How did the COVID-19 pandemic affect underwater sound?

The coronavirus (COVID-19) pandemic caused significant impacts around the globe. By April 2020, half of the world’s population was under some form of lockdown, with many individuals ordered to stay at home to some degree. Many unexpected, trickle-down effects occurred, including changes to terrestrial and underwater soundscapes. Shelter-in-place orders and non-essential travel bans caused unprecedented slowdowns in industrial, transportation, and recreational activities (“anthropause”), which led to less anthropogenic noise from sources, such as construction, buses, cars, ships, and aircraft. Decreases in human activities may have led to noticeable reductions in the vibrations (seismic noise) of the Earth’s upper crust in and around cities [1]Gibney, E. (2020). Coronavirus Lockdowns Have Changed the Way Earth Moves. Nature. 580 (7802): 176–77. https://doi.org/10.1038/d41586-020-00965-x.

As part of health and safety measures related to the pandemic, commercial, research, and other types of large vessel traffic were reduced or completely halted. Vessel traffic decreased 44% across the global ocean, with major changes in traffic density found in coastal areas and in the northern hemisphere. Large passenger vessels were most affected, especially in tourist hot spots such as the Caribbean and Mediterranean[2]March, D., K. Metcalfe, J. Tintoré, and B.J. Godley. (2021). Tracking the Global Reduction of Marine Traffic during the COVID-19 Pandemic. Nature Communications. 12 (1): 2415. https://doi.org/10.1038/s41467-021-22423-6.. With a global reduction in vessel traffic, a corresponding reduction in underwater noise was observed in many locations. Shipping noise is a main contributor to the lower frequencies of the marine soundscape up to 500 Hz.

Map showing a difference plot of annual noise source energy (63 Hz 1/3 octave band) emitted from ships in 2020 and 2019 (energy emissions are given in units of megajoules per grid cell). During the COVID-19 pandemic, underwater noise emissions significantly decreased along major shipping routes (dark blue on map). Figure 4 from Jalkanen, J., L. Johansson, M.H. Andersson, E. Majamäki, and P. Sigray. 2022. Underwater Noise Emissions from Ships during 2014–2020. Environmental Pollution. 311: 119766. Open Access under Creative Commons Attribution 4.0 International (CC BY 4.0)

Thomson and Barclay (2020) reviewed underwater acoustics data recorded by four, bottom-mounted hydrophone stations that are part of Ocean Network Canada’s (ONC) VENUS and NEPTUNE ocean observatories. Comparing the weekly rate of change in ambient noise in the first quarter of 2020 to the last quarter of 2018 and all four quarters of 2019, Barclay and Thompson found that the median acoustic power at 100 Hz was lower in 2020 for three of the four hydrophone stations. Data from the two VENUS observatory hydrophones near the shipping channels off Vancouver Island showed a 4 to 5 decibel (dB) reduction during the first three months of 2020 (figure below), which the scientists attributed to early coronavirus impacts on trade (shipping) between Asia and the Port of Vancouver. At the Endeavour node of the NEPTUNE observatory, an average reduction of 1.5 dB between 2019 and 2020 in mean weekly noise power spectral density at 100 Hz was also observed [3]Thomson, D. J. M., & Barclay, D. R. (2020). Real-time observations of the impact of COVID-19 on underwater noise. The Journal of the Acoustical Society of America, 147(5), 3390–3396. https://doi.org/10.1121/10.0001271.

Yearly time-series of median (solid line) and 1st percentile (dashed-dotted line) weekly power spectral density at 100 Hz recorded at the Endeavor node hydrophone station for 2017 (black), 2018 (navy), 2019 (blue), and 2020 (red). Yearly time-series of median (solid line) and 1st percentile (dashed-dotted line) weekly power spectral density at 100 Hz recorded at the Endeavor node hydrophone station for 2017 (black), 2018 (navy), 2019 (blue), and 2020 (red). Reproduced from – Thomson, D.J.M. and D.R. Barclay. (2020). Real-time observations of the impact of COVID-19 on underwater noise The Journal of the Acoustical Society of America, 147, 3390–3396. https://doi.org/10.1121/10.0001271, with the permission of the Acoustical Society of America.

