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

Abstract

As underwater noise from ship traffic increases, profound effects on the marine environment highlight the need for improved mitigation measures. One measure, reduction in ship speed, has been shown to be one of the key drivers in reducing sound source levels of vessels. In 2017, a study began to assess the impacts of increasing commercial shipping traffic on sperm whales in Northwest Providence Channel, northern Bahamas, an international trade route that primarily serves the southeast US. Ship data were collected from an Automatic Identification System (AIS) station combined with recordings from an acoustic recorder to measure underwater sound levels and to detect the presence of sperm whales. Here we analyze a subset of these data to opportunistically investigate potential changes in ship traffic before and during the COVID-19 pandemic. These data span one calendar year from October 2019 to October 2020. A pre-COVID-19 dataset of 121 days, from a recorder approximately 2 km from the shipping route was compared to a 134-day dataset collected during COVID-19 from the same site, comprising 2900 and 3181 ten-minute recordings, respectively. A dramatic decrease in ocean noise levels concurrent with changes in shipping activity occurred during the pandemic. The mean pre-COVID-19 power density level in the 111–140 Hz 1/3-octave band was 88.81 dB re 1 μPa (range 81.38–100.90) and decreased to 84.27 dB re 1 μPa (range 78.60–99.51) during COVID-19, equating to a 41% reduction in sound pressure levels (SPL). After differences in seasonal changes in wind speed were accounted for, SPL decreased during the pandemic by 3.98 dB (37%). The most notable changes in ship activity were significantly reduced vessel speeds for all ship types and fewer ships using the area during the pandemic. Vessel speed was highly correlated to SPL and the only ship-based variable that predicted SPLs. Despite the opportunistic nature [i.e., not a standard before-after-control-impact (BACI) study], this study provides a unique opportunity to assess the effectiveness of ship traffic management strategies, such as slowing ships down, to mitigate impacts on marine life in the study area, including local sperm whale populations.

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.…”

Anthropause shows differential influence of tourism and a no‐take reserve on the abundance and size of two fished species

“…Abundance increases in older fishes have preceded recruitment increases while harvest was paused in other systems (Beare et al, 2010); thus, there is precedent for a rapid increase in spawning stock following closure. Deleterious shipping noise decreased in The Bahamas during the closures (Dunn et al, 2021), removing a potential stressor for wide-ranging but reef-associated fish like grouper (Duarte et al, 2021). It is plausible that the anthropause decreased both harvest and indirect stressors such that divers saw more grouper, especially in the well-protected and isolated habitats within the MPA.…”

Impact of the COVID-19 pandemic on levels of deep-ocean acoustic noise

“…Recent studies looking at the North Sea showed a decline in sound pressure of 13% (reduction in sound pressure level of 1.2 dB) for frequencies in the range 10 Hz to 1 kHz corresponding to reduced level of shipping activity 24 . Some studies focused on local changes in soundscape have ascribed the reductions in sound levels to a pandemic-induced reduction in vessel speed rather than vessel numbers 25 , and significant local reductions have been observed where transport links such as ferries shut down during the pandemic 26 .…”

“…than vessel numbers 25 , and significant local reductions have been observed where transport links such as ferries shut down during the pandemic 26 .…”