The noise people make in the ocean from shipping, motorboats, seismic surveys, and pile-driving is known to interfere with the hearing and communication of marine animals. But showing how this interference directly affects the creatures’ survival has proven difficult. Now, via experiments in the lab and the wild, scientists have hard evidence that the sounds of motorboats help predators kill fish. Using recordings of boat noise, the scientists tested the hunting success rate of the predatory dusky dottyback fish (Pseudochromis fuscus) on one of its favorite prey, the Ambon damselfish (Pomacentrus amboinensis). Both species (shown in the photo above) are found in the Great Barrier Reef. Adult damselfish are residents on the reef, but their larvae develop in the open water, only settling on the coral as juveniles. At that stage, they suffer a high rate of mortality from new predators, including the dusky dottyback. The noise of motorboats passing 10 to 200 meters away significantly increases the young damselfishes’ death rate, the scientists report online today in Nature Communications. The scientists placed juvenile damselfish in the wild on isolated experimental reefs, and then either broadcast recordings of motorboats or the ambient sounds of their habitat. Only 27% of the juvenile damselfishes on the reefs with the motorboat noise survived during a 72-hour observation period, whereas 79% of the youngsters survived on the control reefs. Other experiments showed that the motorboat noise increases the metabolic rate of the juvenile fish, and makes them less likely to startle (the appropriate response) when attacked. The findings may help efforts to create marine quiet zones or regulations directing motorboats to avoid areas where juvenile fish are abundant, the scientists say.