Underwater Acoustic Impacts of COVID-19

Updated October 16, 2020

Introduction

The novel coronavirus (COVID-19) has had a major impact on society around the globe. Shelter-in-place orders and non-essential travel bans have had significant effects at all levels, from local to national economies. There have been unexpected, wide-ranging, trickle-down effects from these changes, including shifts in local and regional underwater noise budgets. Unprecedented slowdowns in industrial, transportation, and recreational activities have led to less anthropogenic noise from sources such as construction, buses, cars, ships, and aircraft. The decrease in human activities have even 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), 176–177. https://doi.org/10.1038/d41586-020-00965-x.. This has been measured by existing land-based seismometers that allow geologists to spot and monitor earthquakes and other seismic events.

Hydrophone Recordings: Canada

Changes in ambient noise correlated with COVID-19 have also been detected underwater. As part of health and safety measures related to the pandemic, commercial, research, and other types of vessel traffic have been reduced or completely halted. With a global reduction in vessel traffic, there has been a corresponding reduction in the underwater noise caused by human activities. Barclay and Thomson (2020)[2] 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. reviewed underwater acoustics data recorded by four, bottom-mounted, hydrophone stations, which are part of of Ocean Network Canada’s (ONC) VENUS and NEPTUNE underwater observatories. The hydrophone stations have been recording since at least October of 2018 and have at least a year of pre-pandemic baseline data for comparison. One station is on the Endeavor node of the NEPTUNE observatory, a deeper water hydrophone station located near the Juan de Fuca Ridge (#1 in figure below). The second station is on the Pacific continental slope, associated with the Clayoquot Slope node of the NEPTUNE observatory (#2 in figure below). Two stations, associated with the Central and East nodes of the VENUS observatory (#3 and #4 in figure below), are located in the Strait of Georgia, between Vancouver Island and the British Columbia mainland. The scientists’ analysis of the hydrophone data focused on low frequency signals (100 Hz) to isolate underwater sound produced by shipping. Automatic identification system (AIS) data and shipping and trade statistics were also used to assess shipping activity.

Bathymetric map displaying the British Columbia mainland, Vancouver Island, and the locations of the four Ocean Networks Canada ocean observatory hydrophone stations: Central and East nodes of the VENUS observatory (3, 4) Clayoquot Slope node of the NEPTUNE observatory (2), and the Endeavor node of the NEPTUNE observatory (1). Reproduced from – Thomson, D.J.M. and D.R. Barclay. (2020)[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. , with the permission of the Acoustical Society of America

In response to the COVID-19 pandemic in Canada, all commercial marine vessels with the capacity of 12 or more passengers ceased non-essential activities in March 2020. Until October 31, 2020, cruise ships cannot navigate, transit, or moor in Canadian Arctic waters. 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 reduction during the first three months of 2020, which they 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. [4] 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)[5] 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. , with the permission of the Acoustical Society of America.

ONC hydrophones have shown underwater sound in the shipping frequency band to slowly increase in June and July 2020 (figure below). Relative underwater sound levels (at 100 Hz) are 1-5 dB less than pre-COVID levels 99% of the time at the Central Strait of Georgia ONC platform (shown in the bottom panel), but 1% of time (top panel), noise intensities are as much as 5 dB greater than pre-COVID levels. Although ferry activities remain reduced, and there are no cruise ships in the area, commercial shipping activity is returning to pre-COVID levels. Scientists correlate the rise in low frequency noise with this increase in commercial shipping activity in the area.

Relative noise level recorded at the Central Strait of Georgia Ocean Networks Canada platform at 100 Hz. The blue and red lines indicate different hydrophone deployments. Each panel presents a percentile of the data calculated where the 1st percentile means 1% of the noise is louder and the 99th percentile means 99% of the noise is louder. Image/data credit: Ocean Networks Canada.

Southern Resident Killer Whales

Scientists are investigating what potential effect the reduction in vessel traffic noise might have on local marine life, including various cetacean species at risk, such as the critically endangered population of southern resident killer whales (SRKW). Underwater sound associated with commercial vessel traffic is a recognized threat to the SRKW population’s survival. In the summer months, these whales concentrate in the coastal waters off the southern end of Vancouver Island in Canada and northern Washington State in the U.S. Researchers are monitoring the SRKW population for potential behavioral changes related to underwater acoustic shifts associated with COVID-19. However, they will not know how changes in anthropogenic noise may have impacted the whales on a population level for some time. Barclay and Thomson will continue to review the VENUS and NEPTUNE ocean observatory hydrophone data in detail over the entirety of the pandemic.

In July 2020 an oceannetworks canada hydrophone in the Strait of Georgia captured the sound of southern resident killer whales communicating both in hushed seas (due to the COVID-19 slowdown) and while a vessel passes nearby.Video used with permission from Ocean Networks Canada.

 

Hydrophone Recordings: Other Locations

Scientists recover an acoustic mooring from NOAA’s Cordell Bank National Marine Sanctuary. Image credit: NOAA/NMS.

