Abstract

Underwater ocean noise from human maritime activities has increased significantly over the last 50 years.^1,2 The dominant source of low-frequency noise (20–200 Hertz) is from the engines and propellers of large ships.^1-3 Ship noise frequencies overlap with baleen whale (Mysticeti) acoustic signals, masking whale communication sounds.^4,5 Baleen whales rely on low-frequency, long-wavelength acoustic signals to communicate over large distances. Reported whale responses to elevated underwater noise include: habitat displacement, behavioral changes, and alterations in the intensity, frequency, and intervals of calls.^4-6 However, it has been unknown if chronic exposure to elevated underwater noise results in measurable physiological responses in individuals and if there are potential consequences for population viability.⁷ The events of 11 September 2001 (9/11) resulted in an unanticipated experiment on the effects of ocean noise on western North Atlantic right whales (Eubalaena glacialis) in the Bay of Fundy, Canada. We compared the sound pressure level (SPL) and frequency spectrum from hydrophone recordings taken on two days before 9/11 with two days immediately following 9/11. Acoustic data showed a 6 dB decrease in underwater noise below 150 Hz related to reduced ship traffic following 9/11. In a concurrent study, we compared levels of adrenal glucocorticoid (GC) metabolites measured by radioimmunoassay in right whale fecal samples before (n = 114) and after 11 September (n = 30) for the years 2001–2005.⁸ The only year in which there was a significant decrease in fecal GCs after 11 September was 2001 with a significant effect of year and period (Kruskall-Wallis X² = 29.6889, df = 4, P < 0.0001). Consistent surveys throughout the study period revealed no other known factors that could explain this difference besides the decrease in ship traffic and reduced underwater noise following 9/11. This is the first evidence that exposure to underwater noise from large ships is associated with a measure of chronic stress in free-ranging whales, and may have implications for baleen whales in heavy ship traffic areas and for recovery of this endangered right whale population

Acknowledgements

The authors are grateful to the Office of Naval Research, NOAA Fisheries, and the Northeast Consortium for financial support for this project. Our thanks to the New England Aquarium right whale team and other researchers who collected samples forthe stress hormone study; Philip Hamilton for right whale data discussions; Jackie Ciano, Stephanie Martin, and Cynthia Thomas for assistance with acoustic recordings; Angelia Vanderlaan and Chris Taggert for supplying ship traffic data for the Bay of Fundy; and Brooke Wikgren for graphics. This research was conducted under permits from Fisheries & Oceans, Canada, and Scientific Research Permits under the Canadian Species at Risk Act.

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