(CBS News) An increasing number of dolphins are washing up dead on East Coast shores this summer.
It's an upsetting trend, and the cause is still a mystery.
More than 120 dead dolphins have washed ashore between Virginia and New Jersey in the past two months. They're mainly bottlenose dolphins, and they are different ages and sizes.
"There's a number of things that cause animals to strand," said Maggie Mooney-Seus with the National Oceanic and Atmospheric Administration. "It could be biotoxins. It could be disease. It could be human interactions with fishing gear."
Mooney-Seus says the recent rash of dolphin deaths is very similar to an episode that happened in 1987, when more than 900 dolphins died. In that case, a bacterial infection was mostly to blame.
Virginia has seen the biggest spike this summer. Forty-two dolphins died in July, compared to 10 in July 2011 and 2012 combined.
"The concern here is that it's an elevated number of one species, so we are watching this very closely and collecting as much information as we can," Mooney-Seus said.
Sometimes the dolphins are found sick but alive. One was found trapped on a sandbar on New York's Long Island, but rescue worker Julika Wocial nursed it back to health.
"We still try to collect as much data information as we can from them, so we're hoping that there's still going to be a positive from those deaths," Wocial said.
Experts say the carcasses pose no potential health risk and the affected beaches are safe. One of the biggest issues has been cleanup. Each dolphin can weigh up to 500 pounds.