Other locations also noted decreased sound pressure levels due to reduced large vessel activity. A decrease of more than 1.0 dB in the 63-Hz one-third octave band was observed in Monterey Bay Maine Sanctuary, California, U.S.A. [4]Ryan, J. P., Joseph, J. E., Margolina, T., Hatch, L. T., Azzara, A., Reyes, A., Southall, B. L., DeVogelaere, A., Peavey Reeves, L. E., Zhang, Y., Cline, D. E., Jones, B., McGill, P., Baumann-Pickering, S., & Stimpert, A. K. (2021). Reduction of low-frequency vessel noise in Monterey Bay National Marine Sanctuary during the COVID-19 pandemic. Frontiers in Marine Science, 8, 656566. https://doi.org/10.3389/fmars.2021.656566; a 1.2 dB decrease was noted for low frequencies (10Hz-1kHz) in the German Baltic Sea[5]Basan, F., Fischer, J.-G., & Kühnel, D. (2021). Soundscapes in the German Baltic Sea Before and During the Covid-19 Pandemic. Frontiers in Marine Science, 8, 689860. https://doi.org/10.3389/fmars.2021.689860; a 7.0 dB decrease in the 63-125 Hz one-third octave band occurred in the Skagerrak Strait between Norway and Sweden[6]De Clippele, L. H., & Risch, D. (2021). Measuring sound at a cold-water coral reef to assess the impact of COVID-19 on noise pollution. Frontiers in Marine Science, 8, 674702. https://doi.org/10.3389/fmars.2021.674702.; and a 3.98 dB decrease in the 111-140 Hz one-third octave band was observed in the waters of the northern Bahamas[7]Dunn, C., Theriault, J., Hickmott, L., & Claridge, D. (2021). Slower ship speed in the Bahamas due to COVID-19 produces a dramatic reduction in ocean sound levels. Frontiers in Marine Science, 8, 673565. https://doi.org/10.3389/fmars.2021.673565.. In the Bahamas, a reduction in ship speed, in addition to reduced vessel presence overall, contributed to a decrease in observed sound pressure levels.

Reduced sound levels were even recorded in the deep ocean during the first half of 2020. Measurements from multiple Comprehensive Test Ban Treaty CTBT hydroacoustic stations showed reductions from 1-3 dB in the frequency range from 10-100 Hz[8]Robinson, S., Harris, P., Cheong, S.-H., Wang, L., Livina, V., Haralabus, G., Zampolli, M., & Nielsen, P. (2023). Impact of the COVID-19 pandemic on levels of deep-ocean acoustic noise. Scientific Reports, 13(1), 4631. https://doi.org/10.1038/s41598-023-31376-3.. Ships are not the only sound source at frequencies below 100 Hz, however, and reduced geophysical activities along the coasts of Africa and South America may have also contributed to the observed sound level reductions.

Underwater sound associated with recreational boats was also reduced in some locations. Near the Bas-du-Fort marina in Guadeloupe, French West Indies, a significantly lower number of motorboats was recorded during the peak of the first COVID lockdown in the region (April-May 2020). When human activities resumed at the end of May 2020, and boat traffic increased, underwater sound increased to 6 dB above ambient noise levels[9]Bertucci, F., Lecchini, D., Greeven, C., Brooker, R. M., Minier, L., Cordonnier, S., René-Trouillefou, M., & Parmentier, E. (2021). Changes to an urban marina soundscape associated with COVID-19 lockdown in Guadeloupe. Environmental Pollution, 289, 117898. https://doi.org/10.1016/j.envpol.2021.117898. .

All vessel activity in the Hauraki Gulf Marine Park (HGMP) a 4,000 km2 area in the waters off and around Auckland, New Zealand, abruptly declined during a very strict period of lockdown in March 2020. All recreational boating was banned from the area for seven weeks. Acoustic recordings within the Hauraki Gulf showed ambient sound levels in normally busy channels decreased rapidly[10]Pine, M. K., Wilson, L., Jeffs, A. G., McWhinnie, L., Juanes, F., Scuderi, A., & Radford, C. A. (2021). A Gulf in lockdown: How an enforced ban on recreational vessels increased dolphin and fish communication ranges. Global Change Biology, 27(19), 4839–4848. https://doi.org/10.1111/gcb.15798.. Median sound pressure levels decreased by 8-10 dB on the first day of lockdown (March 26, 2020). In one channel in the Hauraki Gulf, which is typically busy with small boats, on the first day of lockdown, underwater sounds associated with recreational boating were recorded only 34% of the time and subsequently dropped to 8% after five days (figure below).

