An Arabian Sea humpback whale, which usually hugs the coastline of Oman, has been tracked making a journey to Goa in search of food or a mate.
It is the first direct evidence of the species crossing the Arabian Sea, and is considered by scientists to be a behavioural anomaly because they are so uniquely adapted to their habitat.
Around 80 of the whales live in the waters off Oman and are classified as endangered. It was thought to be the only humpback whale population that does not undertake seasonal migration.
After years of tracking by researchers, one female has defied that theory.
Arabian Sea humpback whales diverged from southern hemisphere humpback whale populations around 70,000 years ago, adapting to their environment and radically changing their foraging strategy by staying in one place.
The study monitored whales’ dives using 14 satellite tags deployed at Hallaniyat Bay, a marine sanctuary about 50km off the Omani coast and the Gulf of Masirah on Oman’s eastern coast. They transmitted for 53 days on average, sending more than 1,800 locations for all tagged whales.
Tagging
Dr Andrew Willson, a marine scientist and founding director of Future Seas Global SPC, said the latest development “fundamentally challenges our understanding of humpback ecology”.
“Up to this point there was no direct evidence of whales moving the long distances across the ocean basin,” he told The National.
“The first sets of tags hadn’t shown much more than localised movements off the coast of Oman. So when this whale started moving away from the coast and out into the open ocean it was very exciting. We had no way of knowing where she was going to go … but our hope was that the movements would reveal other suitable habitat and potential hotspots in the region that could be investigated further.”
The results were published in Frontiers in Marine Science. He wrote in the journal: “We show ASHWs [Arabian Sea humpback whales] predominantly stayed within a very restricted home range along the coast of Oman.
“Alongside very localised movements, we also document the first long-distance movement of an ASHW across the Arabian Sea, pointing to the possibility of other important habitats.”
He added: “We had so many questions about the daily life of the mysterious humpback whales found in the Arabian Sea, of which we would only get fleeting glimpses during long hot hours of boat surveys.
“Tagging these whales allowed us to peel back the lid of the sea and check in online to see where they were each day.”
Close to home
All six animals tagged in Hallaniyat Bay stayed within a 400km area. Due to monsoons, the western Arabian Sea is one of the most productive upwelling zones globally, where deep nutrient-rich water rises to the surface like an oceanic fertiliser, and can support whales year-round.
“We think the movements of the whales in our study relate to their tracking of inshore prey, likely sardines, over the continental shelf. Deeper dives off the continental shelf could be related to searching for other food found in deeper water, such as krill,” Mr Willson said.
However one female, whale known as Luban – named in Arabic for the frankincense-shaped pattern on her tail fluke – appeared to go rogue and travelled east, being detected off the west Indian state of Goa and remaining there for a month.
Luban covered around 7,000km on her return journey, before being spotted back in the Gulf of Masirah. It’s always a relief when we make resightings of these amazing whales given the limited size of the population,” said Mr Willson.
Humpback whales excellent navigators, so the researchers believe Luban’s journey which started and ended at the same point, was deliberate.
While humpback whale song has previously been connected between Omani and Indian coasts, her journey provided the first direct evidence of her species crossing the Arabian Sea.
The team believes that finding food or reproducing – key factors that motivate humpbacks to travel – lay behind her journey.
As there were only two females tagged, researchers now hope to discover if females move around more than males, or if the small size of the study means others have made a similar journey without being spotted.
Mr Willson told The National: “Arabian Sea humpback whales are unconventional in that they don’t do the long distance migrations. But we think it is high likely these movements are routine, it is just difficult to detect because the population is very small, and finding whales at sea to positively identify is hard. These studies are also expensive and hard to mobilise and get tags on to whales. It’s a complicated operation that takes significant time and resources to mobilise the fieldwork and process the data.”
Protection
The team hopes their work will help protect the small and isolated population of whales that’s facing impacts from climate change and human activity such as fishing.
“Coastal fishing communities in Oman have revered and respected these whales for many generations,” said Aida Al Jabri, a marine expert supporting the study with the Oman Environment Authority. “For rapidly modernising societies in this region the study puts these whales more into view. This is critical to supporting their conservation.”
Co-author Suaad Al Harthi, the executive director of the Environment Society of Oman, said: “The Arabian Sea provides unique conditions allowing a once-migratory species to completely change its ecology. It’s a testament to how extraordinary the region is. We hope their adaptability will help ASHWs in uncertain times when their domain is influenced by accelerated climate change.”
