Changing salinity in the Sunderbans impacts fishing economy

Moushumi Basu The Pioneer 11 Apr 11;

Sunderbans (West Bengal): With fishing being the predominant source of livelihood in the Sunderbans, the changing pattern of salinity here is seen creating an economic wedge between the fisher folk of the central and western sectors of the mangrove swamps.

According to a study, the rivers in the western part of the Hooghly estuarine delta due to fresh water feed from the Ganges provide prolific capture of fish of high commercial value both in India and abroad.

On the contrary, the fishing community around the high saline Matla estuary of the central Sunderbans is rendered economically vulnerable. They can at best hope to find a low priced fish that can just cater to the local community.

This changing phenomenon, according to experts, is believed to be due to an impact of climate change along with siltation of certain deltaic rivers and discharge from Farakka and other barrages on the Ganges.

Water in Sunderbans is seen to change its colour, taste and form at very creek — from the shallow muddy rivers to grey and emerald blue; from slender meanderings to several miles of wide rivers. And fish unmistakably rules the palate in and around the region.

“The nature of our catch today is as per the changing levels of salinity of the waters here,” says Khokon Mondal and his fellow villagers, all traditional fishermen from Pathorpaara in Satjelia islands of central Sunderbans.

Perched on their small dinghies along with five other fishermen from his village, Mondal regrets, “The yield of good quality fish here has gone down drastically during the past few years — at best we can hope to capture fish as Lotte, Phasa etc, that can fetch a maximum of Rs 30-40 per kg”.

In sharp contrast the fishermen from the islands of Sagar, Namkhana, etc. in the west are fortunate to find fish as hilsa, parshe, bhangon, pomfret and shingee magur (catfish) which are high in demand sold up to Rs 500 per kg in the market. “Today, many of the fishermen in these islands are able to even afford trawlers, with much bigger nets enabling more catch”, they pointed out wistfully.

Explaining this contrasting phenomenon, Dr Abhijit Mitra, Head of Department of Marine Science, Ballygunge Science College, University of Calcutta, said, “The impact of climate change on the aquatic ecosystem is an interlinked event between the melting of Himalayan glaciers feeding the Sunderban rivers and their subsequent alteration of salinity.” Further, anthropogenic or human-intervened factors such as barrage discharge also contribute to the varying salinity pattern of these rivers.

Hence salinity changes here are indirect but potentially sensitive indicators for detecting the threats due to climate change. “These alterations are reflected in the faunal and floral community of the said area,” Mitra felt.

An ongoing study on climate change and impact of salinity alteration in Sunderbans, conducted by the Department of Marine Science, has shown that the rivers of Sunderban delta have two distinct water characteristics at the central and western estuaries of the Matla and Hooghly, respectively.

The rivers in the western sector (Hooghly and Muriganga) are connected to the Ganga-Bhagirathi system of Himalayan glaciers. Their estuaries are thus “freshened up” with melting glaciers coupled with increased discharge of excess rainwater from barrages.

In sharp contrast, rivers of central part of Sunderban delta are deprived of fresh water inflow from Himalayan glaciers, due to heavy siltation of the erstwhile Vidyadhari river.

The latter was the main connect of the rivers (Matla, Thakuran, Gosaba and Harinbhanga rivers) of the central sector with the Himalayan glaciers.

As a result the rivers are turning hyper-saline in nature, due to tidal water feed from the Bay of Bengal, says the report.

“The footprints of climate change are, therefore, perceived in these differing ways in these two sectors of the estuarine complex,” pointed out Mitra.

“The above effect is being visibly perceived in the fishing community”, observed Dr Kakoli Banerjee, Research Associate, Ministry of Earth Sciences Project, who is a part of the study team of the Dept of Marine Science, University of Calcutta.

Fish such as the hilsa and pomfret that are known to fetch good money in the market are no longer found in the central tide fed region. “Species as the hilsa are anadromous in nature and have feeding grounds in the sea and spawning grounds upstream,” she said.

Such fish ideally thrive in areas of optimum blend of fresh and saline water. The recent trend of increasing salinity in the central sector of Sunderbans has dramatically modified their migratory path towards the west, she added.

For similar reasons, Bangladesh on the eastern side of the Sunderbans continue to flaunt its tag of “world-famous hilsa from Padda river”, a tributary of the Ganges in Bangladesh. “The Bengal Basin is slowly tilting towards the east due to neo-tectonic movement — it is presently at three degree tilt towards Bangladesh”, said Rajrupa Ghosh, research team member from Marine Science Department.

This is forcing greater freshwater input to the Bangladesh Sundarbans, through River Padda than the Indian side. As a result, the salinity there is much lower than that of the Indian Sundarbans creating an ideal condition for the Hilsa to flourish, she said.

Signature species on the decline

In another interesting observation, the Sundari trees (Heritiera fomes), signature species of the mangroves, is vanishing from the central parts of the Sunderbans.

The tree derives its name ‘Sundari’ from its beautiful white and red inflorescence. Its blossoms, regarded as the most attractive of the 34 mangrove species here, are a rare sight.

“This phenomenon is also owing to similar reasons of inflow of fresh water on the western sector and Bangladesh Sunderbans, which is ideal for flourishing of these prized mangrove species,” said Dr Bannerjee.

The Sundari is found to be perishing from the central Matla estuarine tract, she added. This slow destruction of Sundari trees may be considered an effect of climate change, combined with other forms of anthropogenic stress, she said.