Animals

With high Andean peaks and a humid tropical forest, Bolivia is a country of ecological extremes. But during the Southern Hemisphere's recent winter, unusually low temperatures in part of the country's tropical region hit freshwater species hard, killing an estimated 6 million fish and thousands of alligators, turtles and river dolphins.

Scientists who have visited the affected rivers say the event is the biggest ecological disaster Bolivia has known, and, as an example of a sudden climatic change wreaking havoc on wildlife, it is unprecedented in recorded history.

"There's just a huge number of dead fish," says Michel Jégu, a researcher from the Institute for Developmental Research in Marseilles, France, who is currently working at the Noel Kempff Mercado Natural History Museum in Santa Cruz, Bolivia. "In the rivers near Santa Cruz there's about 1,000 dead fish for every 100 metres of river."

With such extreme climatic events potentially becoming more common due to climate change, scientists are hurrying to coordinate research into the impact, and how quickly the ecosystem is likely to recover.

The extraordinary quantity of decomposing fish flesh has polluted the waters of the Grande, Pirai and Ichilo rivers to the extent that local authorities have had to provide alternative sources of drinking water for towns along the rivers' banks. Many fishermen have lost their main source of income, having been banned from removing any more fish from populations that will probably struggle to recover.

The blame lies, at least indirectly, with a mass of Antarctic air that settled over the Southern Cone of South America for most of July. The prolonged cold snap has also been linked to the deaths of at least 550 penguins along the coasts of Brazil and thousands of cattle in Paraguay and Brazil, as well as hundreds of people in the region.

Water temperatures in Bolivian rivers that normally register about 15 ˚C during the day fell to as low as 4 ˚C.

Hundreds of penguins that apparently starved to death are washing up on the beaches of Brazil, worrying scientists who are still investigating what is causing them to die:

About 500 of the black-and-white birds have been found dead just in the last 10 days on Peruibe, Praia Grande and Itanhaem beaches in Sao Paulo state, said Thiago do Nascimento, a biologist at the Peruibe Aquarium.

Most were Magellan penguins migrating north from Argentina, Chile and the Falkland Islands in search of food in warmer waters.

Many are not finding it: Autopsies done on several birds revealed their stomachs were entirely empty - indicating they likely starved to death, Mr Nascimento said.

Scientists are investigating whether strong currents and colder-than-normal waters have hurt populations of the species that make up the penguins' diet, or whether human activity may be playing a role.

"Overfishing may have made the fish and squid scarcer," Mr Nascimento said.

He said it was common for penguins to swim north this time of year. Inevitably, some get lost along the way or die from hunger or exhaustion, and end up on the Brazilian coast far from home.

But not in such numbers - Mr Nascimento said about 100 to 150 live penguins show up on the beach in an average year, and only 10 or so are dead.

"What worries us this year," he said, "is the absurdly high number of penguins that have appeared dead in a short period of time."

The Food and Drug Administration is seriously considering whether to approve the first genetically engineered animal that people would eat — salmon that can grow at twice the normal rate.

AquaBounty, developer of the AquAdvantage Atlantic salmon, would sell fish eggs to fish farms, not salmon to supermarkets.

The developer of the salmon has been trying to get approval for a decade. But the company now seems to have submitted most or all of the data the F.D.A. needs to analyze whether the salmon are safe to eat, nutritionally equivalent to other salmon and safe for the environment, according to government and biotechnology industry officials. A public meeting to discuss the salmon may be held as early as this fall.

Some consumer and environmental groups are likely to raise objections to approval. Even within the F.D.A., there has been a debate about whether the salmon should be labeled as genetically engineered (genetically engineered crops are not labeled).

The salmon’s approval would help open a path for companies and academic scientists developing other genetically engineered animals, like cattle resistant to mad cow disease or pigs that could supply healthier bacon. Next in line behind the salmon for possible approval would probably be the “enviropig,” developed at a Canadian university, which has less phosphorus pollution in its manure.

The salmon was developed by a company called AquaBounty Technologies and would be raised in fish farms. It is an Atlantic salmon that contains a growth hormone gene from a Chinook salmon as well as a genetic on-switch from the ocean pout, a distant relative of the salmon.