A spotter bangs three times on the boat's cabin roof, signaling the captain to cut the throttle - now. In the foggy gray of Cape Cod Bay, the reason for the abrupt stop soon becomes apparent: The research vessel is surrounded by rare North Atlantic right whales, their glossy black heads bobbing just above the surface as they feed on plankton slicks. Ship strikes are the top human-related cause of death for these mammals, which are in danger even from this vessel, a slow-moving research boat called the Shearwater. But new technology could soon help safeguard the whales by using sound, not sight, to track the creatures' movements.