Fish move north to beat the heat

Is your meal incomplete without that bit of fried fish?

Well, get ready to do without — or pay exorbitant prices for the treat.

Over the next 50 years, a new study predicts, India could lose up to 40 per cent of its fish populations as a result of global warming and climate change.

The study, conducted by the Sea Around Us Project at Canada’s University of British Columbia, was published in October.

But you don’t need to wait 50 years to start worrying. Fishermen — particularly in storm-riddled West Bengal — are being forced to go further out to sea as fish retreat from the coast in search of cooler waters.

While the effects on ecosystems will be significant, this would also endanger a vital food source in some of the more impoverished tropical coastal nations.

“Even 10 years ago, our fishermen used to haul at least 1,000 quintals of fish every year from the Bay of Bengal,” says Joykrishna Halder, secretary of the West Bengal United Fishermen Association. “Now we never catch more than 700 quintals a year.”

The main reasons are rising ocean temperatures and increasingly violent storms, says Manas Kumar Das, principal scientist and head of the Fish Health and Environment Division of the Central Inland Fisheries Research Institute (CIFRI).

CIFRI studies have shown that monsoon variations, frequent droughts and severe storms are also killing the fish in freshwater bodies inland and affecting breeding patterns.

In aquaculture farms along the Ganges, temperatures have risen by up to 1.6 º Celsius over the last three decades. In colder regions like Hardwar, temperature in the Ganges has increased by about 1.5 º Celsius.

“We’ve seen a geographic shift as some warm-water fish species move to cooler northern stretch of the Ganges,” says Das. “Some fish which were found in the middle and lower reaches 10 years ago are now only found in places in Hardwar.”

As the sea levels rise, saline water is contaminating freshwater bodies and aquaculture farms along the coast, says Pulak Lahiri, marine biologist and former professor of Calcutta University.

“Several fish — like some of our major Indian carp, including rohu and katla — will be eliminated from these areas if they cannot quickly adapt to the changing salinity levels,” says Lahiri. “Fish are very sensitive to temperature too and some species — those that can’t swim very far — may go locally extinct.”

Increased rainfall in the post-monsoon months of September to December has also resulted in breeding failure among major Indian carps.

The Sea Around Us study could be offering an optimistic view of the likely effects of climate change — it has not taken into account the effects of ocean acidification, caused by excessive carbon dioxide dissolving in seawater.

Scientists say this will reinforce the effects of warming on the oceans.

“Adding ocean acidification into the equation would further decrease future fishery potential,” says Lahiri.

For Haradhan Mondol, a fisherman from Patharpratima in South 24 Parganas, the outlook is disturbing.

“Our catch has already declined,” he says, holding a worn net that he uses in the streams that run through the Sunderbans. “Some fish, like the lata (Lates calcarifer) and guli (Mystus gulio) are just not found in the rivers anymore... we’re now forced to go deep into the sea.”