Fish ladders and hatcheries planned for species threatened by hydro-power projects

Bhutan’s hydropower projects, the engine of the country’s economy, is affecting the ecosystem and migratory patterns of native fish stock. To mitigate the threats, the department of livestock has begun breeding program for native species like golden mahseer and snow trout. Studies conducted by the department has found that regulating the water flow using dams result in high mortality of fish eggs and younglings and also cause destruction to habitat and food source downstream. The threat Existence of a dam on a river results in the modification of the river’s physical, chemical and biological attributes and cause wide changes in the response of the fish and an overall change in the community structure of fish. The construction of dam breaks the continuity of the river and blocks the migratory route of fishes to their spawning habitats, and also affects the spawning sites downstream due to their operations. “Fish blocked from their spawning habitats may reabsorb their eggs. It is a concern regarding the persistence of the species,” said Livestock Officer Karma Tenzin. A single storied hatchery building near the dam would be used for incubation of eggs and rearing with adequate protection from direct sunlight. The hatchery would be equipped with all necessary equipments like hatching trays and rearing tanks. Hatching trays and rearing tanks would supply with adequate clean water from the dam’s reservoir through efficient plumbing. The hatchery floor and walls will be lined with marble or ceramic, and the ceilings provided with waterproof lining. After they fishlings attain a certain size at the artificial breeding center, they are released upstream. Fishways Fishway, a ‘ladder’ for enabling fish to pass around a fall or dam in a stream, would attract fish toward a collection site upstream. Fishes are expected to swim up the fishway into a pool which would have facility to haul fish in high numbers with minimum effort and transport in tank trucks to hatchery for breeding or to release upstream sites. A fishway with a trap will be more practical in Punatsangchu as there is lack of information on the swimming efficiency of native fish species found in the river. Bhutan is believed to have the least disturbed population of Golden Mahseer. Elsewhere around the world, this fish is under indiscriminate pressure from changing habitat and fishing leading to its population decline.