Below we hear from a good friend of WDCS, Dr Dipani Sutaria and her work on Irrawaddy dolphins in Chilika lagoon in India - enjoy!
The best days are when the water is calm and soft with a few ripples reflecting colours that come out to touch you. Sometimes, the softness is disrupted by a clown-like marine creature spitting a long spout of water almost at you – I first saw this creature in 2002 and till today, Irrawaddy dolphins simply amuse me. Their presence gives our study site a character far different from any place I have visited, as long as one has the patience to wait, experience and laugh!
Chilika lagoon is a beautiful brackish water lagoon along the southern coast of Orissa, India. When we speak to fishers living along Chilika shores, they tell us with a smile that Irrawaddy dolphins have been present in Chilika, ever since it was formed. Called ‘khera’ in the local language, the local populace considers these dolphins to be a blessing and a sign of fish presence. The late jejebapa (grandfather) of Naran babu, at the time a full ninety nine years old, told me “ Daughter, the day there are no dolphins in Chilika, there will be no fish, it is just not possible”. I used to keep a day in the week free from scientific inquiry and on that day, I would go across to the rajhans channel, and traverse the waters in a dug-out canoe with a young fisherboy. He used to call out to the dolphins “Kuu ku ku ku ku”…the dolphins would smoothly glide along with our canoe. This deep, knowing and almost spiritual connection that the fisher people of Chilika have with their dolphins is the most hopeful and beautiful part of ongoing conservation research here.
Memories of the first time I visited the field site on Holiday with Ranjeet Pattnaik in March 2002 are still vivid. We got our first record of A1 or scoopfin – one of our most coveted individual’s (and may she live long and pass her survival genes to many generations that follow). When the project started in 2004, with conservation objectives we needed to estimate population size, area of occurrence, home ranges and patterns in space use using boat surveys to put together a photo-ID catalogue of the dolphins. The first few weeks were depressing as we were not getting as many new fins as we wished, but slowly and steadily our catalogue grew and I still remember the joy every time we found a new dramatically shaped fin . I had to decide then if we should give them alpha numerical ID’s or actual nicknames and I chose the former much to my assistant’s discontent! In field there is a certain joy in not doing what everyone expects you would do…. we must allow ourselves some pleasures in a place where there is no dance, wine or chocolate and the electricity cut constantly challenges our sanity.
We managed to identify 80 individual dolphins using natural marks, one more beautiful than the next (pictures). The younger animals are difficult to identify as their fins have still not got tarnished and dashed. We used these data to estimate abundance of the population which is approximately 109 to112 individuals at CV=0.07 based on surveys from November 2004 to December 2006. We also found that the total Extent of Occurrence for Irrawaddy dolphins in Chilika was <330km2; and the Area of Occupancy was <131km2, both of which are less than half of the available habitat. The dolphins concentrate their use in two core areas in the Lagoon: the Outer Channel (12km2 ) and the South-Central Sector (49km2). The core areas appear to be the major feeding grounds for Irrawaddy dolphins in Chilika Lagoon, with feeding, milling and socializing dominating the day time activity budget. Interestingly, the site fidelity of individual dolphins is high with more than 80% of the individuals remaining within 10km of their mean centre. Some of the individuals showed large ranges, and we call them explorers while others stay within their small home ranges, and we call them stayers. We have shown below some of the individuals and their home ranges, to give you an idea of the space used.
These dolphins are striking in their habits. They exhibit various kinds of feeding strategies, solitarily and in groups of two - three to large groups of eight-nine animals. Feeding strategies include plume feeding, kerplunking, herding fish to shallow waters and then feeding sideways along the shores. The dolphins are also seen feeding from fixed shrimp and fish trap nets, which are used as barriers for dolphins to catch fish from. Another special kind of strategy used by Irrawaddy dolphins is that of ‘spitting’ We have observed that the spitting action is used to stun fish either from the bottom or from within the water column.
Long term behavioral studies in Chilika is a dream which I hope comes true. I now observe social behavior between individuals to assess the society and associations that exist between individuals. One of my recent exciting observations was that of herding behavior, which is common during the months of March to May, the probably breeding season for Irrawaddy dolphins in Chilika! Our work is greatly limited by not having access to genetic samples and thus not knowing the sex of the individuals we are observing. I hope that future work in Chilika is able to overcome such barriers.
The dolphins do not use the entire lagoon, which brings us to one of the major concerns-that of habitat quality and restoration. Shrinking of the lagoon has been a constant worry and the Chilika Development Authority uses maintenance dredging to maintain the lagoon ecosystem-they even opened a new mouth to the sea to maintain sea water flow.