Dolphin ID Project
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 2018
A total of 2500 Spinners (during 17 cruises at Kuda Huraa) and 450 Spinners (5 cruises at Landaa Giraavaru) were sighted, along with several small pods of Bottlenose dolphins and False killer whales. Dolphin calves were commonly seen, and the Spinners actively interacted with our boats on most of the excursions. The largest pod was an estimated 800 Spinners, whereas the smallest was a pod of 5 Bottlenose.
We were able to add 25 new Spinner dolphins into our ID database, and recorded one positive re-sighting (‘Amber’ from 22 April) bringing the total to 47 uniquely identified individuals.
Over the 13 dolphin cruises at Landaa this month, we recorded 480 Spinners (10 to 200 per pod) and 100 Bottlenose (4 to 40 per pod). This yielded the positive identification of two new Bottlenose dolphins, and the possible re-sightings of two Bottlenose and one Spinner.
At Kuda Huraa, we arranged 14 cruises and were able to record 1685 Spinners (20 to 250 per pod) but zero Bottlenose dolphins. We now have a total of 99 uniquely identified Spinner dolphins.
During August, we recorded 830 Spinner dolphins (Stenella longirostri) around Kuda Huraa, plus 250 Spinners and 33 Bottlenose dolphins at Landaa Giraavaru. This resulted in six Spinners and five Bottlenose being uniquely identified and newly added to our database, plus possible re-sightings of a further 12 individuals.
September was a good month for cetacean sightings, with encounters lasting 10-50 minutes and comprising:
– 2000 Spinner Dolphins (Stenella longirostri) in pods of 10-300, usually with calves,
– 22 Bottlenose Dolphins (1-10 individuals),
– 50 Pilot Whales.
34 new Spinner dolphins were successfully identified as unique individuals due to their characteristic fin shapes.
We also have successfully re-sighted over 40 individuals, including:
– ‘Becky’ – re-sighted three times in the past month, and
– ‘Snow’ – multiple re-sightings, and easy to ID due to a condition called leucism, the loss of skin pigmentation. (Not to be confused with albinism, the complete absence of pigmentation causing white skin and pink/red eyes).
At Kuda Huraa, we recorded 1870 Spinners in pods of 20-300 individuals, plus a single pod of 25 Bottlenose. Calves were sighted during all the trips.
A total of 21 new Spinner dolphins were uniquely identified and added to our Dolphin ID database, and we made successful re-sightings of two individuals.
At Landaa Giraavaru, we recorded 525 cetaceans, comprising:
– 475 Spinners (pods of 10-150 individuals),
– 9 Bottlenose,
– 10 Pilot whales,
– and amazingly, 22 Sperm whales near Reethi Beach!
A total of 3 new Bottlenose and 4 new Spinner dolphins were individually identified and added to our database, along with confirmed re-sightings of 1 Bottlenose and 7 individual Spinners.
At Kuda Huraa, 1280 Spinners were sighted in total, plus 1 pod of approximately 50 Short-fin pilot whales (Globicephala macrorhynchus) that were travelling with a pod of 100 Spinners. From our collection of photographs, we were able to uniquely identify 35 new Spinners and confirm 22 re-sightings.
At Landaa, 380 dolphins were recorded – 250 Spinners (in pods of 10 – 150 individuals) and 130 Bottlenose (10 – 60 individuals). 4 new Bottlenose and 3 new Spinners were uniquely identified, plus 1 Bottlenose was confirmed as a re-sighting.
At Kuda Huraa, 860 Spinners were recorded for the month, in pods of between 20 to 150 individuals, with encounters lasting from 21 to 41 minutes. From our photographs, 14 new Spinners were uniquely identified (current database total now 137 individuals) with a further 20 dolphins confirmed as resightings this month (now totalling 247).
At Landaa, we conducted 11 dolphin cruises plus one private excursion, with an estimated 778 dolphins recorded, comprising 755 Spinners (pods of 30 to 150 individuals) and 23 Bottlenose (pods of 3 to 20). From our photographs, we were able to uniquely identify 1 new Bottlenose, and confirm a resighting of 1 Spinner.
During 2018, we conducted a total of 175 dolphin cruises (82% success rate) at Landaa, recording a total of 6,800 Cetaceans (mostly Spinners, with frequent Bottlenose and occasional Pilot whales, Risso dolphins and Sperm whales).
Spinners (above) and Bottlenose (below)
Dolphin Diary 2019
At Landaa Giraavaru, we sighted 525 Spinner dolphins (in pods of 20 – 140 individuals) and 45 Bottlenose (15-30 individuals) across 9 dolphin cruises.
At Kuda Huraa, we recorded 905 Spinners (in pods of up to 200 individuals) and one pod of short-finned pilot whales across 16 dolphin cruises.
From the photographs we took on the excursions, we were unable to positively identify any new individuals, however 7 dolphins were confirmed as re-sightings.
At Landaa, we conducted 11 cruises during the month, and recorded an estimated 500 dolphins in total (30 Bottlenose and 470 Spinners).
At Kuda Huraa, we conducted 15 cruises and sighted 450 individual Spinners (pods of 3 to 70 individuals), during encounters that lasted from 9 to 41 minutes in duration.
No new individuals were uniquely identified, but we will keep the monthly photographs for future referencing.
‘Circle’ [SL135] re-sighting, January 2019
Dorsal fins for our database, February 2019
Spinner dolphin, close to Kuda Huraa, February 2019
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