Study Shows 74% of SL’s Freshwater Fish Endangered
By Thameenah Razeek
Observing fish in their natural habitat can be both magical and relaxing. Each of these creatures, from the smallest guppy, to the largest whale shark have unique characteristics. Most people, unfortunately, believe that fish are only useful when they are dead and on a plate. Fish, in fact, are vital in ways that humans do not fully comprehend.
To begin with, they are critical to environmental diversity. Fish, whether caught in freshwater or at sea, provide food and nutrients to bottom-level animals that support the ecosystem. The Environment Ministry’s Biodiversity Secretariat assessed the threat status of Sri Lanka’s freshwater fish in 2020 a week ago to prepare the National Red List of Sri Lanka, which found that 74 per cent, or nearly three quarters, of the freshwater fish endemic to Sri Lanka are threatened with extinction.
Based on the distribution patterns of freshwater fish species, it was found that four major ichthyological provinces have been established in Sri Lanka: the Southwestern Province, Mahaweli Province, Transition Province, and Dry Zone Province. The Southwestern ichthyological province is home to the most endemic and vulnerable freshwater fish species.
The Mahaweli Province, which is primarily the Mahaweli River’s drainage basin, has the second highest number of vulnerable and endemic freshwater fish species. In the Dry Zone and Transition Zone Provinces, freshwater species assemblages are also abundant. These two provinces, however, may only contain the more common endemic species and a few vulnerable species.
The fish in the Dry Zone Province have a stronger affinity for the freshwater species of the Indian Peninsula. Because the vast majority of Sri Lanka’s freshwater fish live outside protected areas, they are directly impacted by all of the primary drivers of biodiversity loss, such as habitat loss and degradation, overfishing, pollution, invasive alien species, and climate change. Sri Lanka has a diverse network of freshwater habitats that includes both natural and man-made ecosystems. There are a total of 103 river basins that form a dendritic pattern and span the entire island.
The major rivers are estimated to be 4,500 kilometres long. In addition to rivers and streams, Sri Lanka has a variety of freshwater environments, including tanks, flood plains, pools, villus, and paddy fields.
According to Director of the Biodiversity Secretariat R.H.M.P. Abeykoon, many of Sri Lanka’s endemic freshwater fish are found in the Southwestern part of the island, where human population density is high, and the rivers in which these fish are found flow mostly outside protected areas. She claimed that deforestation, massive agrochemical surface runoff, toxic effluent release, gem mining, and the development of large and small hydropower projects are all threats to these indigenous freshwater species.
“Since the last National Red List, freshwater fish have gone through multiple taxonomic revisions, new species have been discovered, and many taxonomic uncertainties have been resolved. Hence, both the total number of species and the number of endemics to Sri Lanka have changed dramatically.
The IUCN’s Global Red List, on the other hand, had not adapted to these changes,” she emphasised. Director Abeykoon mentioned that 97 freshwater fish species were assessed using IUCN Red List categories and criteria, and each was assigned a threat status, and that the Biodiversity Secretariat (BDS) is in charge of assessing, monitoring, and revising the National Red List, with ongoing assistance from various panels of species experts.
A total of 61 endemic freshwater fish species were evaluated, with 12 endemic species designated as Critically Endangered (CR), 24 rangerestricted species designated as Endangered (EN), and nine species designated as Vulnerable (VU). Five more species have been designated as Near Threatened (NT). Data Deficient (DD) was applied to two species that lacked specific distributional information.
Because of their widespread distribution on the island, the remaining nine species were designated as Least Concern (LC). Along with endemic species, 36 native species were evaluated, with only eight classified as endangered. In addition, five species have been designated as Near Threatened, while five others have been designated as Data Deficient. The remaining 20 species have been classified as Least Concern.
Factors affecting freshwater fish
Prof. Devaka Weerakoon, a consultant at the Biodiversity Secretariat, explained that the most abundant fish are native to Sri Lanka and are restricted to rivers and streams in the first peneplain of the wet zone, and their habitats are generally found outside the protected area network. Similarly, the habitats of several other point endemic species, including Systomus asoka, Rasbora armitagei, and Ophichthys desilvai, are entirely outside of protected areas, making them vulnerable to a wide range of harmful human influences. Therefore, several are in jeopardy.
According to Sri Lanka’s National Red List, deforestation in catchment areas, as well as the removal of stream and riverbank vegetation that is prevalent in the wet zone for agricultural purposes and construction projects, is a major threat to the survival of some fish species. Tea plantations on a small and medium scale are recognised as the primary cause of deforestation in the wet zone’s lowlands.
