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 — The federal government plans to use a protective zone east of Boston until early April to try to keep endangered whales safe.

The National Oceanic and Atmospheric Administration said the area will be in use through April 7. It’s designed to protect North Atlantic right whales, which number only about 400 and are vulnerable to collisions with ships.

NOAA said private citizens saw an aggregation of the whales from a Boston-area beach on March 23. The agency is asking mariners to route around the area or proceed at 10 knots or less.

NOAA also has a pair of protective areas off Nantucket that are in place until Friday.