Of the three strikes during May, one involved a cruise ship hitting a sei whale and inadvertently dragging it into the Hudson River.
The attached dead animal was not discovered until the ship reached port.
The U.S. agency NOAA said another sei was found dead and attached to a container ship that was docking near Philadelphia three days later.
NOAA believes the whales may be following food sources unusually close to shore when they haplessly swim into shipping lanes.
Operators of whale-watching excursions in coastal waters off Boston report 20 to 30 whales are being spotted on every cruise — 10 times the usual number.
Photo: Florida Fish and Wildlife Conservation Commission