Because the forest floor’s water regulation function is no longer available once the forest cover is removed and replaced by a different land use type, such deforestation will result in significant changes in flow regimens, particularly for small streams and rivulets, which tend to have high flows during rainy days and dry out quickly when there is no rain.
Deforestation and the removal of streamside or riverine vegetation also promotes soil erosion and sediment movement into streams and rivers, resulting in a change in water quality. Accordingly, because sediment deposition has been shown to affect the breeding and foraging ecology of many freshwater fish species, the streambed will change. River diversion projects for hydropower generation, drinking water, irrigated agriculture, and flood mitigation, he explains, are another factor affecting freshwater fish.
These projects alter the flow regime of a stream or river, causing a variety of changes in these freshwater ecosystems. Reduced carrying capacity, reduced water quality, temperature variations, increased predation rates, reduced wetted perimeter, and stream/river bed alteration are just a few examples. Furthermore, these changes in flow patterns have the potential to result in the eradication of microhabitats. As a result of these changes, several endemic and threatened freshwater fish species have been lost or displaced. Mini hydropower construction, for example, has had an impact on the breeding habitat of Systomus asoka.
Many fish species’ habitats have been fragmented as a result of the construction of large dams such as Polgolla, Victoria, Randenigala, Rantembe, Moragahakanda, and Kalu Ganga. Macrognathus aral and Labeo lankae populations, which were once widespread and widely distributed, have declined dramatically in the last decade and have mysteriously disappeared from many of their original locations. Prof. Weerakoon stated that numerous exotic plants and animals have been intentionally or unintentionally introduced into natural habitats, and that some of them have become invasive alien species, affecting native species directly or indirectly. He claims that over 30 alien fish species have been introduced, with any of these species used to boost inland fisheries. He also spoke about gem mining, urbanisation, and pollution emissions.
He claims that gem mining has a direct impact on many rivers and minor streams, particularly in the foothills of the wet zone. Soil erosion caused by gem mining increases the rate of siltation in streams and rivers, affecting water quality and causing changes in the streambed as a result of sediment deposition.
Prof. Weerakoon said most urban areas are located on the banks of wet zone rivers, and the expansion of urban areas results in large-scale releases of waste water and other pollutants into rivers, which has a direct impact on freshwater fish species. The reclamation of lowland marshes and swamps, particularly in the Western Province, has also resulted in local extinctions or significant reductions in species numbers.
The water quality of many suburban water bodies has deteriorated dramatically, according to the National Red List of Sri Lanka, due to the accumulation of harmful substances emitted by industries or wastewater discharged by households. There are also several solid waste disposal facilities near freshwater habitats, such as Karadiyana and Kerawalapitiya, as well as Bolgoda Environmental Protection Area and Muthurajawela Sanctuary.
This results in the discharge of leachate, which contains a variety of contaminants such as heavy metals and polycyclic aromatic hydrocarbons. Minister of Environment Mahinda Amaraweera explained that the fish he used to see in paddy fields have vanished, not only in paddy fields, but also in dam and river water, citing the dramatic change that has occurred over the last two decades. Everyone now understands, he claimed, that the main reason for this is the use of chemicals on plants, which pollutes Sri Lanka’s water supply.
He also stated that the harm done to fish and other wildlife in Sri Lanka is concerning, which is why the Government intends to import environmentally-friendly automobiles. Dr. Anil Jasinghe, Secretary to the Environment Ministry, emphasised the importance of close collaboration with the Ministry of Tourism to put Sri Lanka on the map for its higher value of fauna and flora. He contended that their Environmentally Sensitive Areas Recognising Project will identify over 200 sensitive areas critical to the conservation of species on the National Red List.
He also believed that implementing a ‘GO-Management’ strategy is critical to ensuring that specific economic models are linked in these sensitive areas. Paul Watson, a Canadian-American marine wildlife conservationist and environmental activist, said, “If we wipe out the fish, the oceans are going to die. If the oceans die, we die. We can’t live on this planet with a dead ocean.” This necessitates immediate and well-planned conservation measures, at least for those species that are not only unique to Sri Lanka, but are also under threat from human activity.
The Biodiversity Secretariat recommended an urgent islandwide systematic study of Sri Lanka’s freshwater habitats to ensure that the country’s freshwater fauna is fully inventoried. They also stated that population surveys for at least the 12 Critically Endangered Species, as well as conservation plans for at least the 12 Critically Endangered Freshwater Fish, should be conducted. Finally, the secretariat proposed developing conservation measures that involve local populations in freshwater fish conservation action, at least for restricted-range species, citing the fact that most freshwater fish species live in human-dominated ecosystems.