Where are the fish ladders in our dams?

Fizala Tayebulla

Migration in fish population is a common phenomenon among several species for different purposes in their life cycle. Popularly talked about migratory fish species in India are Hilsa (Tenualosa ilisha), Pangas (Pangasius pangasius), Anguillid eels (Anguilla bengalensis, A. bicolor) as well as the Indian major carps (Catla, Rohu and Mrigal), because of their current ‘commercially extinct’ status in most upstream stretches of Gangetic and peninsular Indian rivers (ATREE, 2017). A similar discourse of endangering fish population due to anthropogenic causes in the river can be revealed for over 1000 species of fish that support inland fisheries in India. In ecology, a robust riverine fish population can be seen as an indicator of a healthy, functioning river. However, the likely reality in India is that the immediate word one might think of after ‘River’ is DAM more than say…fish. There are 4877 completed large dams and 313 large dams under construction according to National Register of Large Dams (NRLD) prepared by Central Water Commission (CWC).

Migration is a life process in fishes which happen for a simple reason that not all needs of a population (e.g. foraging, protection, breeding) can be fulfilled by a single habitat. As a result, many fishes have evolved a coordinated movement from one habitat to an alternate habitat throughout their life cycle, which is known to us as ‘migration’. The distance of migration movement can range from hundreds of metres to thousands of kilometres which is contingent to seasonality. The several classifications of fish migration can be broken down into three groups based on their relation to seawater/freshwater boundary. Oceanodromous migration occurs entirely within seawater, Potamodromous migration occurs entirely within freshwater i.e. in lakes, rivers, streams, or can be a combination of lake and fluvial bodies. Furthermore, migration cross seawater/freshwater boundary are diadromous, which branch out to three more categories:

  • Anadromy- born in freshwater, feeding and growth of fish in saltwater and returns into freshwater to reproduce. Eg, Pacific Salmon, Smelt, Striped Bass, Gulf Sturgeon.
  • Catadromy- born in salt water, spends most of the juvenile to the adult stage in freshwater and returns into seawater to spawn. Eg. Eel, Inanga.
Diadromous Fish Migration (Illustration Credit: Author)

  • Amphidromy- born in freshwater/estuaries but drifts into the ocean as larvae before migrating back into freshwater where most of growth and spawning occurs. Eg. Bigmouth Sleeper, Mountain Mullet, River Goby.

Construction of dams, barrages and weirs restrict the movement of fish species (like S. richardsonii, S. progastus, Tor tor etc) which move upstream to reach the breeding ground in order to reproduce. Dams tend to inundate sites which have sandy/gravel bed, shallow depth, low currents- such parts of a water body serve as a spawning ground for fishes. Blockading flowing water by concrete construction results in stagnation which leads to alteration of thermal stratification of water and its chemical composition, which in turn causes disturbance to trophic structures in the ecosystem. As the natural flow of downstream is altered, young migratory fish and refuge seeking fish descending to the lower reaches are thwarted, thereby facing threat to their survival. (CIFRI, 2008)

Incidents of biodiversity loss due to dam construction in India has not been uncommon. Post-impoundment, the count of fish species has thinned in most cases such as Hirakud (1957) on Mahanadi from 103 species to 40 (Job et al, 1955). There has been an overwhelming reduction of fish species in upstream of Indian dams. For instance, species like Mahseers and schizothoracines which travel up to 150 km upstream of Beas dam now suffer extensively especially in the Himalayan regions of the Beas river.

According to the current trends of development practices undertaken by the Government, it appears that India views development in hydro-energy as the key to address problems of population pressure (demand, employment opportunity, facilitate agriculture), caters to economic growth and energy needs. India’s outlook to development- damming rivers, estuaries and tributaries is a dominant national programme. From the point of view that the country’s water availability is poor, the Environment Ministry has proposed Indian Rivers Inter-link project (National River Linking Project) where thirty major rivers in the country will be linked through reservoirs and canals to reduce flood problems, generate hydropower and make water accessible to parched areas. Although there have been some plans/measures of facilitating fish migration (e.g. fish ladders), their success has been particularly insignificant. According to a 2010 report by the Central Inland Fisheries Research Institute (CIFRI), “Severe and drastic changes in the entire hydrological cycle of the river by dams and water abstractions has affected recruitment of most species … Larger dams are a major cause of degradation of aquatic environment and disruption of livelihood communities dependent upon the fishery along the rivers. In India, the natural flow of all major rivers has been regulated for fulfilling water demands of agriculture and the power sector, without giving any attention to the fisheries sector. As a result, rivers have lost their character and fisheries have suffered huge losses.” (Dandekar, 2012).

