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Warming sparks smaller-fish fears

New Delhi, Sept. 30: Fish in India’s coastal waters and elsewhere in the world’s oceans might become smaller and lighter in the coming decades, a study of the effects of climate change on fish physiology has suggested.

The computer simulation study of the impact of warmer and less-oxygenated oceans on some 600 species of marine fish has predicted that their average body weight in 2050 would be 14 to 24 per cent less compared with 2001.

The Canadian and US scientists involved in the research have found that most of the species they studied could experience a five to 39 per cent drop in their maximum body weight. The findings were published today in the journal Nature Climate Change.

“These results may have implications for the marine ecosystem and for food security,” William Cheung, marine ecologist at the University of British Columbia in Canada and lead author of the study, told The Telegraph.

But a senior Indian scientist said the fishing zones for at least two fish species in Indian coastal waters had expanded over the past two decades and there was no evidence of size depletion driven by climate change.

The simulations by Cheung and his colleagues predict the largest decrease in the average maximum body weight of fish in the Indian Ocean (24 per cent), followed by the Atlantic Ocean (20 per cent) and the Pacific Ocean (14 per cent).

According to the projections, the maximum body weights of some fish species found along India’s west and east coasts could fall by more than 20 per cent.

The projected reductions in fish size and weight are accentuated closer to the coasts rather than in deep-sea zones.

“This is because changes in the oceans’ properties that influence fish physiology will be greater in shallow areas than in the deep sea,” Cheung said.

The study is part of efforts to predict how warmer temperatures brought about by greenhouse gas emissions would effect the marine ecosystem. Last year, scientists at the University of Aberdeen in Scotland had independently shown that warmer temperatures are likely to reduce the maximum size of the haddock off the Scottish North Sea coast.

Most earlier studies had already indicated that warmer oceans could significantly change the geographical distribution or productivity of marine fish. “This study shows that the effects of global warming could be even greater than previously expected,” Cheung said.

But the head of India’s Central Marine Fisheries Research Institute in Kochi cautioned that the marine ecosystem, particularly in the tropical regions, was complex and remained poorly understood by scientists.

“We’ve actually seen some positive changes in the geographic distribution of the Indian oil sardine and the mackerel,” G. Syda Rao, director of the institute, said.

About 30 years ago, both these species were primarily found off the coasts of Karnataka and Kerala. But, Rao said, the oil sardine is now found further north, even off the Gujarat coast, and off India’s east coast.

The mackerel too is now found along the east coast, off Bengal and Odisha, Rao said.