A fish census carried out in Sasthamkotta Lake, the largest freshwater lake in the State and a Ramsar site, has revealed a decline in piscean diversity, an indication of the deterioration of environmental quality.
The census conducted by the Department of Aquatic Biology and Fisheries, University of Kerala, with the support of the Kerala State Council for Science, Technology and Environment and Indian Science Congress Association last month, found a dip in the population of both commercially valuable and rare species. The survey showed the presence of 17 species of fish, down from the recorded diversity of 30 species.
The decline in fish species had jeopardised the livelihood of traditional fishers, forcing them to shift their operations to other waterbodies. Less than 10 fishermen were dependent on the lake these days, the study found.
The survey conducted among fishermen in the neighbourhood of the lake revealed the total disappearance of once common species like Malabar Labeo (Labeo dussumieri) and Naadan mushi (Clarias dussumieri).
More importantly, it could not locate the Karimeen (Etroplus suratensis), Butter Catfish (Ompok spp.) and Malabar Spiny Eel (Macrognathus guentheri). “These commercially valuable species may not have disappeared from the lake but their absence in the catch indicates a considerable decline in population,” says A. Biju Kumar, Head, Department of Aquatic Biology and Fisheries.
The survey team has concluded that the primary reason for the decline of fish diversity in the lake is the loss of breeding grounds due to heavy siltation and the accumulation of weeds, especially in the shallow margins. Urban pollution was also found to be affecting the bioresources.
The study found that the increase in water temperature due to climate change was forcing fishes into deeper areas of the lake.
Volunteers used cast nets, gill nets and hook and line to cover the entire stretch of the lake over eight hours to record the catch. The dominant species recorded during the census was Filament Barb (Dawkinsia filamentosa), known as Poovali paral in local parlance, followed by Orange Chromide (Pseudetroplus maculatus), also called Pallathi. The third most abundant species were the Day’s Glassy Perchlet (Parambassis dayi) and Yellow Catfish (Horabagrus brachysoma).
The census also recorded three species for the first time from the lake. These include Dwarf Snakehead (Channa gachua), Glass Carplet (Horadandia atukorali) and an unidentified species belonging to the Parambassis family.
The team has recommended steps to develop the lake into a sanctuary for indigenous fish species. It has also mooted measures for fish stock replenishment and conservation of the lake.
