In this March 28, 2018, file photo, a North Atlantic right whale feeds on the surface of Cape Cod bay off the coast of Plymouth, Massachusetts. Credit: Michael Dwyer | AP

BOSTON — Federal ocean managers are asking mariners to slow down east of Boston because of a new sighting of rare whales in the area.

Private citizens found an aggregation of North Atlantic right whales in the area. The National Oceanic and Atmospheric Administration said it is asking mariners to go around the area or travel through it at 10 knots or less until April 24.

The citizens saw the group of whales on April 9. Right whales number only about 400 and are one of the rarest large ocean animals.

The whales are moving along the East Coast at the moment and NOAA is asking boaters and fishermen to take steps to avoid harming them.