BRAZIL'S DOLPHIN DEATHS

SCIENTISTS fear heavy toll traced to virus suggests an environmental issue.

Something ominous was happening in the turquoise waters of Sepetiba Bay, a booming port outside  Rio de Janeiro.

Beginning late last year, fishermen were coming across the scarred and emaciated carcasses of dolphins, sometimes five a day, bobbing up to the surface.

Since then, scientists there have discovered more than 200 dead Guiana dolphins, or Sotalia guianensis, a quarter of what was the world's largest concentration of the species.

The deaths, caused by respiratory and nervous system failures are linked to a virus, have subsided, but scientists are working, to unravel the mystery behind them.

How, they ask, did a virus that might ordinarily have claimed a handful of dolphins end up killing scores of them?

And does part of the answer, scientists and local residents ask, lie in the bay itself, at once a testament to Brazil's economic power and portent of environmental risk.

The dolphins are ''sentinels'', said Mariana Alonso, a biologist at the Biophysics Institute at the Federal University of Rio de Janeiro, one of a number of groups working to understand the epidemic.

''When something is wrong with them, that indicates the whole ecosystem is fractured.''