A comprehensive study on fish diversity of Bharathapuzha, the largest west-flowing river in Kerala, found it as the richest in fish species among the rivers in Kerala. It recorded the presence of 117 species, with three species endemic to the river.
The study, conducted jointly by Department of Aquatic Biology and Fisheries, University of Kerala; Conservation Research Group, St. Albert’s College, Kochi; and the Department of Zoology, NSS College, Ottappalam, shows that despite the ecological degradation across the river basin, “Bharathapuzha turned out to be one of the richest among the State’s rivers in terms of fish diversity.”
The fish species endemic to the river include Silent Valley stone loach (Balitora jalpalli); Pambar Banded Loach (Mesonoemacheilus remadevii); and the catfish Pseudolaguvia austrina.
Although the Kunthipuzha stream of the Thoothapuzha tributary flowing through the Silent Valley National Park had the lowest species richness (25 species), it has very high conservation value, as two endemic species — Balitora jalpalli and Mesonemacheilus remadevii — are restricted to this stream, highlighting the importance of protected areas such as Silent Valley in the conservation of endemic biodiversity, the study said.
It said 28 per cent of fish species (33) that occur in the Bharathapuzha are endemic to the Western Ghats. The catfish Pseudolaguvia austrina occurs as small fragmented populations in the Kanjirapuzha and Thoothapuzha rivers.
The Kunthipuzha stream of the Silent Valley National Park had been surveyed in the past by several researchers and the results of this study shows 25 species, thereby increasing the number of freshwater fishes known from the national park.
“However, this number cannot be considered as the actual diversity of the national park because several additional species are found in the east-flowing Bhavani river and the Kadalundy river (draining the western segment of the buffer zone), which is not mentioned here” said Dr. Rajeev Raghavan of Conservation Research Group.
A little more than one tenth of species (12 per cent; 14 species) that occur in the Bharathapuzha are listed as threatened in the IUCN (International Union for Conservation of Nature) Red List of Threatened Species. This includes one species listed as Critically Endangered (Hemibagrus punctatus), six each listed as Endangered and Vulnerable. Thoothapuzha tributary had the highest number of threatened species (10), the study found.
A. Biju Kumar, Head, Department of Aquatic Biology and Fisheries, University of Kerala, said surveys were carried out in all the four tributaries viz., Gayathripuzha, Chitturpuzha, Kalpathipuzha, and Thoothapuzha of Bharathapuzha and the Kunthipuzha stream (of Thoothapuzha tributary) flowing through the Silent Valley National Park at multiple intervals from January 2004 to February 2013.
“Bharathapuzha comprise one of the sixteen catchments in the southern Western Ghats that has the highest species richness and endemism of freshwater taxa (a group of populations of organisms) including fish, mollusc, and odonates,” the study said. According to Dr. Sanjay Molur, Executive Director of Zoo Outrearch Organisation, it is also one of the five catchments along with Periyar, Pamba, Manimala, and Chaliyar that qualify as potential freshwater ‘Key Biodiversity Areas’ (KBAs).
Dr. Biju Kumar, who initiated the study in 2004, said that “several anthropogenic stressors including deforestation and loss of riparian cover, dams and other impoundments, pollution, sand-mining, non-native species, climate change, and destructive fishing practices are threatening the fish diversity of Bharathapuzha.” Further, Bharathapuzha watershed experiences an average annual rainfall of 2,500 mm, which is about 17 per cent less than the State average. “Recent studies have observed changes in both rainfall and temperature in the river basin. These climate change phenomena in the Bharathapuzha watershed will have its serious repercussions on fish fauna, which remains to be investigated further,” he said.