A rule requiring ships to travel at reduced speeds to protect endangered North Atlantic right whales in certain areas along the East Coast has been made permanent, the National Oceanic and Atmospheric Administration has announced.

The entrances to the Delaware Bay, Chesapeake Bay and New York Harbor are among the areas affected.

NOAA said the rule, which was put in place in 2008 and set to expire this month, had proven effective in protecting the right whale, of which only about 450 to 500 remain.

Under the rule, all vessels 65 feet or longer must travel at 10 knots or less in the specified locations. The rule is in effect from Nov. 1 through April 30 in the Northeast and from Nov. 15 through April 15 along a stretch of the Georgia-Florida coast.

Ship strikes are the leading cause of nonnatural death for the whales, which can grow up to 60 feet and weigh 100 tons, NOAA said.