Indiscriminate, excess fishing has significantly reduced the catch of local favourites, like Bombay duck and pomfret, over the past decade, with the drop being up to 55% in some species, according to new data from the Central Marine Fisheries Research Institute (CMFRI).
Meanwhile, rising sea temperatures have boosted small fish populations, like oil sardines and mackerels, expanding their territory in the past two decades from their traditional habitat off the southwest coast eastwards up to Kolkata and northwards to Mumbai.
Overall, fish catch in Maharashtra declined by 15% in the last decade, according to a CMFRI analysis that compared five-year averages of annual landings between the 2002-06 period and 2007-11. Bombay duck and pomfret each declined by around 25%, sharks and rays by 28%, and prawns by 35%. Perches, including rawas, declined by 42%.
"All fishes traditionally characteristic of Maharashtra are declining because of overfishing, while new fish resources are coming up due to climate change," said V D Deshmukh, senior scientist in charge at CMFRI's Mumbai office, which has done the analysis.
Of most concern perhaps is the fate of the state's famous Bombay duck. As with other fish, catch rose through the 1960s and '70s due to increased mechanized fishing.
But the five-year average of annual landings of the fish has reduced by more than a third from 30,000 tonnes in the 1980s to around 20,000 tonnes now, according to CMFRI. Fishing pressures may also be causing this fish to mature earlier, producing fewer eggs.
Only a few, low-value species saw an increase.: sardine (taarla) catch went up by 142%, mackerel (bangda) by 133% and tuna by 70%. Until the late 1990s, sardines and mackerel were rarely found north of Ratnagiri.
If the decline continues, the new home for Bombay duck, albeit a different species, may be West Bengal; catch of the fish has increased in that state as well as in Orissa as fisheries in the east have developed in recent years.
Silver pomfret has also been severely affected, with its five-year average of annual landings dropping almost 80% from 24,000 tonnes in the 1980s to just over 5,000 tonnes in recent years, said Deshmukh.
In fact, of 25 important fish stocks in the state, only two species are still abundant, found a CMFRI assessment from 2007 to 2011. More than half are in decline. The drop in stocks is due to overfishing and the increased demand for certain seafood. Fish stocks here can sustain around 8,000 boats with reasonable profit, according to CMFRI estimates, but the actual number of boats plying the region is over 17,000. Of these, around 5,600 are trawlers—almost twice the optimal number.
Boats are also catching younger, smaller fish, giving populations less of a chance to reproduce.
Climate change may add to the pressures on local stocks. Larger fish tend to be more sensitive to environmental changes. Sea surface temperature increased by 0.2 to 0.3 degrees Celsius along the Indian coastline between 1960 and 2005, and is projected to increase further by 2 to 3.5 degrees C by 2099.
Small fish like sardines thrive in warmer temperatures, however, making it easier for them to adapt. Sardine expansion beyond the Malabar zone was first seen in Tamil Nadu in the late 1980s, according to E Vivekanadan, an emeritus scientist with CMFRI, based in Chennai. In Tamil Nadu, the fishery was "almost zero 25 years ago, now it's 100,000 tonnes", he said. In the last year, he added, sardines have started appearing as far north as Dhaka.
On the west coast, sardines have extended as far north as Gujarat in recent years and their catch in Maharashtra has almost doubled. Mackerels are following a similar pattern, and are also being found in deeper waters.
These changes reflect global trends. Across the world's oceans, several fish populations are shifting in response to warming waters. Sardines have reinvaded the North Sea and Baltic Sea, while cod in the North Sea are venturing farther north toward the Arctic.
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