whales, the Muscat Area was of higher relative importance for Bryde’s whales. Other species with fewer than 10, but more than 2 documented observations at sea include blue whales, pantropical spotted dolphins and dwarf sperm whales.  Striped dolphins were documented in the Muscat area only once (Environment Society of Oman 2019).  Species that would be expected to be observed in deeper offshore waters are most likely under-represented in the Oman Cetacean Database, as survey effort and incidental sightings are concentrated in nearshore waters.  Perhaps surprisingly, to date bottlenose dolphin sightings in the Muscat area comprise only sightings of T. truncatus, with no confirmed sightings of T. aduncus, although this smaller tropical species is observed further south on the Arabian Sea coast of Oman. Strandings documented in the Muscat Area through 2002 reflect the same species composition and relative abundance/frequencies as those documented through live sightings, with spinner and common and bottlenose dolphins being the most frequently observed stranded species (e.g. Collins et al., 2002).