Motorboat noise causes clownfish to hide and skip meals, study finds

Motorboat noise causes clownfish to hide, skip meals and attack their neighbours, research has found.

An international team of scientists studied 40 pairs of the fish – depicted in the film Finding Nemo – on reefs around Moorea in French Polynesia.

The fish were exposed to recordings of natural reef sounds or motorboat noise for up to two days.

Motorboat noise caused clownfish to hide in the protective tentacles of their host anemone, become more aggressive towards domino damselfish also living there, and move less into open water to feed.

Researchers from France, Chile and the UK also found the fish were unable to respond appropriately to a second stressor, putting them at greater potential risk from predators and climate change.

The study, published in the journal Environmental Pollution, found noise-exposed fish had elevated levels of the stress hormone cortisol and the reproductive hormones testosterone and 11-ketotestosterone.

Associate Professor Suzanne Mills, at the Ecole Pratique des Hautes Etudes PSL Universite Paris, said: “The high cortisol levels after two days of exposure suggest that clownfish become chronically stressed by motorboat noise.

“This compromises the stress response system leaving clownfish unable to mount appropriate responses to further stressful events.

“If these stressful events include a predator, motorboat noise could have grave implications.”

The scientists found the clownfish used more energy to aggressively defend their territory during motorboat noise.

But the fish hid more and moved less to feed, even after the noise had gone away, which could affect their growth and survival.

It is hoped that further research could predict the duration or interval of motorboat noise exposure that would allow the fish to return to normal behaviour.

Steve Simpson, professor of Marine Biology & Global Change at the University of Exeter, said: “Hormonal responses to different boat engines, propeller designs and spatial management of boating activities can be compared to reduce the impact of this globally prevalent pollutant.

“Hormonal responses are currently an underemployed tool for managing the noise of the 100,000s of motorboats used around the world.”