NANTUCKET, Mass. – The federal government is extending a protective zone off Massachusetts to try to keep a large group of endangered whales safe from collisions with boats.

The National Oceanic and Atmospheric Administration is applying the voluntary vessel speed restriction zone in an area 21 nautical miles south of Nantucket. A group of 17 right whales was seen in the area on Monday.

NOAA says the speed restriction zone will be in effect until Dec. 11. Mariners are asked to avoid the area or go through it at 10 knots or less.

Right whales number no more than 440 and have been hurt by heavy mortality and poor reproduction in recent years. The aggregation off Nantucket constitutes about 4 percent of the entire population of the animal, which was decimated by whaling.

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