The federal government is declaring the deaths of hundreds of seals off the New England coast this summer to be an “unusual mortality event.”

The National Oceanic and Atmospheric Administration has said tests indicate dead seals found in New England tested positive for avian flu and phocine distemper.

More than 240 seals have been found dead off the Maine coast in July and August, while more than 80 have been reported off New Hampshire and Massachusetts in those months.

NOAA said Friday it will investigate the “elevated strandings of harbor and grey seals in the Northeast attributed to disease.”

The agency says that declaring a marine mammal die-off as an “unusual mortality event” means the deaths will be prioritized for investigation and response.