A boat floating above a coral reef

Din from boats can interfere with the life lessons of fish living on coral reefs. Credit: Daniela Dirscherl/Getty

Ecology

Shh! Fish are learning

Boat noise disrupts memory formation in damselfish — and increases their risk of death as a result.

Sounds from noisy motorboats prevent fish from learning to recognize new predators.

Maud Ferrari at the University of Saskatchewan in Saskatoon, Canada, and her colleagues played recordings of either the natural sounds heard near a coral reef or the sounds of both a reef and a motorized dinghy to juvenile coral-reef damselfish (Pomacentrus amboinensis). At the same time, the researchers exposed the fish to two smells: that of an unfamiliar predator, and alarm odours produced by injured damselfish.

The next day, the team again exposed the fish to the predator’s odour. Fish that had heard only the reef noise responded with anti-predator behaviours, such as a reduction in foraging. But fish exposed to the noisy boat and reef sounds showed no such reaction, behaving the same way as naive fish that had never encountered the predator’s odour. They were also bolder and more active than the reef-noise group when released into a coral reef near Lizard Island in Australia — making them three times less likely to survive their first three days on the reef.