Sand mining and widening of the water bodies in marshes in an unchecked manner have upset the urban wetland ecosystems and contributed to the spread of invasive alien freshwater fish, Young Zoologists’ Association (YZA) Senior Instructor Shantha Jayaweera said.
Speaking at a press conference titled “Wetlands restoration, threats from invasive species and the Government inaction” organized by the YZA at the National Library and Documentation Services Board on Wednesday, he said that there are about 30 invasive alien freshwater fish species in Sri Lanka, and 15 of them are found in marshlands near Colombo.
“I have not seen that many invasive alien species in any other ecosystem. A scavenger known as ‘Suckermouth Catfish’ is rapidly breeding, and ‘Mayan Cichlid’ is a more recent addition to the list. Usually, the breeding season of ‘Mayan Cichlid’ is from April to May, but in Sri Lanka this fish species is breeding throughout the year. This fish cannot be mixed with other fish as it attacks them. It will be a disaster if this fish gets into our tanks. They are found in large numbers in Bolgoda Lake,” he observed.
Jayaweera said the population of local fish species is shrinking due to the spread of invasive alien species. “There are about 100 freshwater species in Sri Lanka and about 30 out of them are found in urban wetlands near Colombo. The population of some of them have shrunk considerably. For example, an endemic species known as ‘Sri Lanka Walking Catfish’ (Magura), which was a frequent sight about 25 to 30 years ago, is hard to find now,” he noted.
He pointed out that deepening the water bodies in and around Colombo has created favourable conditions for the spread of invasive species such as ‘Mannaya’ (Knifefish). “Now this species can be found as far as 75km inland through the Kalu Ganga. It prefers still water. When there is flooding it spreads in inland water bodies,” he added.
Jayaweera observed that the canal around the Heen-Ela marsh, which was not more than 15feet about 20 years ago, is now as wide as 30 to 40 feet. He also mentioned that deepening the water bodies in urban wetlands was one main reason for the growth of the crocodile population in them.
He pointed out that even though Kotte, Heen-Ela and Kolonnawa wetlands have been declared as sanctuaries in 2021, no action has yet been taken to properly communicate that, adding that not even a signboard has been put up at the sites.
YZA Senior Instructor and Environmental Lawyer Dr Jagath Gunawardena questioned the importation of ‘Pacific Whiteleg Shrimp’ to Sri Lanka, observing that no risk assessment has been conducted to date on its introduction to the Sri Lankan ecosystems.
“It was first brought into the country in April 2008, and it took until December 2018 for the Environment Ministry to instruct a risk assessment on it, but the importer is yet to conduct it. This species has been brought into the country a few times now and it has been released for shrimp cultivation in areas such as Puttalam and Mannar. It can be found in wetland ecosystems now. The Wildlife Conservation Department confirmed to us that it has given no permission to import this shrimp. Then how come it came into the country through the Customs, violating the Fauna and Flora Protection Ordinance, and whose influence was behind it?” he questioned, adding that laws and national policies are redundant when no action is taken against the offenders who openly violate them.
YZA Environment Working Committee Vice Secretary Lakshitha Edirisinghe said that the release of lands belonging to the Vidithalathivu Nature Reserve for shrimp cultivation was against the Mangroves National Policy of 2020.
YZA Research Committee Vice President Sajini Gamage said that the YZA is presently engaged in a study on fauna and flora diversity in the Sri Jayawardenepura Kotte Sanctuary. She said that the YZA conducted studies on fauna diversity in the Diyasaru Wetland Park and Bellanwila-Aththidiya in 2020 and 2021 respectively. The YZA had conducted a study on fish diversity in Beddagana Wetland Park in 2022.
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