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

BOSTON — The federal government is extending three protective zones designed to help endangered whales until late March.

The protective areas are intended to protect North Atlantic right whales from ship strikes, which can be fatal.

Two of the zones are based on aerial surveys by the National Oceanic and Atmospheric Administration that observed two separate aggregations of the whales 31 nautical miles south of Nantucket, Massachusetts, and 47 nautical miles southeast of Nantucket. NOAA said those protective areas are in effect through March 27.

Another protective area in effect through March 29 is based on the observation of right whales 18 nautical miles east of Boston.

The whales were observed earlier in the month. Mariners are asked to route around the three areas or transit through them at 10 knots or less.

There are only about 400 of the whales left in the world.