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What’s killing the East Coast dolphins?

The carcasses of dozens of the marine mammals, seven times more than normal, have been washing up on beaches this summer, and scientists are struggling for answers to the die-off.

In Virginia alone, at least 164 dead dolphins have been found this year, said Joan M. Barns, public relations manager for the Virginia Aquarium in Virginia Beach. Almost half of those, 78, have washed ashore in August, she said.

As of Tuesday, federal authorities say, they have recorded 228 dolphin deaths this year from New York to Virginia. In all of 2012, 111 deaths were recorded.

The National Oceanic and Atmospheric Administration has issued an Unusual Mortality Event in response to the deaths. The declaration brings special federal attention to deaths as something that serves as an indicator of ocean health and may give “insight into larger environmental issues which may also have implications for human health and welfare,” according to NOAA’s website.

The current declaration for the mid-Atlantic bottlenose dolphins is one of 60 Unusual Mortality Events the agency has issued since they were established under the Marine Mammal Protection Act in 1991. Causes, including infections, biotoxins, human intervention and malnutrition, have been determined for the 29 of those cases.

Early speculation into the latest deaths, which have spiked this month, is focused on an infection.