Fisheries department suggests dredging Kosasthalaiyar river bed to remove alien species

CHENNAI: The state fisheries department has informed the southern bench of the National Green Tribunal (NGT) that pillars and fly ash from the thermal power plant are acting as a catalyst for the species invasion and suggested the removal of invasive Charru mussel (Kakka Aazhi) for a total length of 23 km in Kosasthalaiyar River.

In a report to the NGT, which is hearing a case about the ecological damages due to the invasion of Charru mussel in Ennore Creek, the fisheries department said that settlement of the invasive mussel Mytella strigata (Charru Mussel) had thickly spread throughout the bottom with heavy settlement on hard substratum like pillars of bridges, and hard underwater mud banks formed by the fly ash and clay.

Moreover, a joint inspection revealed that Charru mussel invasion was found to be relatively low in sites where phytoplankton density was high, which shows that mussel invasion limits phytoplankton productivity, which in turn affects the availability of other fauna, including prawns. Invasive mussels have grown and covered the bottom like a carpet, likely impacting the survival of bottom feeders like prawns, which corroborates the claims of the local fishermen.

Explaining to the Tribunal that the invasive species only can be removed by dredging, as the entire river bed has been mounded, the department suggested to initiate dredging at a stretch of 23 km from Ennore creek to Pulicat river mouth at a time in the first phase and that disposal of mussel bed would be transferred to far off place from the area of dredging to prevent re-entry.

Studies conducted by Dr MGR Fisheries College and Research Institute, Ponneri, reveal that a reduction in salinity influenced by freshwater influx would lead to mass mortality of the Charu mussel. Mussels less than 5 grams of body weight are found to be immature, and mussels with 6-7 grams of body weight are found to have mature gonads. During the monsoon period, the Kosasthalaiyar/Ennore backwater is usually flooded with freshwater. Dredging may be carried out immediately after the monsoon season, that is, January, to restrict further growth of the mussel.

“To restore the native ecosystem in the Ennore Creek after dredging, indigenous species like Shrimp (Penaeus indicus), Mullets (Mugil cephalus), Milk Fish (Chanos chanos), Green Mussel (Perna viridis), Edible Oyster (Crassostrea madrasensis), and others may be ranched,” the report said.

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