Spectrograms for vessel noise and weather-related noise, before and during a COVID-19 lockdown within the Rangitoto Channel, Hauraki Gulf Marine Park, New Zealand. The lockdown had an immediate effect on underwater sound in the Marine Park, particularly at frequencies below 1 kHz. Image used with permission, figure 2 from Pine, M. K., Wilson, L., Jeffs, A. G., McWhinnie, L., Juanes, F., Scuderi, A., & Radford, C. A. (2021). A Gulf in lockdown: How an enforced ban on recreational vessels increased dolphin and fish communication ranges. Global Change Biology, 27(19), 4839–4848. https://doi.org/10.1111/gcb.15798

The COVID-19 pandemic provided a unique opportunity to study underwater soundscapes without anthropogenic contributions and quantify relationships between sound sources and soundscapes, especially in biologically important habitats. Potential impacts were not homogeneous across the globe, however, as changes in response to the COVID-19 pandemic varied spatially and temporally. Local environmental factors, as well as their type and amount of anthropogenic noise that was typical before the pandemic, will also factor into potential effects.

Scientists continue to investigate the potential effects, if any, of underwater soundscape changes associated with COVID-19 on local marine life. Observations may inform conservation and management activities for various marine habitats and species. For example, scientists calculated that the reduction in small vessel sounds in New Zealand significantly increased the communication range for bottlenose dolphins and bigeyes fish[11]Pine, M. K., Wilson, L., Jeffs, A. G., McWhinnie, L., Juanes, F., Scuderi, A., & Radford, C. A. (2021). A Gulf in lockdown: How an enforced ban on recreational vessels increased dolphin and fish communication ranges. Global Change Biology, 27(19), 4839–4848. https://doi.org/10.1111/gcb.15798..

In Dolphin Bay Bocas del Toro, Panama, acoustic detections of dolphins increased twofold during lockdown. Dolphin whistles had higher minimum and maximum frequencies relative to pre-lockdown observations and were longer in duration. Whistle repertoires were also more diverse during lockdown (relative to pre-lockdown)[12]Gagne, E., Perez-Ortega, B., Hendry, A. P., Melo-Santos, G., Walmsley, S. F., Rege-Colt, M., Austin, M., & May-Collado, L. J. (2022). Dolphin communication during widespread systematic noise reduction-a natural experiment amid COVID-19 lockdowns. Frontiers in Remote Sensing, 3, 934608. https://doi.org/10.3389/frsen.2022.934608.. Changes in whistle modulation may indicate a change in dolphin behavioral activities during periods of COVID restrictions, and the presence of diverse whistle signatures may indicate an increase in dolphin presence.

Additional research is needed to fully understand how these responses, as well as other observations for other species in other locations, compared to pre and/or post-COVID environments.

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References

  • Dahl, P. H., Dall’Osto, D. R., & Harrington, M. J. (2021). Trends in low-frequency underwater noise off the Oregon coast and impacts of COVID-19 pandemic. The Journal of the Acoustical Society of America, 149(6), 4073–4077. https://doi.org/10.1121/10.0005192.
  • Laute, A., Grove, T., Rasmussen, M., Smith, A., Loisa, O., & Fournet, M. (2022). Impact of whale-watching vessels on humpback whale calling behavior on an Icelandic foraging ground during the Covid-19 pandemic. Marine Ecology Progress Series, 701, 159–173. https://doi.org/10.3354/meps14202.
  • Longden, E. G., Gillespie, D., Mann, D. A., McHugh, K. A., Rycyk, A. M., Wells, R. S., & Tyack, P. L. (2022). Comparison of the marine soundscape before and during the COVID-19 pandemic in dolphin habitat in Sarasota Bay, FL. The Journal of the Acoustical Society of America, 152(6), 3170–3185. https://doi.org/10.1121/10.0015366.
  • Miksis-Olds, J. L., Martin, B. S., Lowell, K., Verlinden, C., & Heaney, K. D. (2022). Minimal COVID-19 quieting measured in the deep offshore waters of the U.S. Outer Continental Shelf. JASA Express Letters, 2(9), 090801. https://doi.org/10.1121/10.0013999.
  • Smith, K. B., Leary, P., Deal, T., Joseph, J., Ryan, J., Miller, C., Dawe, C., & Cray, B. (2022). Acoustic vector sensor analysis of the Monterey Bay region soundscape and the impact of COVID-19. The Journal of the Acoustical Society of America, 151(4), 2507–2520. https://doi.org/10.1121/10.0010162.

