Sun, Nov 09, 2014 - Page 5 News List

Masses of dead fish in Rio baffle scientists


Dead fish wash ashore on a beach at Guanabara Bay in Rio de Janeiro, Brazil, on Nov. 3.

Photo: AFP

Thousands of dead fish have begun mysteriously washing up in the polluted Rio de Janeiro bay that is to host sailing events at the 2016 Olympics — and experts are at a loss to explain why.

Guanabara Bay has already been the subject of concern among sailors who are to compete in Rio because of the human sewage that gets pumped into its waters.

The International Olympic Committee (IOC) has expressed confidence that Guanabara will be fit for purpose by the time of the Games.

However, the recent appearance of thousands of dead fish, and the foul stench of their rotting carcasses, has attracted further scrutiny with the Olympics less than two years away.

Scientists are baffled by the phenomenon, but say there is no evidence so far to suggest pollution is the cause.

The foul odor first took over the usually peaceful Paqueta Island, where cars are banned and the population of 4,500 people travels on horseback or bicycle among the only baobab trees in Brazil.

With the help of a bulldozer, a municipal company has removed 20 tonnes of dead sabalo fish — from the Clupeidae family of herrings and sardines — and four dead sea turtles.

“Tests showed that this is not a matter of chemical or toxic water pollution,” Rio do Janeiro State University oceanographer David Zee told reporters.

Leandro Daemon of the Brazilian National Institute for the Environment, or INEA, agreed that water testing had not identified any toxic chemicals or any unusual change in the water’s pH (potential of hydrogen), salinity or oxygen.

“We have no answer yet about what happened, but we can certainly exclude the hypothesis of a chemical pollution killing the fish,” Daemon said.

Not everyone is so sure.

Worried fishermen and islanders are pointing the finger at the petrochemical activities of state giant Petrobras.

Five of the fish were sent on Tuesday to the Federal University of Rio de Janeiro’s biology department for analysis, and the results are to be announced in a week.

Experts want to know if there are any signs of pollution or disease in the entrails or gills.

However, Zee said the likeliest scenario was that the deaths are caused by “thermal pollution” of the water.

“Sabalo are very sensitive to any lack of oxygen. Warm water temperatures such as those recorded several days ago — ranging from 27oC to 30oC — in shallow water decrease the solubility of oxygen,” Zee said.

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