Irrawaddy Dolphin is quite a sweet little dolphin, dont you all think? Sadly the snubfin dolphin scientifically identified as Orcaella brevirostris is listed as vulnerable. Species is native to Bangladesh; Brunei Darussalam; Cambodia; India; Indonesia; Lao Peoples Democratic Republic; Malaysia; Myanmar; Philippines; Singapore; Thailand and Viet Nam. Irrawaddy Dolphin while listed as vulnerable does have some pretty major threats associated with it. These range from the following; The estuarine and freshwater occurrence of this species makes it particularly vulnerable to threats from the human activities that occur in these environments. Threats include direct mortality from fisheries interactions (particularly gillnet entanglement), vessel strikes, and habitat loss and degradation (e.g. declining or altered freshwater flows due to dam and embankment construction, environmental contamination). Live captures for aquarium display also have been a conservation issue in some local areas. Irrawaddy dolphins have been hunted directly in the past, at least in the Mekong and Mahakam Rivers, but are revered by local people in many areas of Asia. Irrawaddy dolphins are caught accidentally in fishing nets in almost all areas where they have been studied. The most detailed information on bycatch comes from the Mekong River where, of 15 confirmed human-caused deaths 2001-2005, 13 (87%) were due to gillnet entanglement. Based on reports from local fishermen and the retrieval of eight carcasses along the Mahakam River between 1995 and 2005, researchers in (2007) documented 48 deaths, 66% of them from entanglement in large-mesh (10 –17.5 cm) gillnets. Mortality also has been recorded in drift gillnets targeting elasmobranchs in coastal waters of Bangladesh and bottom-set gillnets targeting crabs in Malampaya Sound. Fishermen in some areas report the dolphins are released if found still alive, but in the case of drowned animals, the oil may be used for medicinal purposes or the flesh eaten. There have been no systematic observer schemes in freshwater or coastal regions, but evidence of bycatch and increased use of gillnets is cause for concern (IWC 2000). Fishing with electricity is considered a dire threat to the Ayeyarwady subpopulation. Many dams have been proposed that are likely to degrade the channels inhabited by Irrawaddy dolphins in the Mekong River Basin. Of greatest concern are the large run-of-the-river dams (dams without a reservoir that generally preserve a relatively natural flow regime) proposed for the Mekong mainstem near Stung Treng and Sambor. Dam projects in Lao PDR, Cambodia and Viet Nam threaten not only dolphins but also fisheries and therefore human livelihoods. A recent report of a high dam planned for the headwaters of the Ayeyarwady River, Myanmar, in Myitsone just below the confluence of the Mali Hka and N’Mai Hka tributaries, provides reason for concern about its effects on the population of Irrawaddy dolphins downstream. Deforestation and gold, sand and gravel mining are causing major changes to the geomorphologic and hydraulic features of rivers and marine-appended lakes where Irrawaddy dolphins occur. Increased sedimentation resulting from deforestation in surrounding watersheds has resulted in declining water depths in Songkhla, Chilika and Semayang Lakes. The last of these water bodies is appended to the Mahakam River and previously supported dolphins throughout most of its breadth. Now it contains suitable habitat only in a small area near the channel connecting it with the mainstem. Between 1992 and 1997 the maximum depth of Chilika Lake declined from 3.4 to 1.4 meters and the accumulation of sediments led to shrinkage of the opening channel and a dramatic decline in salinity. A new channel dredged in the northern portion of the lake in 2000 apparently has mitigated at least some of the problems caused by sedimentation. Habitat loss and population fragmentation in several areas have resulted from the proliferation of fixed fishing gears. In the middle and southern portions of Songkhla Lake about 27,000 Sai nong or sitting traps and 13,000 Sang sai or barrier traps create more than 8000 linear km of barrier in multiple rows. These fishing structures are left in place year-round and restrict dolphin movements such that their habitat is substantially reduced and the potential for demographic interaction with individuals in the Gulf of Thailand is eliminated.
Posted on: Mon, 01 Dec 2014 02:21:01 +0000
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