Dolphin ID Project – 2020
During our guest dolphin cruises, we have started to take photographs of the cetaceans we encounter, to use for identification purposes. We take as many photos as possible at each encounter, especially on the calm, clear days.
We use only high quality photographs (correct angle, sharpness, lighting) for the identification process, but we do keep the lower quality images of any marked fins to use for future comparisons. Re-sightings are recorded in an excel sheet and the photos added to the individual dolphin’s collection. Periodically, we look through our archive of old photos to look for possible matches and re-sightings, and to remove any poor quality or indistinguishable images.
Taking good ID shots can be challenging under the variable conditions onboard (sun’s position, choppy sea) and it’s often not possible to angle the shot perpendicular to the dolphin’s body (to see the full outline of the dorsal fin). On average, out of 100 photographs taken, only 30 are good for analysis.
We photograph close-ups of dolphin dorsal fins
to record and identify the unique patterns
The photographs of the dorsal fin are cropped and analysed using image-matching software (we are trialling ‘Darwin’ at Kuda Huraa and I3S ‘Interactive Individual Identification System’ at Landaa Giraavaru).
Dolphins can be identified individually based on the notches, scars and markings present on their dorsal fin. Small wounds are known to heal within months, while large wounds caused by predation attempts or human impacts tend to persist (Lockyer & Morris, 1990 [PDF]). As missing tissue does not regenerate, dorsal fin mutilations are permanent marks that can be used for identification purposes.
We have created photographic databases for each of the four most commonly sighted Cetacean species in Maldives:
Spinner dolphins (Stenella longirostri) are by far the most commonly encountered Cetacean species in Maldivian waters. They are usually observed in pods of 40 to 100 individuals, exhibiting active and social behaviours including playing in the wake behind the boat and showing off their acrobatic skills (jumping, spinning, porpoising and bow-riding). They are the only species to actually spin in the air whilst jumping.
Young calves (30-90cm length) are often seen swimming alongside their protective mothers, and on some occasions even practising their jumping and spinning skills. Spinner dolphins are difficult to identify individually as most have “clean” dorsal fins with a smooth outline, lacking any distinct markings.
Bottlenose dolphins (Tursiops truncates and T.aduncus) are larger than Spinners, and often have more identifiable scars. They live and travel in much smaller family groups (even individually). Bottlenose are the most common species globally, and they have more fat so they can live in colder waters. They are sometimes seen jumping from the water, but never spin.
There are 2 different species sighted in Maldives – the ‘Common Bottlenose’ (Tursiops truncates) and the ‘Indo-Pacific Bottlenose’ (Tursiops aduncus), both very similar in appearance and difficult to tell part (‘Common’ is larger and found worldwide).
Baby Spinner dolphin
False killer whales (Pseudorca crassidens) are sighted seasonally in the Maldives, and are not so common. They can reach around 6 metres in length, although cold water populations have more fat insulation making them larger and heavier. They are usually sighted in family groups of 10-20 members (occasionally in huge groups of 500+) and often have uniquely identifying scars.
The mother is head of the group (‘matrifocal’ family structure) compared to pilot whales where the father plays a more important role.
Short-finned pilot whales (Globiocephala macrorhynchus) are sighted in family groups of around 15-30 members, but they will often migrate larger distances in groups of 100+. Here in the Maldives, pilot whales are often seen travelling together with pods of dolphins. Their large size and fat insulation means they can live in colder waters, and they often have many scars which makes for easier identification of individuals.
They were named ‘pilot’ whales as they follow a leader, and sometimes if that leader becomes sick or disoriented, the whole pod can end up stranding on a beach.
False killer whales
Dolphin Diary 2020
At Kuda Huraa, during a total of 15 guest excursions, we recorded 325 Spinner dolphins swimming in pods of between 10-75 individuals in encounters lasting from 5-44 minutes. We were also lucky to sight a pod of 10 pilot whales this month.
At Landaa, 380 Spinners plus 10 Bottlenose dolphins were sighted during 12 excursions in encounters lasting from 1-45 minutes. 7 new Spinners were added to the database, and there was 1 confirmed resighting (Rudolph SL0015).
More ? > Dolphin Diary 2018-19
Cetacean Sightings Around the Maldives
Big thanks to our fellow Cetacean fans, for posting these rare and exciting sightings to social media for us all to enjoy ! 🙂
Manta rays were a consolation today, On the way to #HanifaruBay with @AveylaMaldives we encountered 2 massive #BlueWhales outside Hanifaru Reef. It was just incredible.#BaaAtoll #Maldives #bluewhale #whalewatching #whales #ocean #scubadiving pic.twitter.com/v7t72YNQfk— LiquidSaltDivers (@LiquidSdivers) November 11, 2018
A day with @liquidsaltdivers— LiquidSaltDivers (@LiquidSdivers) December 6, 2018
Repost from @jonschutte - Let's go for a dive! Just a casual day heading out on the boat for a few dives when guess what we saw? You'll have to watch to find out! 🎬💙🌊 #dharavandhoo #maldives #islandlife pic.twitter.com/pbdwySMVBl