New Publication : 8 April 2020 (Mills et al)

Boat noise sends Nemo rogue: raging hormones and bad behaviour
8 April 2020 | Contact: SUZANNE MILLS| Environmental Pollution

Working on the reefs around Moorea in French Polynesia, the scientists exposed 40 pairs of clownfish 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, moving less into open water to feed but being more aggressive towards domino damselfish that also reside in the anemone. Noise-exposed fish had elevated levels of the stress hormone cortisol and the reproductive hormones testosterone and 11-ketotestosterone, which corresponded with observed behavioural changes.

Lead author, Associate Professor Suzanne Mills at the École Pratique des Hautes Études (EPHE) PSL Université Paris, CRIOBE, France, 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.”

Ricardo Beldade, Associate Professor at the Pontificia Universidad Católica de Chile, and previously with the Centre National de la Recherche Scientifique (CNRS) at CRIOBE, France said, “Clownfish defended their anemone territory aggressively during motorboat noise, which requires more energy. However, as the fish hid more and moved less to feed, even after the motorboat noise had passed, they may be unable to compensate through more foraging, with potentially detrimental impacts on growth and even survival.”

“Experiments that consider behaviour of wild animals in natural conditions—as we have done in this study—are crucial if we are to understand fully the impact of anthropogenic noise. Our results highlight that behavioural changes caused by anthropogenic noise are likely underpinned by alterations in the stress response (cortisol) and certain steroid hormones,” added Professor Andy Radford, University of Bristol.

Dr Sophie Nedelec, University of Exeter, said, “Now we know that hormonal responses are the mechanisms driving behavioural changes to motorboat noise, they can be a useful tool in regulation. We might be able to predict the duration and/or interval times of motorboat noise exposure that allow individuals to return to normal behaviour.”

“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,” added Professor Steve Simpson, University of Exeter.

Mills summarised, “Our new findings highlight the need to control man-made noise in marine protected habitats.”

© Frederic Zuberer

Mills, S.C., Beldade, R., Henry, L., Laverty, D., Nedelec, S.L., Simpson, S.D., & Radford, A.N. 2020. Hormonal and behavioural effects of motorboat noise on wild coral reef fish. Environmental Pollution.

Suzanne MILLS | Polynésie française | +56 9 5799 7194


  • Estación Costera de Investigaciones Marinas and Center for Advanced Studies in Ecology and Biodiversity, Las Cruces, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, CP 6513677, Chile
  • Ulster University, School of Geography and Environmental Sciences, Cromore Rd, Coleraine BT52 1SA, Londonderry, Northern Ireland.
  • School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol, BS8 1TQ, UK
  • Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, EX4 4PS, UK