Amidst such a background, I came across an online article on World Fisheries Day, where a snippet of observing a working fish ladder in Columbia River, USA was cited. The narrative describes a chamber below the riverbed where fishes were witnessed using the fish ladder, where the documenter enthusiastically cheered the ‘fish hikers’ to cross the hurdle i.e. the dam (Himanshu Thakkar, 2016)

Brief history and trajectory of fish pass in India

Fish pass facilities have been part of Indian developmental processes since as early as 1873, spearheaded by colonizers of the time. Punjab in the early 1900s issued a bulletin on fish ladders and issued a call for improved fish passes. These propositions took shape in weirs constructed on river Sutlej, river Ravi, river Jhelum and river Chenab (refer to Fig 4). However, it is unfortunate that concentrated efforts towards enabling the process of fish migration after independence have dwindled on Indian rivers. The fish lock in Farakka Barrage on the Ganga in Bengal was put in place to help migration of hilsa. The tales of its successes become uncertain when (according to online report) officials and engineers working at the barrage tell reporters that there is no information or knowledge of any such fish lock on site. Furthermore, fish-pass in Narora Barrage on Ganga nor in Hirakud dam are functional, where one expects to see a flowing stream of water designed as a fish-pass, is a narrow lane of trickle flowing down. This miscarry is pinned to a design flaw of the pass being too slim for intended fish species to use, and the story ends there (Himanshu Thakkar, 2016).

Screenshot 2017-10-09 16.42.13
Figure 4. Fish ladder records in Punjab in the early 1900s (Source: CIFRI, 2008)

Designing fish passes, fish locks, fish lifts, fish ramp, slot passes entail channelizing fish movement in a small part of the dam for migration instead of their natural behaviour of utilizing the unabridged width of the river for the same purpose. The placement of a pass is therefore critical. The general yardsticks should be to meet biological requirements and the behaviour of migrating fish species.

India has clearly failed to keep pace with the rest of the world, where on one hand, other countries are decommissioning dams (1000+ dams in the USA over two decades) and other obstructions to protect riverine ecology and fish while India continues to have no successful (or operational) fish pass facility in any of the rivers. Such a lag cannot be bridged overnight, the setback is not due to the lack of infrastructure/facilities but the lack of consideration. From a summary of points made at National Consultation and panel discussion on ‘Linking Rivers, Barrages and Fish Migration’, several suggestions under a platter of assorted leitmotifs.

The field of Ecohydrology (an interdisciplinary study of interfaces concerning water and ecosystem) is a rather understudied area in India. As a result of which there is scarcity in the repertoire of data on impacts on stream ecology by anthropogenic activities and effects of human intervention on riverine fish. The panel stresses on the need of a national database on e-flows, optimum water release, nutrient flow should be prepared with respect to dam operation and an archive of information pertaining to fish migration, studying relations between e-flow and migratory species of fish, life history, traits and so on, so as to be able to design and develop species- explicit fish ladders and passes in regional frameworks. Such studies can be applied in the real world only with social awareness among general populous and fishing communities about native fish behaviour, migration and the need for conservation. Furthermore, the requirement for policy backup by the Government is of utmost relevance to undertake a critical assessment of river interlinking and dam operations so as to foster an approach in tandem with river conservation. Environmental Impact Assessments must take into account and appraise projects considering biotic, ecological and social impacts.

The matter of facilitating fish passes and ladders goes beyond the black-and-white development vs nature debate, it is a simple understanding that fish is a vital node in a riverine ecosystem and the health of a water body is subject to it. With the current ingress of new dams (313 large dams under construction) and similar infrastructure in rivers, thoughtful consideration of incorporation of fish migration facility in dams is quintessential for the sincere development of the country.


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