Cited References

Cited References
⇡1 Gibney, E. (2020). Coronavirus Lockdowns Have Changed the Way Earth Moves. Nature. 580 (7802): 176–77. https://doi.org/10.1038/d41586-020-00965-x
⇡2 March, D., K. Metcalfe, J. Tintoré, and B.J. Godley. (2021). Tracking the Global Reduction of Marine Traffic during the COVID-19 Pandemic. Nature Communications. 12 (1): 2415. https://doi.org/10.1038/s41467-021-22423-6.
⇡3 Thomson, D. J. M., & Barclay, D. R. (2020). Real-time observations of the impact of COVID-19 on underwater noise. The Journal of the Acoustical Society of America, 147(5), 3390–3396. https://doi.org/10.1121/10.0001271
⇡4 Ryan, J. P., Joseph, J. E., Margolina, T., Hatch, L. T., Azzara, A., Reyes, A., Southall, B. L., DeVogelaere, A., Peavey Reeves, L. E., Zhang, Y., Cline, D. E., Jones, B., McGill, P., Baumann-Pickering, S., & Stimpert, A. K. (2021). Reduction of low-frequency vessel noise in Monterey Bay National Marine Sanctuary during the COVID-19 pandemic. Frontiers in Marine Science, 8, 656566. https://doi.org/10.3389/fmars.2021.656566
⇡5 Basan, F., Fischer, J.-G., & Kühnel, D. (2021). Soundscapes in the German Baltic Sea Before and During the Covid-19 Pandemic. Frontiers in Marine Science, 8, 689860. https://doi.org/10.3389/fmars.2021.689860
⇡6 De Clippele, L. H., & Risch, D. (2021). Measuring sound at a cold-water coral reef to assess the impact of COVID-19 on noise pollution. Frontiers in Marine Science, 8, 674702. https://doi.org/10.3389/fmars.2021.674702.
⇡7 Dunn, C., Theriault, J., Hickmott, L., & Claridge, D. (2021). Slower ship speed in the Bahamas due to COVID-19 produces a dramatic reduction in ocean sound levels. Frontiers in Marine Science, 8, 673565. https://doi.org/10.3389/fmars.2021.673565
⇡8 Robinson, S., Harris, P., Cheong, S.-H., Wang, L., Livina, V., Haralabus, G., Zampolli, M., & Nielsen, P. (2023). Impact of the COVID-19 pandemic on levels of deep-ocean acoustic noise. Scientific Reports, 13(1), 4631. https://doi.org/10.1038/s41598-023-31376-3.
⇡9 Bertucci, F., Lecchini, D., Greeven, C., Brooker, R. M., Minier, L., Cordonnier, S., René-Trouillefou, M., & Parmentier, E. (2021). Changes to an urban marina soundscape associated with COVID-19 lockdown in Guadeloupe. Environmental Pollution, 289, 117898. https://doi.org/10.1016/j.envpol.2021.117898.
⇡10 Pine, M. K., Wilson, L., Jeffs, A. G., McWhinnie, L., Juanes, F., Scuderi, A., & Radford, C. A. (2021). A Gulf in lockdown: How an enforced ban on recreational vessels increased dolphin and fish communication ranges. Global Change Biology, 27(19), 4839–4848. https://doi.org/10.1111/gcb.15798.
⇡11 Pine, M. K., Wilson, L., Jeffs, A. G., McWhinnie, L., Juanes, F., Scuderi, A., & Radford, C. A. (2021). A Gulf in lockdown: How an enforced ban on recreational vessels increased dolphin and fish communication ranges. Global Change Biology, 27(19), 4839–4848. https://doi.org/10.1111/gcb.15798.
⇡12 Gagne, E., Perez-Ortega, B., Hendry, A. P., Melo-Santos, G., Walmsley, S. F., Rege-Colt, M., Austin, M., & May-Collado, L. J. (2022). Dolphin communication during widespread systematic noise reduction-a natural experiment amid COVID-19 lockdowns. Frontiers in Remote Sensing, 3, 934608. https://doi.org/10.3389/frsen.2022.934608.