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Decoding the Dangers to Dolphins
Posted on December 8, 2011
The Ganges River dolphin is the most evolutionary distinct of the three river dolphin species and extremely threatened. Nadia Richman is working on the effects of fisheries and pollution on this species in Bangladesh and India for her PhD with the ZSL and Bangor University.
After losing 15 hours of my life to queuing in visa offices, 72 hours to dysentery, and well over a week to religious festivals, my studies on the Ganges River dolphin in Bangladesh are finally underway. Like most freshwater cetaceans, the status of this species is poorly known, but it is probably the most threatened river dolphin species since the extinction of the Baji in 2007 . They face a number of threats including targeted killing for fishing bait and medicinal oil, boat strikes, pollutants, and loss of habitat due to wide-scale siltation of rivers and damming. With its 24,000 linear km of rivers (I am not surveying them all), Bangladesh is a major stronghold for the population.
I began the 5 month field season with a 10 day boat survey of the Western Sundarbans, which gave me the necessary experience to carry out my own boat survey in 4 months time and the opportunity to meet in-country collaborators. We confirmed a number of hotspots in the region for Ganges River dolphin as well as finless porpoise, the Irrawaddy dolphin and Indo-pacific Humpback dolphins……oh and pirates.
I am now back on the southern border of Bangladesh, where I have been interviewing riverine fishers for the last two weeks. Through a series of carefully-framed questions and some observational work, I hope to establish the following: the types of fishing gear dolphins are most likely to become entangled in; mortality hotspots; additional causes of mortality; and motivations for killing dolphins. Together with an estimate of the population present in the southern river, these data will hopefully give us a better idea of whether annual mortality levels are sustainable and particular areas where we might need to minimise mortalities.
From interview surveys for this species in other areas, my initial idea was that fisheries-related mortality is the biggest threat to this species. While it is early days, my own preliminary interviews suggest otherwise. Dolphins are rarely encountered in fishing gear but are frequently seen dead on the riverbank, with no obvious scars from fishing gear entanglement. Fishers in the region believe that pollution from a local paper mill may be responsible. Further investigation has revealed that this paper mill is releasing 1,000 cubic metres of untreated caustic acid waste into the river every day and has no waste water treatment facility.
I have set up a reporting network to notify me of any dead dolphins and obtain tissue samples to analyse for pollutants The network has already proven useful: last night I was informed of a dead dolphin from which I now have 10 teeth, some blubber and muscle. I have also concluded that one paper on the feeding ecology of the Ganges River Dolphin from 1974 was correct when it described the dolphin as smelling of excrement. Interviews with fishers have also revealed a belief that dolphins die because they get “too fat”, but my attempts to explain post-mortem bloating have been met with blank stares.
You may be questioning the validity of these interviews, given that the killing of a river dolphin incurs a 12 year prison sentence. The assurance that I am not working for the government and that interview data is confidential, along with comedy moments involving me and deep mud, however, have lead locals to give me details of the medicinal dolphin oil trade. The government’s lack of information dissemination also means that few people know that killing dolphins is illegal. Conservation in Bangladesh is still in its infancy, but I believe there is hope for the river dolphin. As one fisher said, “I would be sad to see it go. It is beautiful but it has a very funny face”.