World’s largest population of Indian Ocean humpback dolphins found in Abu Dhabi


The emirate’s shallow, warm seawater has attracted the world’s largest observed population of Indian Ocean humpback dolphins.

The Sousa plumbea population was identified during a marine survey of small cetaceans by the Environment Agency — Abu Dhabi (EAD) in collaboration with the Bottlenose Dolphin Research Institute (BDRI) along the coastal waters of Abu Dhabi in 2014 and 2015. Findings from the research project, which is ongoing, were published last month in the Journal of the Marine Biological Association of the United Kingdom.

“We are very excited to have identified the presence of the world’s largest population of Indian Ocean humpback dolphins in Abu Dhabi’s waters,” said Dr Shaikha Al Dhaheri, EAD’s executive director — terrestrial and marine biodiversity sector. “This demonstrates the international value of Abu Dhabi’s marine biodiversity and it is our responsibility to ensure the conservation of this important resource.”

Identified by a distinctive hump, elongated dorsal fin and small pectoral fins, the Indian Ocean humpback dolphin can grow up to about 2.5 meters and weigh between 100 and 139 kilograms. The species occur exclusively in the near-shore waters of the Indian Ocean from South Africa to the Bay of Bengal, usually living within 3 kilometres from shore in water less than 25 metres deep. But, little is known about the species, said Bruno Díaz López, director of the BDRI, who co-authored the research paper.

“Up until a few years ago, they were considered data deficient because there were no data about these species,” said Mr Díaz López. “Now this is the first time that there is an abundance estimation and it’s the biggest study about this species.”

The researchers spent 55 days over a period of five months zigzagging the sea along Abu Dhabi’s coast collecting data using hand-held GPS, binoculars, digital cameras and an iPad application used to collect and visualise the environment and human activity information. They applied a “mark-recapture” method, which involved taking photographs of the dolphins’ dorsal fins and storing the images in a digital database that could be used to cross-check future sightings.

“The dorsal fins have unique markings of patterns of notches and cuts that enable us to identify the animal if it is seen again,” said Edwin Mark Grandcourt, the study’s co-author and section manager — marine assessment and conservation terrestrial and marine biodiversity at EAD.

“In the same way that our fingerprints are unique to an individual, the dorsal fin of the dolphin is unique to that animal and we digitise the profile of the dorsal fin to then catalogue it. And then every time we make a sighting, we compare the sighted animals to our catalogue and it’s kind of like image recognition — similar to what a detective will use when he’s looking for a criminal. He will compare a fingerprint to a database — we will do the same thing, we’ll compare a dorsal fin profile to a database of profiles of dorsal fins and that will pull up the ones we have already seen before.”

The scientists spotted humpback dolphins on 32 of the 55 days they spent at sea, or 58 per cent of the time. They observed 54 independent groups of Indian Ocean humpback dolphins, ranging in size from one to 24 individuals. Most groups — 79 per cent — contained less than 10 dolphins. More than one-quarter of the humpback dolphins observed in groups — 27 per cent — were calves.

Using statistical inference models, the researchers estimate that there are 701 Indian Ocean humpback dolphins inhabiting Abu Dhabi waters.

Read more: originally published on August 8th, 2017. 


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