Survey underway to remove invasive alien species from Kosasthalaiyar

CHENNAI: As Charru Mussels (Kakka Aazhi), an invasive alien species, invaded around 5 kilometres of Kosasthalaiyar River affecting livelihood of fishermen, the Tamil Nadu State Wetland Authority and Water Resources Department has commenced bathymetric survey to remove the invasive species as well as to dredge the shallow portion of the river.

An official attached to the Authority said that the survey is being conducted to carry out selective dredging. "Around 1.63 lakh square meters of river, for a total length of 600 metres, will be dredged by the Water Resources Department. The portion is located 8 kilometres (near Kattupakkam) upstream from the Ennore Creek. Charru mussels have grown to look like small islands inside the river. Local fishermen and NGOs suggested the location for the survey," the official added.

Bathymetric survey is being conducted to measure the depth of a water body as well as map the underwater features of a water body.

The official pointed out that the initiative is based on a request from the fishermen. "Due to the invasive species, fish and prawn production has decreased. If the invasive species were removed and the river dredged, it would allow sea water to enter the river from backwaters and promote prawn production. However, we can not dredge the entire river as it may affect other native species. The project will benefit 9,000 fishermen families in the area," he added.

Even though the dredging completed in the selected portion, charru mussels would grow back over time. Continuous efforts should be carried out to spread, he said.

Once the survey is completed, the Water Resources Department will prepare a detailed project report and commence the dredging work.

During the last week of December 2022, fishermen from Kattupakkam and environmentalists from Save Ennore Creek Campaign, raised alarm on unchecked invasion by charru mussels in Ennore and Pulicat wetlands. They said that the invasive species spread like a carpet at the bottom of the river and prevent prawns from grazing or burying themselves in the sediment. The alien species is also wiping out the locally prevalent yellow clams (manja matti) and green mussels (pachai aazhi).