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.
“We really were surprised with the findings because, in general, the humpback dolphins in other places of the world — from South Africa up to almost the Indian coast — all the populations were very small compared with this one, we are talking about 200 individuals maximum in most of the estimations,” said Mr Díaz López, chief biologist and director of the BDRI, who co-authored the research paper.
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 dorsal fins that were damaged.
“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,” said Mr Grandcourt. “We actually had seen some dolphins that had been entangled in ropes as well. 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 currently appealing to private and corporate sponsors to help fund the project.
“What we are trying to do now is we want to carry on running the survey to improve estimates and also to work on other species and, really, 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,” said Mr Grandcourt.
Added Mr Lopez: “We are talking about one species that is rare, there are very few populations in the world because it has been clearly impacted by the human activities because of living so close to the shore in areas where humans 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 measurements because we found the threats, 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.”
Dolphins in the Arabian Gulf
During the research team’s days at sea, they came across the three most common species of dolphins found in Abu Dhabi’s water. Over 55 days, there were 54 encounters with Indian Ocean humpback dolphins (Sousa plumbea), 48 with Indo-Pacific bottlenose dolphins (Tursiops aduncus) and five with finless porpoises (Neophocaena phocaenoides).
Indian Ocean humpback dolphins (Sousa plumbea)
Red List category and criteria: data deficient
These dolphins are characterised by the conspicuous humps and elongated dorsal fins found on the backs of adults of the species. The dorsal fin of the humpback dolphin is to some degree curved. The pectoral fins are small and the tail flukes have a well-defined median notch. Adults can reach from 1.8 to 2.6 metres and weigh in the range of 100 to 139 kilograms. They typically live less than 3km from shore and in water less than 25 metres deep.
“They play a very important role in the marine ecosystem because they catch other species of fish, but in some way also facilitate the equilibrium of the full ecosystem,” said Bruno Díaz López, director of the Bottlenose Dolphin Research Institute.
Source: Bottlenose Dolphin Research Institute
Indo-Pacific bottlenose dolphin (Tursiops aduncus)
Red List category and criteria: data deficient
It is probably the most recognisable of all dolphin species, with its steel grey skin tone, triangular dorsal fin and long rostrum, and it is found along the coastline of Dubai and Abu Dhabi. It differs from the common bottlenose dolphin (Tursiops truncatus), showing smaller size, longer rostrum and ventral spotting. However, the Tursiops observed in the Gulf sometimes lack some of these characteristics, leaving the question open as to whether they represent a different subspecies or if both species occur. Bottlenose dolphins can be found in small groups of few individuals but also in big groups of up to 40 individuals. They often approach boats and dhows.
Source: UAE Dolphin Project
Finless porpoises (Neophocaena phocaenoides)
Red List Category and criteria: Vulnerable
Very little information is available worldwide on this species and taxonomy is still an issue. It is one of the most elusive dolphins and among the least studied cetaceans in the world, with a distribution ranging from China through to Thailand, India and the Arabian Gulf. Finless porpoises are notoriously difficult to identify due to the lack of a prominent dorsal fin and their small size. In the Gulf they are a uniform dark-grey colour. They are coastal species that favour sandy and marsh areas and can be found in very shallow waters. These elusive animals have only been recorded a handful of times in this region and are usually only confirmed when they get stranded. Being coastal, this species has been critically impacted by human activity and habitat destruction.
Source: UAE Dolphin Project