Abu Dhabi coast plays host to Sousa plumbea
Scientists surprised at presence of about 700 of the little-known but distinctive species
The shallow, warm seawater around Abu Dhabi emirate 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 in collaboration with the Bottlenose Dolphin Research Institute in waters off Abu Dhabi in 2014 and 2015.
Findings from the research project, which is continuing, 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, executive director of the agency’s 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.”
With a distinctive hump, elongated dorsal fin and small pectoral fins, the Indian Ocean humpback dolphin can grow up to about 2.5 metres and weigh between 100 and 139 kilograms.
The species exclusively inhabits inshore waters of the Indian Ocean, from South Africa to the Bay of Bengal, usually living within 3 kilometres of land in water less than 25 metres deep.
But little is known about the species, said Bruno Diaz Lopez, director of the institute, who co-wrote the research paper.
“Up until a few years ago, they were considered data deficient,” said Mr Diaz Lopez. “This is the first time there is an abundance estimation and it’s the biggest study about this species.”
The researchers spent 55 days over five months zigzagging the sea along Abu Dhabi’s coast collecting data using hand-held GPS devices, binoculars, digital cameras and an iPad application used to collect and visualise information on the environment and human activity.
They applied a “mark-recapture” method, which involved taking photos of the dolphins’ dorsal fins and storing the images in a database that can be used to cross-check future sightings.
“The dorsal fins have unique markings – patterns of notches and cuts – that enable us to identify the animal if it is seen again,” said Edwin Grandcourt, the study’s co-author and the environmental agency’s section manager for marine assessment and conservation.
“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.
“Then every time we make a sighting, we compare the sighted animals with our catalogue and it’s 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 compare a dorsal fin profile to a database of profiles.”
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 humpbacks, ranging in size from one to 24 individuals.
Most groups (79 per cent) contained fewer than 10 dolphins.
More than a 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 in Abu Dhabi waters.
“We really were surprised
The sightings also showed evidence of threats to the animals caused by human activities
with the findings because in general, the humpback dolphin populations in other places, from South Africa up to almost the Indian coast, were very small compared with this one – about 200 individuals maximum in most of the estimations,” said Mr Diaz Lopez.
The sightings also showed clear evidence of threats to the animals caused by human activity. Of the humpback dolphins that were identified, 12 per cent had damaged dorsal fins.
“There were a very high number of animals that had evidence of scars that resembled the cuts from propellers or scars that resembled entanglement in gear,” Mr Grandcourt said.
“We had seen some dolphins that had been entangled in ropes.
“They occur in an area where there is a lot of activity – dredging, shipping, fishing activity – so they are really threatened by those activities and that’s really evident from the number of animals that had scars.”
The research team is appealing to private and corporate sponsors to help with funds.
“What we are trying to do now is to carry on running the survey to improve estimates and also to work on other species,” Mr Grandcourt said.
“And to do that we have to reach out to the corporate sector and maybe people who want to spend on corporate social responsibility, or other conservation organisations who want to support us.
Mr Diaz Lopez said: “We are talking about one species that is rare. There are very few populations in the world because it has been clearly affected by human activities because of living so close to the shore in areas where human beings live. In five years, 10 years maybe, they can disappear.
“It is very important to see the evolution now. We need to monitor their presence in these waters because it is important for us to know if they are OK or if it is necessary to apply some conservation measures.
“We know that the main threats are marine traffic and fisheries, but we don’t know at what scale it’s affecting the population.
“Maybe the population is OK, and it will be stable over the years, but maybe not. So that is fundamental to know.”