Blue Whales in Oman; the Sultanate’s most diverse marine mammal hotspot just got hotter!

The following is a blog shared by ASWN member Andy Willson that provides some insight and inspiration for cetacean conservation efforts off the coast of Oman, based on recent surveys conducted in the Dhofar region.  The results of these surveys were also presented to the International Whaling Commission’s recent Scientific Committee meeting in May, and the more scientific version can be found here.  But for a more informal and entertaining read, pour yourself a cup of tea, and sit down and Enjoy the following!

Blue whale medley April 2019

A blue whale photo medley courtesy of Five Oceans Environmental Services, Oman.

The Five Oceans Environmental Services (5OES) team based in Muscat, Oman spent early April 2019 conducting a cetacean survey off southern Oman. Following on a hot trail of discovery, the recent survey documented blue whales conspicuously feeding in this area for the first time. Maturing in step with the receding hair-lines of its once young explorers, scientific evidence from this study site is beginning to prove that it is one of the most diverse, exciting and confusing areas for cetacean research in the Northern Indian Ocean (NIO).

Formalised cetacean research in Oman took off in the late nineties/early 2000s in response to growing global interest in records of humpback whales off Oman’s coast. Hundreds of kilometres of coastline lay waiting to be explored by a ‘green’ team of early career researchers armed with a shaky old 4WD, a retired fishing boat, a point and shoot 35mm camera and a stash of donated baked beans and pitta bread. Initial records pooled from merchant navy records, incidental sightings and soviet whaling records from the mid-60s provided evidence that the humpbacks found off the coast could be part of a unique and isolated population. With an astonishing talent for establishing scientific collaboration and busking for support, the team’s efforts were rewarded in 2008 with formal recognition that Oman’s humpbacks were indeed an isolated population of humpbacks, and so graduated from their previous designation by the International Whaling Commission (IWC) of ‘Population X’ into a more formal title, ‘Arabian Sea humpback whales’. Years of genetic study, involving biopsying whales to collect tissue samples for subsequent DNA analysis in the lab had proved that the whales were totally different from all other humpbacks in the world and had been isolated for an estimated 70,000 years. At the same time, photo-ID mark-recapture population assessment provided estimates of fewer than 100 animals residing off Oman. This prompted an urgent requirement to answer more questions relating to conservation management. More complex ecological investigations began to emerge in the form of species distribution modelling, round the clock acoustic monitoring and, ultimately, satellite tracking. These new methods required refocusing the team’s very limited survey resources into just two favoured study sites.

Early on, one of these favoured study sites on the corner of the Hallaniyats Bay in southern Oman began to yield results beyond expectations. Almost every survey the area resulted in encounters with new species or observations of new behaviour. At the last count the team which includes the Environment Society of Oman and Ministry of Environment and Climate Affairs had documented 18 of the 21 species known to Oman. At first look the guest list looks like a collection of misfits – representing some of the most deep diving and wide ranging of offshore species alongside those that hug the coast so tightly they could easily benefit from legs:  Indo-Pacific common dolphins (Delphinus delphis tropicalis), common bottlenose dolphins (Tursiops truncatus), spinner dolphins (Stenella longirostris), Indo-Pacific bottlenose dolphins ( Tursiops aduncus), rough-toothed dolphins (Steno bredanensis), Indian Ocean humpback dolphins (Sousa plumbea), Risso’s dolphins (Grampus griseus), false killer whales ( Pseudorca crassidens), killer whales ( Orcinus orca), dwarf sperm whales (Kogia sima), melon-headed whales (Peponocephala electra), short-finned pilot whales (Globicephala macrorynchus), Cuvier’s beaked whales (Ziphius cavirostris), sperm whales(Physeter macrocephalus), Bryde’s whales (Balaenoptera edeni), Arabian Sea humpback whales (Megaptera novaeangliae)and blue whales ( Balaenoptera musculus cf indica).

Evidence from 17 years of work at this site has recently been compiled to nominate the study site as a candidate for one of the world’s most ‘Important Marine Mammal Areas’ (IMMA). This was proposed at a workshop organised by the IUCN Marine Mammal  Protected Area Task Force in March 2019 in Salalah, Oman.  Self-promoting, the site ticks almost every criterion in the book for what is required to define an important area for whales and dolphins, from the high diversity of species to its quirky isolated and endangered residents. One of these residents, ‘Quasimodo’ a particularly hump-backed female Arabian Sea humpback whale with a spinal abnormality made a sneak appearance as a few members of the task force team passed through the site in mid-March on their way out of the IMMA workshop.

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Quasimodo, a particularly ‘humped’ humpback whale, photographed in Dhofar in 2011.  Courtesy of the Environment Society of Oman.

The high diversity of cetaceans with both coastal and offshore habitat preferences is thought to be related to the unique bathymetric and oceanographic conditions. The coastline on one side of Hasik is characterised by a mountain escarpment which plummets down to the continental slope offshore, whilst to the other side is a large shallow embayment of continental shelf. The interface between these seafloor features generates strong, sustained currents that promote year round pulsing of upwelling nutrient-rich waters from the deep ocean. With the onset of the southwest Indian Monsoon during the summer months, the upwelling along the southern coast of Oman is amplified, transforming the space from a sub-tropical to a temperate oceanic regime. Only accessible to the research team outside of this turbulent season the humpback whales have been observed consistently in the area every winter and spring. Singing (related to breeding) is the popular pastime of a group of approximately six male humpbacks that are consistently re-encountered at the site year on year. More unconventional activities have also been observed, such as switching between competitive breeding related behaviour and ‘bubble-net’ feeding just breaths apart. Such habitat use is considered a unique trait of this non-migratory population where social and dining engagements can all be serviced in the same time and space. Humpback whale populations in all other parts of the world typically have such delights separated by months of travel and thousands of kilometres as they migrate between polar feeding areas and tropical breeding grounds.

