NANTUCKET, Mass. — The federal government has extended protections designed to keep rare whales safe off New England until Oct. 20.

The National Oceanic and Atmospheric Administration is asking mariners to go slowly through an area south of Nantucket or avoid it completely.

NOAA started the protections after an Aug. 31 sighting of a group of North Atlantic right whales.

The right whales number only about 400 and they are vulnerable to ship collisions and entanglement in fishing gear. An aerial survey found an aggregation of whales again on Oct. 4.

The slow zone is located off of southern New England and east of Long Island, New York.