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Dolphin die-off tied to Gulf oil spill, other factors, study suggests

By Kevin Spear, The Orlando Sentinel –

ORLANDO, Fla. — Bottlenose dolphins in the Gulf of Mexico washed up dead along the shores of four states early last year in one of the worst die-offs on record in the region.

Had they been poisoned by the oil that gushed for weeks into the northern Gulf from BP’s stricken deep-sea well less than a year earlier?

Finding evidence of that would be very difficult, if not impossible, said Graham Worthy, a University of Central Florida biology professor who has worked with marine mammals for more than 30 years.

But that doesn’t mean the nation’s biggest offshore spill of crude oil didn’t play a key role in the deaths of the 186 bottlenose dolphins recovered from Gulf waters from January through April last year. Many of the animals were in horrible shape, apparently starving and weakened before death, Worthy said, suggesting that their health and the availability of food — in their case, fish — had been significantly depleted in the months after the BP spill.

“Clearly something was hammering them,” Worthy said of the dead dolphins found on Florida’s Panhandle beaches and along the coasts of Alabama, Mississippi and Louisiana. “It was clear that it wasn’t likely to be a simple cause-and-effect issue but, rather, that there were likely several factors coming together — a perfect storm of impacts — and we felt that we could help try to solve this mystery.”

The examination and assessment of the environmental damage caused by the BP spill — a legal and scientific process that will include the plight of the dolphins and a wide range of other plant and wildlife species — will probably continue for years, said Ben Sherman, a spokesman for the National Oceanic and Atmospheric Administration.

That there is much difficult work ahead was underscored by the recent dolphin study from Worthy and a team of other biologists at Gulf of Mexico research institutions.

Their probe into the 186 dolphin deaths — five to 10 times as many as ordinarily expected in a four-month period — reinforced the thinking of many scientists that most of the environmental harm caused by the 2010 oil spill wasn’t in obvious forms, such as heavily oiled birds, but rather in obscure and probably poorly understood cascades of ecosystem disruptions.

The dolphins, for example, may have been doomed by the confluence of spilled oil, cold waters and poor health.

Worthy and his co-researchers found that nearly half of the dolphins that perished had just been born or were about to be born. They were far too young to have encountered either the BP spill’s floating slicks or its submerged plumes of crude oil, though they might have been conceived during the spill, which began April 20, 2010, and continued for more than 85 days.

Unusually large numbers of dolphins also died in the months before and after the January-through-April period chosen by the researchers; what stands out about those four months is the high percentage of deaths among very young dolphins.

Worthy said data gathered from examinations of the dead dolphins show many had been infected by brucellosis, a bacterial disease known for causing livestock to have abortions and suspected of triggering similar results in seals and other marine mammals.

The disease is ordinarily present in the dolphins’ environment, Worthy said, but in this case their immune systems might have been too weak to fight it. Other researchers have linked poor disease resistance to the oil spill.

Last summer, NOAA biologists captured and examined 32 dolphins in Louisiana’s Barataria Bay, one of the mostly heavily oiled spots along the Gulf Coast. They discovered that many of the animals were underweight, anemic, suffering from low blood sugar and showing symptoms of liver and lung diseases. Nearly half also had low levels of the hormones vital to the dolphins’ metabolism and to their ability to handle stress and resist disease.

The agency is still investigating the deaths of more than 720 dolphins since 2010. About half have occurred along the Louisiana coast, while about 10 percent were recorded on Florida shores.

Cold weather is another hazard for the Gulf of Mexico’s bottlenose dolphins, but it’s one they generally can survive.

Worthy said the dolphins were probably hit by cold weather in early 2010 and then the BP spill that spring and summer; as a result, he said, the animals were in poor shape when yet another cold snap and influx of cold river water hit the Gulf early in 2011.

Ruth Carmichael, a marine scientist at Dauphin Island Sea Lab in Alabama and lead author of the dolphin study, said the animals were already in serious trouble early last year when their carcasses began to come ashore.

“When we put the pieces together, it appears that the dolphins were likely weakened by depleted food resources, bacteria or other factors as a result of the 2010 cold winter or oil spill,” Carmichael said.

Worthy says more analysis should be done, including sophisticated laboratory work on the tissues of the dead dolphins to determine whether they lived near shore or far out in the Gulf, where they might have been exposed to few of the spill’s effects.

“Maybe we are off-base in our findings,” he said, “but we don’t think that’s the case.”

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