Dhofar map with sightings

The coastline on one side of the Hallaniyats Bay is characterised by a mountain escarpment which plummets down to the continental slope offshore, whilst to the other side is a large shallow embayment of continental shelf. This figure shows that unique bathymetry and the species encountered in the Hallaniyats Bay region, southern Oman between March 2018 and April 2019 (courtesy of Five Oceans Environmental Services).

The presence of a smaller lesser known baleen whale, the Bryde’s whale, has also been documented on almost every survey in the area. This species seems to specialise in taunting the research team. During the last survey, Bryde’s whales pulled off their best trick by breaching in front of the teams’ campsite on a number of occasions and then running off to hide (although we eventually managed to catch up with them). As much as a mystery as the blue whales, this tropical whale is notoriously difficult to study due to its stealthy speed and preference for surfacing just where the research boat isn’t. As such it lies high on the list of miscreants for the research team to investigate.

Blue whales are infrequently observed in Oman and were documented off the survey site for the first time in 2011. Their presence elsewhere in the northern Indian Ocean (e.g. off Sri Lanka) is better known, although the taxonomy and population structure remains unresolved. Echoing the Arabian Sea humpback whale enigma, the jury is out on the details of their population affinity and range. Are they unique and isolated to the NIO or are they part of a larger more wide-ranging population in the Indian Ocean? Recent literature cites blue whales found in the NIO as either a subspecies of a smaller form of blue whale known as pygmy blue whales found across Indian and Pacific Oceans (Balaenoptera musculus brevicauda – Ichihara, 1966), or, intriguingly as another unique whale, the Indian Ocean blue whale (Balaenoptera musculus indica – Blythe, 1859). The ‘indica’ sub-species designation identifies the taxonomy of this smaller form of blue whale with a more restricted geographical range, not dissimilar to the Arabian Sea humpback. Efforts to resolve this impasse on population affinity and range have so far been painstaking. To approve the ‘indica’ form the evidence needs to demonstrate geographical isolation and significant biological differences. This is where the story slides from blue to grey.

To date only two genetic samples have been processed from blue whales in the NIO and the results demonstrated no discernible difference in the DNA sequence between pygmy blues found in the southern Indian Ocean and their counter-parts to the north. However, the sample size was considered too small to draw reliable conclusions. Study of historical whaling data shows that blue whales encountered in the NIO are 0.5m shorter than southern blues; a relatively small difference. However, the cookie cutter shark bites observed by whalers on blue whales taken in the southern Indian Ocean have not been observed on blues to the north of the equator. Whalers have also described a gap in the central Indian Ocean where very few blue whales were ever observed, suggesting there may be no movement north and south across the equator. With song often used as a descriptor for placing geographical limits on the population structure the ‘isolationist’ theory is further supported by the unique song or call types recorded off Sri Lanka and the Chagos Archipelago but never further south in the Indian Ocean. Meanwhile, sightings and strandings data show blue whales to be present in the Indian Ocean year-round. Recent re-evaluation of whaling records has revealed no discernible seasonality to  the reproduction of blue whales in the NIO, where-as the breeding season of blues in the SIO is understood to occur only in the austral winter.

Last year a new twist emerged with the Oman team reporting to the IWC Scientific Committee a completely new baleen whale song type. The song was recorded in 2012 at the Hasik study site with call attributes that imply the source of the ‘baritone’ vocalisation was most likely from a blue whale.

With that as background, it’s no wonder that we were reeling with expectation as we bounced our way towards a sighting called-in by the shore-based team on day three of our survey in April. This was the latest in the season we had been on survey at the site for many years. Multiple tall blows could be seen from the boat through the building Force 5 seas with momentary glimpses of a broad back that slowly transformed into the unmistakable mottled steel grey blue of a blue whale, rolling into a dive. Thinking we were in for a brief sunset encounter with a transiting ‘5 O’clock whale’ the team moved into position to collect photo-ID data before being left trailing in a pool of bright orange faeces as the whale dove out of site with its tail high in the air. The fluking behaviour is not considered a common behaviour of blue whales, but is well documented off the coast of Sri Lanka on feeding aggregation sites. However, the bright orange faeces was certainly a sign of recent feeding and the team bagged a sample followed by a well-timed biopsy on the next surfacing of the animal. Over the following 2 days we documented at least another four animals performing regular dives with a couple of minutes surface time followed by 10-14 minute dive time intervals. The whales ranged in length between 12m and at least 18m. In total five biopsies and two separate faeces samples were gathered, together with a collection of 100’s of photos for ID use. The biopsy samples are the first to have been taken from live blue whales in Oman: the two previous DNA samples came from stranded whales. The results are accompanied by referenced photo-ID images of the biopsy takes.

Blue whale dive sequence

As before this special corner of the Indian Ocean has produced the unexpected. The game is now on to get the biopsy and faeces samples sequenced and photos processed to ready them for comparison with other catalogues in the Indian Ocean. 2019 could be the year we get closer to unravelling the mystery of blue whales in this part of the northern Indian Ocean. Or will these investigations just throw up yet more questions? Which-ever way this pans out the team is aware there is far more work to be done to help understand, and ultimately safeguard, this important corner of our blue planet.