Saturday, September 19, 2015

Orca Project In Sri Lanka – An Ongoing Study Of The World’s Most Dominant Predator In Sri Lankan Waters



Words by : Georgina Gemmell

  |     Marianne Taylor & Michaela Hanusova of Whale Watching with Geeth

An apex predator of the ocean and iconic star of the hit film Free Willy, orcas (or killer whales) are generally not considered a tropical species. Though widely thought to roam in only cold or temperate waters, orcas are in fact one of the most widely distributed mammals on earth (second only to us humans), occurring in all of the world’s oceans from the frigid waters of the poles right through to the tropics…including these very waters, here in Sri Lanka.
Very little is known about the orcas that are sighted off the island each year, with only a handful of annual encounters, many questions surround this secretive population. However, as more people take to the water to enjoy Sri Lanka’s rich whale watching offerings, the opportunity to encounter and photograph these enigmatic visitors also presents an opportunity to study them; and Orca Project Sri Lanka (OPSL), a pioneering citizen-science initiative, is currently doing just that.
The project is the joint initiative of myself (Georgina Gemmell), head of ecotourism for John Keells Chitral Jayatilake, and wildlife tourism champion Gehan de Silva Wijeyeratne. While the study is only in its infancy, through working alongside the public OPSL has already begun to unravel some of the most basic mysteries surrounding these elusive whales. In addition to keeping a sightings log, orca images submitted by the public are used as part of an on-going Photo ID study, to identify and ‘track’ orca individuals. Across the world, Photo ID is one of the most widely used methods to study orca populations. It has the benefit of being completely passive, allowing researchers to follow orcas’ lives without disturbing them. Though it is patient research, in time Photo ID could reveal population estimates, sex ratios, births, deaths, movements, ecotypes, insights into diet and much more. Individual orcas are distinguished using three methods, one is using the unique marks, scars and tears (nicks) found on the dorsal fin, another may be the shape and marks on the saddle patch (the light grey area shaped like a saddle on the orca’s back, at the base of the dorsal fin), and the third is using the characteristic white eye patch above and behind the orca’s eye. Here in Sri Lanka, the orcas’ saddle patches are too faint to be a reliable feature for ID, so only the dorsal fin and eye patch are used.
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Already, Orca Project Sri Lanka has revealed some interesting and globally significant discoveries about these enigmatic visitors. The ID catalogue currently holds 13 individuals, and has provided the first confirmation that some orca travel all around the island, being sighted in Kalpitya (in the northwest), Mirissa (in the south) and Trincomalee (in the northeast). It appears that some individuals do indeed return to the island each year, with sightings being highest between November to January and March to April, which coincide with the Blue and Sperm whale season for the south and north, suggesting that the orcas may be in the area to predate on these species. In our recent publication ‘Killer Whale Predation on Whales in Sri Lankan Waters’ (currently in press with the journal Aquatic Mammals), OPSL revealed that orcas prey on other whale species here in Sri Lanka. The publication gained international recognition and generated a lot of interest among the marine mammal scientific community. It describes three predation events that took place off Mirissa, including the globally rare event of orcas attacking Sperm whales. It also provides the first official confirmation that orcas prey on Mesoplodont beaked whales, a little-studied and rarely seen deep diving cetacean. The paper also presents strong circumstantial evidence that suggests orcas may be opportunistically preying on Blue whales while in Sri Lanka.
Even though the orca is generally considered a single species (Orcinus orca) research has shown that orcas occur in different eco , Whatypes (like races), genetically distinct from one another, and specializing in a certain type of prey. In some parts of the world, the Pacific Northwest and Antarctica for example, more than one ecotype occur in the same waters but do not interbreed. We do not yet know if eco types occur in Sri Lankan orcas, and while we know that they hunt other whales we don’t yet know if they take other kinds of prey as well. It is hoped that with the support of the public, this exciting project will continue to grow and reveal more about this little-studied population, laying a foundation for future studies, and continuing to contribute to the overall scientific knowledge available for this iconic, complex and fascinating species.
If you have seen orcas off Sri lanka and would like to contribute your sighting or images to the study, please contact us at georgina.wildoceans@gmail.com. All images will remain the copyright of the photographer, and all credit for the sighting remains that of the observer.