More than 75 North Atlantic right whales have been spotted in the shipping lanes south of Massachusetts, slowing vessels in the area, New England Aquarium said.The animals, which were likely feeding, prompted NOAA Fisheries to designate a voluntary slow zone urging mariners to slow down to 10 knots or less to prevent collisions.A group of more than 60 right whales was seen on April 23 about 55 miles south of Martha’s Vineyard. A second survey on April 28 saw 40 right whales, including 15 additional animals not seen during the first survey. Last month, about 30 right whales were seen in Cape Cod Bay near the canal. The North Atlantic right whale is critically endangered, with an estimated 370 animals remaining, including about 70 reproductively active females, and protected under the federal Endangered Species Act and the Marine Mammal Protection Act. That designation legally prohibits boats and aircraft from coming within 500 yards of them. It also restricts vessel speeds in designated areas, including Cape Cod waters.The right whale’s greatest threats to survival are being struck by a vessel or becoming entangled in rope.The right whale is the official marine mammal of Massachusetts.Video: Whales seen off Cape Cod