Reduction of Low-Frequency Vessel Noise in Monterey Bay National Marine Sanctuary During the COVID-19 Pandemic

Abstract

Low-frequency sound from large vessels is a major, global source of ocean noise that can interfere with acoustic communication for a variety of marine animals. Changes in vessel activity provide opportunities to quantify relationships between vessel traffic levels and soundscape conditions in biologically important habitats. Using continuous deep-sea (890 m) recordings acquired ∼20 km (closest point of approach) from offshore shipping lanes, we observed reduction of low-frequency noise within Monterey Bay National Marine Sanctuary (California, United States) associated with changes in vessel traffic during the onset of the COVID-19 pandemic. Acoustic modeling shows that the recording site receives low-frequency vessel noise primarily from the regional shipping lanes rather than via the Sound Fixing and Ranging (SOFAR) channel. Monthly geometric means and percentiles of spectrum levels in the one-third octave band centered at 63 Hz during 2020 were compared with those from the same months of 2018–2019. Spectrum levels were persistently and significantly lower during February through July 2020, although a partial rebound in ambient noise levels was indicated by July. Mean spectrum levels during 2020 were more than 1 dB re 1 μPa2 Hz–1 below those of a previous year during 4 months. The lowest spectrum levels, in June 2020, were as much as 1.9 (mean) and 2.4 (25% exceedance level) dB re 1 μPa2 Hz–1 below levels of previous years. Spectrum levels during 2020 were significantly correlated with large-vessel total gross tonnage derived from economic data, summed across all California ports (r = 0.81, p < 0.05; adjusted r2 = 0.58). They were more highly correlated with regional presence of large vessels, quantified from Automatic Identification System (AIS) vessel tracking data weighted according to vessel speed and modeled acoustic transmission loss (r = 0.92, p < 0.01; adjusted r2 = 0.81). Within the 3-year study period, February–June 2020 exhibited persistently quiet low-frequency noise and anomalously low statewide port activity and regional large-vessel presence. The results illustrate the ephemeral nature of noise pollution by documenting how it responds rapidly to changes in offshore large-vessel traffic, and how this anthropogenic imprint reaches habitat remote from major ports and shipping lanes.

Slower Ship Speed in the Bahamas Due to COVID-19 Produces a Dramatic Reduction in Ocean Sound Levels

“…Globally ships have become the most widespread and predominant anthropogenic source of noise in the ocean (Erbe et al, 2019). Ship source levels are correlated with vessel speed Leaper, 2019;Ryan et al, 2021), but other characteristics such as vessel type, size, draft, and load can all affect noise emissions FIGURE 4 | Speed by ship type, pre-and during COVID-19, with the size of the point scaled to represent the number of ships, error bars representing the standard deviation of the mean speeds and the p-value of the t-test between datasets (*p < 0.05; **p < 0.01) for each ship type. Sample sizes were not large enough for Unspecified and Other ships to be included.…”

Sounding the Call for a Global Library of Underwater Biological Sounds

“…If the observer knows a target species' signal characteristics, these sounds may be more easily detected, but without prior knowledge of either presence or structure of sounds, listening through the noise can be difficult. This has been highlighted by the recent COVID "anthropause" experienced at various aquatic locations around the world (e.g., Bates et al, 2021;De Clippele and Risch, 2021;Dunn et al, 2021;Gabriele et al, 2021;Ryan et al, 2021), where removal of the anthropogenic component of some soundscapes has provided an opportunity to observe sounds (and therefore presence) of marine fauna that might otherwise be lost in the noise (e.g., Pine et al, 2021). However, it is not just anthropogenic noise that limits acoustic detection of marine fauna.…”

Enhanced monitoring of life in the sea is a critical component of conservation management and sustainable economic growth

“…When acoustic data is integrated with other information such as increasing vessel traffic patterns, animal stress hormones, animal physiology, and environmental variables, it is possible to estimate effects of urbanization, human population growth, mining and defense activities, an increase in maritime activity, associated economic expansion [52], and climate variability [50]. Well-coordinated, long-term ocean sound observation systems can produce multi-dimensional time-series datasets with which to characterize soundscapes and the interconnections of overlapping biological, physical, and manmade sound sources [58]. Economic monitoring of the ocean requires a baseline and subsequent acoustic surveys of water column biomass (fish, plankton), benthic biota and habitats, and human-generated sounds at the regional to global scales that complement the Seabed 2030 project, an international initiative to map the bathymetry of the ocean by 2030 [59][60][61].…”