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

NANTUCKET, Mass. — The federal government is extending a protective zone designed to keep rare whales safe until close to the end of the month.

The National Oceanic and Atmospheric Administration said the area is south of Nantucket, where a large group of North Atlantic right whales was spotted earlier this month. The agency said the protective zone will be in effect until Feb. 24.

NOAA is asking mariners to route around the area or transit through it at 10 knots of less. There are only about 400 of the whales left in the world, and about one-eighth of the entire population was recently seen in the area.

Watch: This right whale gets partially disentangled off Cape Cod