A mysterious rise in deaths of bottlenose dolphins this year has left scientists and officials in multiple states searching for answers. As of last Thursday, Reuters reports, more than 120 dead dolphins had been discovered across the East Coast, and carcasses continue to wash up on Atlantic shores.

So far most of the deaths have occurred in Virginia around the southern areas of the Chesapeake Bay. According to the Virginia Aquarium and Marine Science Center, the average number of dolphin strandings for July is seven; This year, the aquarium has responded to 44 deaths in July alone. Just yesterday, as Richmond's local CBS affiliate WTVR reported, the aquarium confirmed that an additional 13 dead dolphins were found over the weekend. WTVR reports that two scientists from the Smithsonian Institution have been dispatched to assist with an investigation that has so far produced no definitive answers.

In 1987 and 1988, more than 700 dolphins were killed by bacterial and viral infections

This year's rash of deaths hasn't been seen on a similar level since 1987 and 1988, when more than 700 dolphins were found dead on the Atlantic seaboard over an 18 month period. Those deaths were found to be caused by bacterial and viral infections, leading some researchers to speculate that a similar outbreak could be the cause of this year's spike in dolphin fatalities.

Federal investigators are also participating in the search for answers, but have not nailed down a single cause. "There's a number of things that cause animals to strand," NOAA's Maggie Mooney-Seus told CBS News. "It could be biotoxins. It could be disease. It could be human interactions with fishing gear."

"It's absolutely alarming," a Virginia Aquarium and Marine Science Center researcher told Reuters. "This is really frightening because these animals are sentinels of ocean health."