‘River pits,’ caused by unregulated release of water from dams, pose threat to otters along Moyar River
Researchers say these ‘pits’ are formed when high water ow creates holes in rocks; otters, who get into these holes in search of food, can get trapped when the pumping of water for electricity is suddenly stopped
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The deaths of a group of Asian small-clawed otters (Aonyx cinereus), inside a “river pit” formed by high water ows from the Pykara Dam, has highlighted an often overlooked risk faced by river otters along the Moyar River due to the unregulated release and withholding of water from the district’s major dams.
The Asian small-clawed otter, classied as ‘vulnerable’ in the International Union for the Conservation of Nature’s Red List, is among two otter species found in the Moyar Valley, the other being the Smooth-coated otter (Lutrogale perspicillata).
The deaths of the three Asian small-clawed otters in a river pit, around eight kilometers from the Pykara Dam were observed by researchers, K. Narasimmarajan, H.S.Palei and M.T. Mathai and published in the IUCN Otter Specialist Group bulletin, titled “Do natural river pits pose a danger to otters? A eld report from the Moyar Valley,
Western Ghats, India.”
Describing a river pit in the bulletin, the researchers state, “River pits are formed naturally when high water ows crack rock surfaces and creates [sic] a deep hole, or pit, in the bed of the river, about 1 to 3 meters deep. These pits ll with water during a discharge from upstream hydroelectric dams, but dry up during the non-pumping time.”
The mortality report detailed in the bulletin showed that three of the otters had become trapped in the pit and were unable to escape when water levels dropped due to water release being stopped upstream in the Pykara Dam.
“From 1947-54, the Tamil Nadu Electricity Board (TNEB) constructed a dam in Pykara on the Moyar River, with a hydro-electric power generation capacity of 28 MW/day. Unregulated water pumping during electricity generation, controls the entire downstream river water ow, restricting the free movement of Small-clawed otters. Otters can become trapped in the deep river pits when the pumping of water is suddenly stopped. The otters cannot escape from the bottom of the pits when the water level falls too far below the surface level. Unregulated or sudden stoppage of water pumping from the dam can lead to death of a trapped otter due to starvation,” the authors note.
The researchers, apart from noting the death of the three otters in the river pit, also rescued a rat snake from within it, indicating that a number of species could be at risk from falling in and being unable to escape. “Asian small-clawed otters, having small paws, might face challenges climbing slippery surfaces like deep rocky pits,” the researchers note.
Speaking to The Hindu, K. Narasimmarajan, one of the authors of the paper and a PhD scholar at the Department of Zoology, Madras Christian College, said river pits attract food sources such as sh and crustaceans, which draw in the otters.
“This observation has highlighted the importance of regulating water ow and ensuring the regular, periodic release of water along river systems supporting endemic wildlife,” said Mr. Narasimmarajan.
He said the pumping of water needs to be regulated with the co-operation of the Tamil Nadu Generation and Distribution Corporation (TANGEDCO) and the Forest Department, with the Forest Department also being urged to conduct regular checks for wildlife stuck in these river pits to avoid fatalities.
The population of the Asian small clawed otter is believed to be around 400 individuals, while the Smooth-coated otter population is believed to be around 225 individuals in the Moyar River.
The low population numbers, combined with the understanding that the population of the two species is declining, necessitates ensuring that threats to the animals are minimised, said Mr. Narasimmarajan.