[In January 2003 I accompanied an expedition that was conducting a survey of river dolphins on a stretch of the Mekong River in Cambodia. The expedition was led by Isabel Beasley, who was then a PhD student specializing on Orcaella brevirostris: also known as the ‘Irrawaddy Dolphin’ this species is found in many Asian river systems and deltas. The journal I kept during the expedition will appear on this site as a continuous series of posts. This is part 6 of the series.]
The dolphin pools have very distinctive shapes and the dolphins seem to dislike certain kinds of underwater topography. Isabel and her associates take regular soundings of the river bottom, with a hand-held sounding device. A detailed topographical survey of the Mekong has also been conducted recently and she uses that in building a comprehensive picture of the riverbed and the kind of underwater terrain favoured by the dolphin.
Generally speaking she finds that the dolphins don’t like very deep passages. There are areas that plunge to seventy metres, but the dolphins stay away from those stretches. They prefer pool shaped areas that are from 10 metres to 30 metres deep. These areas are also generally pool-like in shape. Less than 10 metres they don’t seem to like although local people have told her that they’ve seen animals occasionally going really close to shore.
Since coming over to this pool we’ve had good luck and have seen several animals surfacing quite close up. But Isabel has not been able to get any really good shots. This is very frustrating for her. The animals generally surface once, twice, and then they disappear. If you haven’t caught them by the second shot you’ve missed your chance. Isabel counts herself lucky to get one good shot a day. Yesterday she got a good dorsal-fin shot of Rags – that made it a very good day. The day before she got a good shot of Clasico.