The country representative of the Wildlife Conservation Society (WCS), the organization that discovered the Sundarbans’ remarkable dolphin population, has said that as yet there have been no observed “short-term effects” on the health of the forest’s dolphins, from the December 9 oil spill.
In an email interview from the Sundarbans, Rubaiyat Mansur Mowgli, who is also the principal researcher of the Bangladesh Cetacean (scientific name of dolphins, whales and porpoises) Diversity Project, did not rule out long term effects caused by exposure to the oil or decline in prey.
The dedicated conservationist, who has spent long periods in the Sundarbans over the last twenty years, also said that there was “an almost four-fold increase in commercial vessel traffic through the three wildlife sanctuaries established for the protection of the dolphins between 2010 and 2011(Dhangmari, Chandpai, Dhudhmuki).”
That coincides with the shifting of the shipping route from Khulna to Dhaka due to excessive siltation on the earlier route.
“A member of our team arrived at the spill site 4.1 km downstream of Chandpai just before sunset on December 9th. He noted a thick carpet of oil on the water surface and that the oil was still leaking from the vessel. By the afternoon of the next day the oil had spread at least 20 km upstream to Mongla and at least 20 km downstream to Harintana. We also documented oil trails and clumps several kilometers upstream in small side channels between Chandpai and Harintana,” Mansur said of the WCS team’s first reaction to news of the spill.
“From a second boat, with which I approached the site on December 10th, we noted trails, patches, clumps, spots and sheens of oil between Mongla and Chandpai. Almost all floating objects, including clumps of water hyacinth, were covered on the bottom portion with a gooey residue. The same black residue could be seen on the pier pilings for at least a half meter in the falling tide,” he added.
Researchers from New York-based WCS, which has an ongoing dolphin conservation project in the Sundarbans, were the first to inform the world of the population of 6000 Irrawaddy dolphins living in the freshwater regions of the Sundarbans, and nearby in the Bay of Bengal in 2009. Till then the IUCN’s estimate for the number of dolphins in the Sundarbans was just 450.
Asked about the activity or visibility of dolphins compared to the normal for this time of year, Mansur said, “On December 10th large patches and trails of oil were concentrated at confluences and meanders due to the same hydraulic properties that make them hotspots of abundance for freshwater dolphins. We observed a single Ganges River dolphin surfacing in Chilla and then another two at Nondabala at the entrance to the Shela channel of the Chandpai Wildlife Sanctuary for Freshwater Dolphins. Both dolphins surfaced too far away to determine whether or not they were surfacing directly in a slick or oil trail.”
The cetacean specialist, who also works with the IUCN, went on to add, “No immediate short-term effects were noted on the health of the dolphins but problems may occur later from long-term exposure to the oil and/or from declines in their fish and crustacean prey. Our team is currently carrying out an ecological investigation, including fish and crustacean sampling and a dolphin survey. We’ll repeat this again in the coming months and will then be able to identify changes in the distribution of the dolphins.”
A final judgment on the effect of the spill on the dolphin population is probably best withheld till then.
According to Mansur, closing the entrances of small channels and creeks with fishing nets initiated by the Forest Department was a good response under the circumstances, as long as the nets are regularly changed.
Mansur also stressed the importance of closing off the route to commercial vehicles, regardless of such accidents.
“Even without collisions or spills, the pollution these vessels discharge can degrade habitat and reduce fish and crustacean recruitment. Also, their large wakes can erode shoreline features and fill in the deep pools where freshwater dolphins congregate; and the vessels can collide with freshwater dolphins resulting in fatal injuries.”
Sundarbans oil spill ‘No short-effect on health of dolphins’