SAN FRANCISCO - Four gray whales have been found dead in just over a week.

In the past eight days, whale carcasses have been washing up on beaches in the Bay Area. One whale's death was linked to injuries caused by a ship. Authorities have been trying to determine the cause of death for the other three whales.

These deaths have been ruled an unusual mortality event, according to the National Oceanic and Atmospheric Administration. This means the deaths show an "unusual" and "significant" die-off of the gray whale population.

While they're not endangered yet, gray whale numbers are rapidly declining. According to NOAA, one in four gray whales has died since the 2016 population assessment.

Authorities say that teams are currently monitoring gray whales in the Bay Area.