During the last few months several contradictory facts have been surfacing about fish ladders. Fish Ladders are small elevated steps or passes made in dams, with water releases to enable fish to migrate in the upstream (or downstream) of the dam.
This upstream migration is a part of the reproductive cycle of many fish, like Hilsa and Mahseer in India.
A study in the United States, a country with comprehensive attention to impacts of dams on fish, has concluded that actual numbers of fish who make it to their spawning grounds above dams with fish passages is a small fraction of targeted goals of these facilitie. For example, for American shad (Incidentally, Hilsa is also a type of Shad) – an important species for commercial and recreational fisheries that sustained generations on the East coast of the US – on average about only 3% percent of the fish that pass the first fishway make it past the last dam with a fishway in these rivers. Another example is that species such as Atlantic sturgeon cannot pass fish ladders—so for certain species, fishways do not work at all. Thus, in these systems, effective up and down stream passage is not being provided for anadromous fish. The result is that these species are getting listed as endangered or threatened one by one. The study actually concludes that looking at the dismal success rate of fish ladders and hatchery based recovery programs, “Ecologically and economically significant species restoration is not possible without dam removals”. (International Rivers)
A spectacular film “End of the River” chronicles the impact of small hydropower dams on fish in Europe. The film says that water released from the fish ladders is not enough for the fish species to survive in the downstream. https://sandrp.wordpress.com/2013/03/16/the-end-of-the-river/)
At the same time, ecologically designed fish ladders do help the fish get across the impediment of dams in some cases. For example, a weir on River Elbe in Germany counted its Millionth migrating fish in January 2013, 3 years after it was built.(http://www.dw.de/german-fish-ladder-celebrates-millionth-user/a-16509927)
Lesson for India seems to be that, in keeping with our livelihood dependency on riverine fish and their ecological value:
- Dams should not be built in ecologically important regions with documented fish diversity like in Western Ghats, Eastern Himalayas, near river confluences and near estuaries.
- Existing dams, where feasible, should have fish ladders and passages designed for Indian species, these should be monitored by independent committees with local participation
- all small hydel projects should have functioning fish ladders and most importantly,
- ALL dams should release e-flows which exceed the flows needed for fish survival and migration. E-flows should be released through fish passages and not turbines. They should keep in mind the need for longitudinal and lateral connectivities.
- No in stream sand mining should be allowed. No diversion of water for sand mining should be allowed. Sand mining should only be done manually, use of machine should not be allowed.
Unfortunately, even India’s premier research institutes like CIFRI are recommending eflows which are insufficient for species like trouts to survive. Its not a coincidence that these recommendations are very convenient for the private dam developers who are funding these studies.
POST SCRIPT: Some related articles on SANDRP blog: