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On cards, a piscine apocalypse in Kerala
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The brackish water habitats of Vembanad and Ashtamudi lakes are under severe pressure due to multiple factors, including hydrological regime change, pollution, invasive species and illegal fishing practices

October 06, 2022 07:13 pm | Updated October 07, 2022 10:02 am IST - KOLLAM

A view of Ashtamudi Lake in Kollam.

A view of Ashtamudi Lake in Kollam. | Photo Credit: C. SURESHKUMAR

The brackish water territory stretching from Thrikkunnapuzha to Thottappally used to be a rich fishing ground and a key source of income for many, but not anymore. 

Salam, an inland fisher from Alappuzha, says the waterbody is slowly going fallow, threatening everything, including his livelihood and tradition. He has seen some coveted species vanishing from the backwaters while some others have become increasingly rare. Kumaran, a fisher from Dalavapuram in Kollam, is puzzled by the collapse of clam stocks. He says clam beds are disappearing at alarming rates and there is a drastic decrease in survival rates. Baby from Kumarakom, the picturesque tourist destination, feels they are headed for a piscine apocalypse. Terrified by the depletion of fishes, he says the waterbody will be beyond redemption very soon. 

All the three fishers depend on Vembanad and Ashtamudi wetlands for their livelihood. The loss of faunal resources is only one of the issues threatening these Ramsar sites. Though the fishers had noticed the depleting trend some four years ago, they were hopeful of stock replenishment until recently. But now they feel many commercially important species are about to hit the critical point of no return, triggering a diversity crisis. “I have been fishing in Kayamkulam Lake for over 40 years and currently, we are witnessing an 80% dip in catch. Sustainable fishing is all theory than practice and at present the ecosystem is in a very critical state,” says Salam. 

More than 60% of the inland fishers in Kerala depend on Vembanad for their livelihood while it is also a source of sustenance for hundreds of others engaged in allied activities in Alappuzha, Kottayam and Ernakulam districts. “ Kuttanadan aattu konchu (giant freshwater shrimp), the most-sought after species in the lake, is going extinct as its production has come down to 27 tonnes from around 400 tonnes over the years. The Thanneermukkom Bund constructed to promote paddy cultivation divides the lake into two zones and the southern parts have been facing adverse ecological conditions for long. The area has 11 clam collectors’ societies and most of the clam collectors are jobless today,” says Charles George, president of the Matsya Thozhilali Aikya Vedi and a member of the State Fisheries Management Council. He adds that many parts like Muhamma and Kumarakom have become ‘aqua deserts’ and keeping the bund open for a longer period is the only way to stabilise the ecosystem.

Dip in species diversity

The aquatic ecosystems of both Ashtamudi and Vembanad have changed over the years. While faunal resources are fast depleting, the backwater habitats are under severe pressure due to multiple factors, including hydrological regime change, pollution, invasive species and illegal fishing practices. Aattu konchu, the lucrative prawns of inland waters, is fast vanishing from many parts of Vembanad Lake while pearl spot population has been dwindling in the creeks of Ashtamudi. The first fish census of Ashtamudi Lake jointly carried out by the Ashoka Trust for Research in Ecology and the Environment (ATREE); Department of Aquatic Biology and Fisheries, University of Kerala; and the Department of Fisheries in March 2022 had revealed a decline in species diversity. According to available data, Ashtamudi had the presence of 158 species in 60 families, but the fish census recorded and collected only 51 species. There was also an increase in the presence of marine species even in the freshwater zone, indicating a decline in the flow of freshwater from the Kallada river. Along with commercially important species such as pearl spot (karimeen) and mullet (kanambu), the lake is an abundant source of yellow clam (Paphia malabarica), India’s first Marine Stewardship Council (MSC) certified species. While the clam beds have been shrinking, a decline in the mean size of the pearl sport (Karimeen) and mud crab (Kaayal Njandu) was also recorded. As per the findings of the Vembanad Fish Count-2022, only 43 finfish species and five shellfish species were found in the lake compared to the 100 species recorded during the previous count. “But compared to Vembanad, Ashtamudi has a slightly healthier ecosystem and species diversity. Vembanad is plagued by a wider range of issues,” says A. Biju Kumar, Professor and Head, Department of Aquatic Biology and Fisheries, University of Kerala.

Climate change

According to experts, the bottom topography of the lakes has been changing rapidly while seawater influx is spreading to deeper areas in some parts of Ashtamudi. “Sea level rise is one reason and the impact of climate change is quite visible when it comes to aquatic ecosystems. Unseasonal rain and fluctuations in water temperature affect the breeding of many species. There are some species that cannot breed in low salinity and continuous bouts of intense rain will disrupt the process. Lack of hydro-climatic factors that instigate breeding will lead to a dip in population,” says K.K. Appukuttan, former scientist of the Central Marine Fisheries Research Institute (CMFRI).

In 2021, the Fisheries department was forced to push the start of the annual three-month ban on clam harvest in Ashtamudi Lake from December to January 2022. Though the spawning season was expected to begin by November, there was no larval settlement even during December. The waterbody could not achieve the salinity level required for the process due to the change in hydrological variables such as temperature and pH. The growing presence of marine fish in the freshwater zone is another indicator of climate change.

Compared to Vembanad, Ashtamudi has more marine varieties, climate-induced regime shifts in the wetland ecosystem being one reason. While the presence of mackerel (ayala) and blochi (valavode) shoals were reported earlier, the fish census in 2022 had recorded three marine species, including muppiri, kaduva nanthal and cheru paara for the first time in the lake. The decline in freshwater inflow and increasing levels of saline intrusion make it impossible for many species to breed or survive in such conditions.

Habitat loss

The recent studies in Vembanad have revealed the presence of Nile tilapia, a highly invasive species and a serious threat to indigenous biodiversity. As per a report submitted to the Kerala State Biodiversity Board, the floods of 2018 had a devastating impact on fish habitats as some exotic species entered nearly all waterbodies of the State during the period. While some predatory species like Arapaima ( Arapaima gigas) and Alligator gar (Atractosteus spatula) were identified, experts believe there can be many more invaders in the natural waters of Kerala. Escaped from aquaculture enclosures and ornamental breeders during the extreme climatic event, these invasive alien species (IAS) can gradually displace indigenous species, leading to endangerment and extinction. They will also alter the nutrient chain and keep preying upon the native fish stocks, damaging the ecosystem and species composition. While there is no proper mechanism in place to monitor the growth of the invasive alien species and its subsequent impacts, the aquaculture systems often fail to follow the biosecurity protocol.

Meanwhile, the molluscan fisheries in Ashtamudi and Vembanad have been battling the bio-invasion of Charru mussel (Mytella strigata). The invasive bivalve has already established colonies in many creeks leaving no space for native species such as the yellow clam. Since Charru can survive across salinity gradients, it spreads too fast preventing the settlement of native mussels. The increase in the biomass of Charru is also causing a negative impact on pearl spot population as the bivalve feeds on fish eggs and hatchlings.

Similarly, water hyacinth is another invasive species that contributes to habitat degradation by spreading thick weed carpets over the waterbodies. “It blocks the penetration of sunlight and affects oxygen diffusion. Oxygen depletion results in biodiversity loss. Infestation of this exotic weed is a serious threat to aquatic flora and fauna,” says G. Nagendra Prabhu, associate professor of zoology and principal investigator, Centre for Research on Aquatic Resources of Sanatana Dharma (SD) College, Alappuzha. The fast-spreading weed with its dense canopy is highly resilient while anthropogenic factors and climatic conditions of the State also help its expansion. “The weed causes water loss through evapotranspiration and if we leave it untouched for some years, the waterbody will be converted to a marshy land. At present, we are opting for quick-fixes like physical removal which is not a solution to the menace,” adds Dr. Prabhu.

Dredging for the National Waterway and other constructions too have left their impact on the ecosystem. Fishers complain that the sand dredged was deposited in the lake itself, resulting in a string of zonal changes. “Construction of a bridge in the Dalavapuram area along with the sand deposits have changed the pattern of currents in Ashtamudi Lake. At present the water flow to some creeks remains blocked during low tide. When sand deposits increase, certain species cannot survive as they need clay and salinity,” they say.

While the mangrove cover has improved over the recent years, the protection of intertidal zones is another area of concern. “Plankton production is very high there and the area provides habitat for a variety of flora and fauna, including migratory birds. But our measures to protect intertidal zones are highly inefficient,” says V.K. Madhusoodan, mangrove expert and environmentalist.

Anthropogenic factors

According to experts, some high-saline, estuarine and freshwater regions of the wetland ecosystem are under severe stress due to anthropogenic factors. “Vembanad is a biodiversity hotspot with several endemic species and its environmental conditions are also diverse. Pollution is a critical issue as a large amount of waste from the tourism and plantation sectors end up in the lake,” says K.G. Padmakumar, Director, International Research and Training Centre for Below Sea Level Farming, Kuttanad. He points out the dip in fish production that has come down to 4,500 tonnes from nearly 23,000 tonnes in the 1960s. “ Aattu konchu needs saline water for breeding, but their migration was blocked by the Thanneermukkam Bund leaving them on the verge of extinction. While salinity levels have increased in Ashtamudi due to Kallada Dam, the opposite has happened in Vembanad. As a result species diversity has decreased in both the waterbodies.” 

While juvenile fishing is very common among stake net operators, both Vembanad and Ashatmudi have a large number of unlicensed Chinese net units. Bush park fishing, another unscientific method using aggregates, is also very common as many artificial habitats can be seen in Ashtamudi and Vembanad. “Kuttanad paddy lands see a massacre just before cultivation as the fish are pumped out as part of dewatering. With traditional petti and para system getting replaced with centrifugal pumps, the fish are unable to survive. Instead of indiscriminate killing, we should allow this fish to go into the lake, but we hardly take any such measures to protect the biodiversity,” adds Dr. Padmakumar. 

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