Warming of Arabian Sea poses threat to fisheries: Scientists

Indian scientists have spotted unusually high warming of the Indian Ocean in the recent years, which may lead to depletion of fish cache in the western sea board in future.

The warming have led to sharp decline in phyto-planckton — tiny marine plants and insects — that is the major food source for many aquatic creatures including fishes.

While historical simulations indicate marine phytoplankton population was reduced up to 20 per cent in the last six decades, satellite data show the decline is up to 30 per cent in the western Indian Ocean in the last 16 years. The last 15 years was the warmest years recorded in the global meteorological history.

“We find declining plankton trends are due to rapid warming in the Indian Ocean, which suppresses nutrient mixing from subsurface layers. Future climate projections indicate Indian Ocean will continue to warm, driving this productive region into an ecological desert,” said Roxy Mathew Koll, a scientist at Indian Institute of Tropical Meteorology, Pune.

One of the consequences, argued Koll, was a drop in tuna fishing in the Arabian Sea and western part of the Indian Ocean.

Though India continues to be major player in the global tuna market, the catch decreased sharply in the last 50 years in the Indian Ocean, according to data from the Indian Ocean Tuna Commission.

The tuna catch rates in the Indian Ocean have declined by 50-90 per cent in the past five decades. While part of the decline is related to an increase in industrialised fishing activities and loss of phyto-plankton — food for the fish — may be adding to the stress as large-scale distribution of tuna and other fishes were associated with phytoplankton availability and abundance.

The UN Food and Agriculture Organisation data suggest Indian Ocean accounts for 20 per cent of the global tuna catch, especially the most economically valuable big-eye tuna, making it the second largest supplier to world markets.

“In the last 100 years, Indian Ocean was warmed by 0.8 degrees Celsius and the warming trend is expected to continue. In the same period, Indian land mass was warmed by about 0.5 degree Celsius. The ocean is warming faster than land,” he told Deccan Herald. Six other institutes are involved in the study published in the Geophysical Research Letters.

Though Indian Council of Agriculture Research is aware of the problem, the study by Koll and his colleagues provides a broad picture of the declining trend over a larger area. “Our study indicates a further decline in phytoplankton in the Indian Ocean, suggesting the vulnerability of the marine ecosystem,” Koll added.