Scientists will also analyze data from acoustic recording instruments at other underwater locations, providing further data on the potential underwater acoustic effects of COVID-19. Researchers hope to analyze acoustic changes in the marine environment of the Cordell Bank National Marine Sanctuary (CBNMS), located offshore of San Francisco, California, USA. In 2015, the National Oceanic and Atmospheric Administration (NOAA) established a long-term, continuous, low-frequency (10 Hz–2 kHz) passive acoustic monitoring site in the sanctuary.  Recent analyses showed vessel traffic and underwater whale sounds to substantially contribute to the sanctuary’s low-frequency (< 100 Hz) ambient sound environment, with vessel sounds present year-round and whale vocalizations showing seasonal peaks [6]Haver, S. M., Rand, Z., Hatch, L. T., Lipski, D., Dziak, R. P., Gedamke, J., Haxel, J., Heppell, S. A., Jahncke, J., McKenna, M. F., Mellinger, D. K., Oestreich, W. K., Roche, L., Ryan, J., & Van Parijs, S. M. (2020). Seasonal trends and primary contributors to the low-frequency soundscape of the Cordell Bank National Marine Sanctuary. The Journal of the Acoustical Society of America, 148(2), 845–858. https://doi.org/10.1121/10.0001726.. Characterization of low-frequency ambient sound levels in the CBNMS will help to establish an initial baseline for understanding the site’s underwater acoustic environment; scientists aim to analyze acoustic changes in the CBNMS as the COVID-19 pandemic set in and ship traffic was reduced in the region.

This is not the first time underwater sound associated with vessel traffic has reduced suddenly. Following the September 11th terrorist attacks in New York City, all non-essential vessel traffic was halted along many North American shipping routes. This temporary pause in shipping provided a unique and unplanned opportunity for scientists studying North Atlantic right whales in the Bay of Fundy, Canada. They noted a 6 dB decrease in underwater noise with a significant reduction below 150 Hz. It was concluded that these acoustic changes were a consequence of reduced large vessel traffic in the Bay of Fundy[7]Rolland, R. M., Parks, S. E., Hunt, K. E., Castellote, M., Corkeron, P. J., Nowacek, D. P., Wasser, S. K., & Kraus, S. D. (2012). Evidence that ship noise increases stress in right whales. Proceedings of the Royal Society B: Biological Sciences, 279(1737), 2363–2368. https://doi.org/10.1098/rspb.2011.2429..

Barclay and Thomson will continue to review the VENUS and NEPTUNE ocean observatory hydrophone data in detail over the entirety of the pandemic. Once at-sea oceanographic research resumes, other scientists will work to retrieve additional instruments, and further data on the potential underwater acoustic effects of COVID-19 will be compiled.

COVID, Underwater Sound, and Recreational Boating

It is also important to note that not all marine environments have experienced underwater sound reductions associated with COVID-19. In contrast to decreases in commercial shipping and other large vessel activities, recreational boating has increased over the course of the pandemic. As society shifted its focus to outside activities, a substantial increase in boater traffic has been noted in coastal areas such as Sarasota, Florida, U.S.A. Underwater sounds associated with recreational boats and other personal watercraft may disrupt communication between resident bottlenose dolphins in these waters. Scientists found that the dolphins compensate for increased underwater noise by adjusting the amplitude of their whistles (Lombard response) [8]Kragh, I. M., McHugh, K., Wells, R. S., Sayigh, L. S., Janik, V. M., Tyack, P. L., & Jensen, F. H. (2019). Signal-specific amplitude adjustment to noise in common bottlenose dolphins ( Tursiops truncatus ). The Journal of Experimental Biology, 222(23), jeb216606. https://doi.org/10.1242/jeb.216606.. Using acoustic recording tags, scientists measured dolphin whistle characteristics in the presence of small boats. When a recreational boat passed, the dolphins raised the intensity of their whistles by 0.1– 0.3 dB for every 1 dB rise in the background noise. This is a reduced response, whereas larger whales (e.g., killer whales and North Atlantic right whales) have been shown to match the increase in the intensity of their calls to the increase in the background noise level.

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Cited References

1 Gibney, E. (2020). Coronavirus lockdowns have changed the way Earth moves. Nature, 580(7802), 176–177. https://doi.org/10.1038/d41586-020-00965-x.
2, 3, 4, 5 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.
6 Haver, S. M., Rand, Z., Hatch, L. T., Lipski, D., Dziak, R. P., Gedamke, J., Haxel, J., Heppell, S. A., Jahncke, J., McKenna, M. F., Mellinger, D. K., Oestreich, W. K., Roche, L., Ryan, J., & Van Parijs, S. M. (2020). Seasonal trends and primary contributors to the low-frequency soundscape of the Cordell Bank National Marine Sanctuary. The Journal of the Acoustical Society of America, 148(2), 845–858. https://doi.org/10.1121/10.0001726.
7 Rolland, R. M., Parks, S. E., Hunt, K. E., Castellote, M., Corkeron, P. J., Nowacek, D. P., Wasser, S. K., & Kraus, S. D. (2012). Evidence that ship noise increases stress in right whales. Proceedings of the Royal Society B: Biological Sciences, 279(1737), 2363–2368. https://doi.org/10.1098/rspb.2011.2429.
8 Kragh, I. M., McHugh, K., Wells, R. S., Sayigh, L. S., Janik, V. M., Tyack, P. L., & Jensen, F. H. (2019). Signal-specific amplitude adjustment to noise in common bottlenose dolphins ( Tursiops truncatus ). The Journal of Experimental Biology, 222(23), jeb216606. https://doi.org/10.1242/jeb.216606.