This March 11, 2021, photo shows a North Atlantic right whale mother and calf in waters near Cumberland Island, Georgia. Credit: Courtesy of Georgia Department of Natural Resources / AP

BOSTON — A group of rare whales has been spotted east of Boston, prompting the federal government to urge caution among boaters.

The whales are North Atlantic right whales, which number only about 360 in the world. The National Oceanic and Atmospheric Administration said it is asking mariners to route around the area or transit through it at 10 knots or less until April 23.

The whales were spotted on April 8. Right whales are on the move this time of year. The animals are often seen off Massachusetts as they head north.

The whales are vulnerable to collisions with ships and entanglement in commercial fishing gear.

NOAA has deployed similar “slow zones” south of Nantucket and southeast of Chatham recently.