A dolphin die-off in the Mid-Atlantic region is hitting Virginia hardest.
Nearly 50 dolphins were found dead or dying in Virginia in July -- seven times the normal rate for that month -- and the pace is picking up.
"August is looking to be significantly worse," said Mark Swingle, director of research and conservation for the Virginia Aquarium & Marine Science Center in Virginia Beach.
The nonprofit aquarium is home to Virginia's sole program for responding to stranded dolphins, whales and sea turtles.
Bottlenose dolphins, intelligent and charismatic mammals loved by the public, are dying at abnormally high rates this summer from New York to Virginia -- 156 animals from July 1 through Monday. The average for a full year in that region is 99.
Most of the dolphins washed up dead. Some died soon after being found or were so near death they had to be euthanized. None has survived to be returned to the wild.
The National Oceanic and Atmospheric Administration last week declared the deaths "an unusual mortality event" -- a declaration that frees up extra scientific expertise to investigate the case.
In Virginia, about a half-dozen dolphins normally wash up in July, and an additional half-dozen in August. Last month, there were 48, and this month there were 35 through Monday, officials said.
Such a large number before mid-August "is not a good sign," Swingle said.
Virginia's 83 deaths lead among the affected states, far surpassing second-place New Jersey's 39.
The cause of the deaths is a mystery. It could be that some disease is working its way through the dolphin population.
That's what happened in 1987, the last time the East Coast experienced a similar die-off. More than 740 dolphins succumbed from New Jersey to Florida. More than 200 died in Virginia, the most of any state along the coast.
Experts linked the deaths to a virus found in some marine mammals, morbillivirus. Toxins from harmful algae may have contributed to some deaths.
Preliminary tests indicate a few of the dolphins that died this summer suffered from morbillivirus, but experts say it's too early to say that's causing all the deaths.
It could be that some other problem -- a toxic-chemical spill, say, or a release of toxins by algae -- weakened dolphins' immune systems, making them vulnerable to a disease they normally would ward off.
Morbillivirus is similar to measles in people, said Mendy Garron, the marine mammal stranding coordinator for NOAA's Maine-to-Virginia region.
"The measles can potentially kill someone if their immune system is suppressed," Garron said. "It's kind of that same concept."
The investigation of the deaths could take months or even years, officials say. That means no one can help the animals that are dying now. But the investigation might shed light on similar events in the future.
It's not clear why most of the stricken dolphins are washing up in Virginia.
It could be that some local pollution problem is hurting the dolphins, experts said. Or it could be something as simple as currents carrying bodies here.
There is another possible, and simple, explanation: Of all the affected states, Virginia has the most dolphins. Thousands of the mammals live and migrate along the East Coast, and their Virginia numbers peak in summer.
"Since there are more animals in Virginia, obviously we are going to see more animals affected," Swingle said.
People love dolphins, and they are concerned about the deaths. But Swingle said there is another reason to pay attention.
"Marine mammals are mammals like you and I. They get some of the same diseases that we get. They are sort of sentinels for us in the water. When they are having trouble ... we certainly want to know what's going on and understand it better."
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