Sighting of a Super Pod of Pan-tropical Spotted Dolphins off Chennai Coast

On 6th August 2016, while on a pelagic birdwatching trip off the coast of Chennai, we stumbled upon a huge pod of dolphins approximately about 22 kms from the coast. Initially we thought it could be a group of different species as we saw a lot of movement, and breaching dolphins jumping high up in the air at a distance. They kept moving fast with one or the other individual breaching every now and then. There were calves and adults, singles, pairs and big groups. Each jump was different – small, fast, low, high, half twist, full twist, flat fall, vertical, “suspended”, half-hearted etc. Looking into the water below one could see dolphins racing with the boat crossing from one side to another in top speed. Their skin were pale pink and mottled.

Based on the videos and photographs we confirmed that the marvel we had witnessed was none other than a super-pod of Stenella attenuata commonly known as Pan-tropical Spotted Dolphin.

Three to five dolphins were breaching at a time every 5-10 minutes, and we estimated that there were about 10-15 pods of 100 dolphins/pod. We stayed with them for about 90 minutes and figured that the size of the full group could be in the hundreds if not a thousand. Indo-Pacific humpback dolphins (Sousa chinensis) [sighted in a an earlier trip on 13-09-2014] and Spinner dolphins (Stenella longirostris) were not present during this trip.

The day was hot and it was around 36°C at about 12 noon. The dolphins were moving constantly while also showing this acrobatic and social behaviour. They seemed to be moving while locally milling (moving in different directions at a given location – such as here they were moving both in a south-east and north-westerly mode while on the move). It is unknown whether they were feeding or carrying out a daily local movement in relation to prey. The fishermen mentioned that sightings of dolphins were common and abundant in these waters. They confirmed the presence of schools of tuna below, yet for some reason they decided against casting nets. The first of the dolphins was sighted at around 12.40 p.m. and the spectacle went on till about 02.15 p.m., the approximate distance between the 2 points being around 5-6 kms. The wind speed was around 18 km/h in the direction of West/South-West at 12 noon. The depth of the sea around these points was in the range of 90-95 meters. The average atmospheric pressure was around 1002 mb and the humidity around 50%.

The pelagic birding team: Rama Neelamegam, Aravind Amirtharaj, Gnanaskandan K, R. D. Hemraj, Vivek Shanbhag, Ganeshwar, Sharath, Vinoba, Udayakumar Balasubramanian, Gautham Krishnan, Rags Raghavan, Hopeland, Sreekumar Chirukandoth, Chandrasekhar Sundaram, Dipu Karuthedathu & Subramanian Sankar.