How invasive mussels pose a threat to man, marine life in Pulicat Lake

Ravi Kannaiyan, 50, and his 45-year-old wife Rani, have been spending hours fishing in the Pulicat Lake over the years. Earlier, a 10-hour fishing round at night ended with Ravi and Rani returning to the seashore with their boat filled with tiger prawns, jellyfish, finfish, and crabs. Now, they return with barely five kilograms of fish and nearly three kilograms of prawns.

The bigger worry, however, the couple is grappling with is to return with injuries because of the rise of sharp-edged invasive mussel species.

Fisherman A. Basker shows his bruised foot. Photos: Karunakaran B 

“The catch has reduced drastically. The amount of fish, crabs, and prawns has dipped drastically all because of the invasive mussels. Earlier, we got large-sized tiger prawns; now, we get small baby prawns, just-born fish, and small crabs. We have no other jobs and cannot think of anything else,” said Ravi Kannaiyan.

Hundreds of fishermen in Pulicat Lake, situated in the bordering areas of Tamil Nadu and Andhra Pradesh, share Ravi and Rani’s plight. They are returning to the shore with not just poor fish catches but also bleeding feet. The sharp-edged invasive mussel species spreading over the seabed of Pulicat Lake, which hampers the growth and reproduction of marine life, also pierces through the feet of fishermen when they get down from boats into the lake to collect their catch.

The green seagrass, serving as the primary food for lakhs of fishes, prawns, and other marine life at the Pulicat Lagoon is being encroached upon by the invasive South American Charru mussels.

The green seagrass, serving as the primary food for lakhs of fishes, prawns, and other marine life at the Pulicat Lagoon is being encroached upon by the invasive South American Charru mussels, found in Panama, Argentina, Brazil and Venezuela. Experts say this invasion is hampering the growth of sea plants and putting at risk the entire food chain.

Ravi and Rani spotted mussels in 2019 in a few fishing zones but had no idea of the serious threat they posed. Back then, the couple used to earn a minimum of Rs 1,000 a day when they went fishing, but now the earning has shrunk to Rs 500. Not only that, it has also become a venture fraught with risks.

Activists like Durga Moorthy warn that coastal regions are facing a severe ecological disaster with the bio-invasion of mussels.

Several fisherwomen in the busy Pulicat fish market sell the fresh catch brought by their men. The tiger prawn, a popular variety from Pulicat Lake, occupies a prime place at fish stalls. The fisherwomen say though the demand for tiger prawns is increasing, their men are unable to bring in the big catches now.

Fishermen at the Pulicat Lake assessing their catch.

The ‘sting’ of mussels

Fisherman A. Basker did not dream of getting injured when getting down into this five-foot-deep lake water. Sharp-edged mussels cut through Basker’s feet often now. Sometimes, he stitches the wounds using needle and thread meant for his nets.

The fishing method followed by Basker is unique. He and his partners, eight in a team, cast the net and wait for half an hour to gather fish and prawns. Once satisfied with their catch, they enter the water without disturbing the movement of the fishes and lift the net. They cannot wear slippers or shoes as the ground is slippery.

The Pulicat fishermen are being forced to think of alternative means of livelihood.

Showing the deep scars and fresh injuries on his feet, Basker said, “It impacts us badly. Mussels tear our nets and pierce our feet, but we carry on because it’s our job. The cut it makes is often very deep. Very sharp and big mussels in the creek pierce through our feet and sometimes split the thick skin.”

He added that many elderly fishermen, particularly those with diabetes, are worried about healing and are on the verge of quitting direct fishing and turning into dealers.

Baby prawns stuck with excreta

Large swathes of mussels are clearly visible in the lake. Fifth-generation fisherman 54-year-old K Arokiyam explained how his forefathers raised families with ease, as the marine wealth in the lake was never-ending.

“Pulicat Lake is an Akshaya Pathiram. For generations, our families have fished here. We knew the varieties of fish and prawns and the right time to fetch them. Now, we see mussels patches all over. We are confused about where to catch what variety of fish,” Arokiyam said while pushing his boat, which had halted after hitting a heavy mound of mussels.

Mussels eat away sea plants, dirt, and small marine creatures for their existence. Over time, their excreta forms a black waste layer on the lake's ground.

“Baby prawns that get stuck in the oily, slushy texture of mussel excreta do not survive. Many marine organisms are forced to look for safer places for reproduction. In the long run, the future of Pulicat fishermen looks bleak because of these mussels,” said Arokiyam.

The impact of mussels is not contained only to fisherfolk in Pulicat. While one segment of fishermen sells their catch to big dealers from Chennai, Kerala, and Andhra Pradesh, another segment sells their catch to small traders and women hawkers. Hundreds of women carry fish and prawns in big baskets and sell them in neighbouring villages. The catch from Pulicat Lake is essential for the survival of over 5,000 families.

Impact on winged visitors

The mussels have posed an existential threat to the entire ecosystem, including migratory birds, dependent on Pulicat Lake. Thousands of migratory birds go hungry as the mussels drive away fish and prawns.

Pulicat Lake Bird Sanctuary is a protected area and the second-largest brackish water lake, next to Chilka Lake in Odisha. Hundreds of migratory birds can be spotted in the lake between October and March every year. Among them, flamingos gather in large numbers, creating a picturesque spot for tourists and bird watchers.

Experts say Pulicat Lake hosts close to 15,000 greater flamingos a year, the highest anywhere in India. Now, these birds also struggle to find food due to displacement of marine life in the lake.

Neighbouring Kerala's ‘mussels pain’

The first reported invasion of mussels in south India was from similar tidal wetlands, namely Vembanad and Ashtamudi in Kerala, in 2017. Both wetlands are tidally connected to the Kochi port and harbor.

Professor and researcher Biju Kumar, who heads the Department of Aquatic Biology and Fisheries at the University of Kerala, has been studying the life and impact of Charru mussels. According to his findings, this mussel causes mass displacement of native mussels, is very tolerant, and reproduces rapidly.

“Controlling the spread of these mussels is not possible. The only way to reduce their growth is to harvest, dredge the patches, and clear space for native species to grow. These invasive mussels are very small but thrive once they find a comfortable space. It is essential to dredge the spots frequently,” Biju Kumar told The Federal.

Scores of fishermen in Tamil Nadu have reported this invasion to the Ministry of Fisheries and filed complaints with the National Green Tribunal in Chennai. As a result, the Tamil Nadu Fisheries Department recently held a meeting with fishermen to find solutions to eradicate invasive mussels.

“We suspect that Charru mussels arrived in coastal regions through unchecked discharge of ballast water stored in huge ships that come to the ports. The failure of port authorities to check proper discharge of ballast water resulted in the migration of invasive species from the hulls of visiting ships to our coastal areas,” said activist Durga Moorthy of the Chennai Climate Action Group, who attended the Tamil Nadu Fisheries Department meeting in Chennai.

While the demand for tiger prawns is increasing its supply has dwindled over the years in Pulicat.

She also observed that in a couple of fishing zones, the carpet of mussels has grown like hard rocks, impacting the movement of boats. The tidal movement is also affected by these hard patches.

“Officials have agreed to clear the accumulation in three spots in the Ennore coastal zone. This should be a regular activity until a scientific way is devised to remove the accumulation. The disaster is actually affecting fishermen and disturbing the entire coastal ecosystem,” she added.

It is time for the authorities to take cognizance of the issue and devise a strategy that is sympathetic to the plight of the fisherfolk and marine life.