Tracking the global reduction of marine traffic during the COVID-19 pandemic

The COVID-19 pandemic, characterized by widespread mobility restrictions, created an "anthropause"—a period of reduced human activity. This event significantly impacted transportation, energy consumption, and consumer demand, leading to changes in human stressors on the natural environment. Quantifying the magnitude and patterns of these changes at sea is crucial for understanding the impacts on the blue economy and the marine environment. Human activities at sea were profoundly affected, with port restrictions and altered consumption patterns impacting fisheries, passenger ferries, and cruise ships. Changes in vessel movement, similar to previous economic recessions, likely resulted in short- and long-term effects on various anthropogenic pressures, including air pollution, invasive species spread, and collisions with marine animals. Localized studies have reported short-term declines in underwater noise, water turbidity, and fishing effort due to reduced vessel activity. However, the spatio-temporal effects of COVID-19 on ship-based activities remain unclear at global and regional scales. Recent advancements in Automatic Identification System (AIS) technology, particularly satellite-based AIS (S-AIS), enable global monitoring of ship mobility patterns at high spatio-temporal resolution. AIS transmits real-time vessel information via VHF radio transponders, mandatory for large vessels and increasingly used voluntarily by smaller ones. While limitations exist (e.g., small vessels lacking AIS, transmission gaps), AIS data offer unparalleled insights into shipping impacts and conservation planning. This study uses AIS data to comprehensively assess short-term changes in ship-based mobility patterns in response to COVID-19 across multiple sectors and spatio-temporal scales. A global assessment using monthly traffic density maps evaluates changes relative to 2019. A high-resolution (daily) assessment in the Western Mediterranean Sea, a key region for global shipping and cruise tourism, provides further insights.

Previous research has highlighted the impacts of reduced human activity on various aspects of the environment during periods of reduced mobility, such as the anthropause caused by COVID-19 lockdowns. Studies have documented the effects on biodiversity conservation, CO2 emissions, and air quality. The impact of the 2008 financial crisis on shipping and its subsequent effects on benthic ecosystems and air quality has also been investigated. Prior work has utilized AIS data for assessing shipping-derived impacts, conservation planning, and the potential spread of diseases like COVID-19. However, a comprehensive global and regional assessment of the impact of COVID-19 lockdowns on marine traffic across multiple maritime sectors was lacking before this study.

This study employed two main datasets: satellite AIS (S-AIS) data from exactEarth Ltd. for global analyses and terrestrial AIS (T-AIS) data from the Balearic Islands Coastal Observing and Forecasting System (SOCIB) for the Western Mediterranean Sea. For the global assessment, monthly density maps (0.25-degree resolution) from S-AIS were used to compare traffic density in the first half of 2020 with the same period in 2019. Vessels were categorized into cargo, tanker, passenger, fishing, and "other." Changes in traffic density and occupancy were calculated. The Oxford COVID-19 Government Response Tracker (OxCGRT) Stringency Index was used to compare government measures across countries. Linear mixed models (LMMs) assessed the effects of confinement measures on marine traffic density at the country level. For the regional assessment in the Western Mediterranean, daily counts of vessels underway were obtained from T-AIS data (January 1, 2016 – November 30, 2020). Vessels were categorized similarly to the global analysis, with the addition of a "recreational" category. The number of vessels underway each day in 2020 was compared to equivalent periods in 2019 to quantify the impact of the pandemic. The analysis included an examination of changes in traffic around 10 selected maritime chokepoints to identify areas where changes might otherwise be masked. The study also analyzed changes in traffic density within the Exclusive Economic Zones (EEZs) of various countries, considering their income levels as categorized by the World Bank. Data processing and quality control procedures are detailed in the supplementary methods section.

The global assessment revealed a decline in marine traffic during the COVID-19 pandemic, impacting multiple sectors. Decreases were observed in 70.2% of the analyzed EEZs. The most significant reduction in traffic density peaked in April 2020, with a 1.4% decrease in occupancy across all vessel types. Passenger vessels showed the most substantial and prolonged decline. Regional variations were apparent. European seas experienced the most significant reductions, while East Asia exhibited a more mixed pattern, with increases in traffic within China's EEZ potentially reflecting an earlier easing of lockdown measures. Analysis of 10 maritime chokepoints showed varied responses across sectors and locations. The Panama Canal, Strait of Gibraltar, Strait of Dover, and Bosphorus Strait experienced marked decreases in traffic, primarily due to reduced cargo and "other" vessel activity, while the Cape of Good Hope saw increases driven by cargo traffic. The regional analysis in the Western Mediterranean showed a significant reduction in marine traffic after the WHO pandemic declaration, affecting all vessel categories. The most significant declines were observed in passenger and recreational vessels, which experienced slower recovery rates compared to cargo, tanker, and fishing vessels. Linear mixed models indicated a significant effect of the Stringency Index on the change in marine traffic density for all vessel categories except fishing vessels, suggesting that government restrictions had a considerable impact on vessel activity across most sectors. Lower-income countries were less affected by these measures. The overall increase in traffic occupancy prior to the pandemic suggests that comparing 2020 data with 2019 likely underestimates the pandemic's impact. The study also noted several potential non-COVID-19 related factors influencing observed changes, including oil price fluctuations, route changes to avoid Suez Canal tolls, annual shifts in fishing grounds, and national regulations mandating AIS usage.

This study provides a comprehensive overview of the impact of COVID-19 lockdowns on global and regional marine traffic. The findings reveal an unprecedented reduction across multiple sectors, with passenger and recreational vessels experiencing the most substantial and prolonged declines. The relatively lower impact on the maritime transport sector highlights the global interconnectedness and reliance on international goods. The uneven impact on fisheries suggests vulnerability varies among fishing fleets. The rapid recovery of the fishing sector in the Western Mediterranean, particularly industrial fisheries, suggests resilience due to resources and subsidies. However, the study acknowledges the need for further investigation into the impacts on small-scale fisheries in low-income countries. The observed changes highlight the considerable influence of policy actions related to COVID-19 restrictions and economic factors on vessel activity. The study's spatial and temporal heterogeneity of changes is important for assessing environmental consequences. The reduction in marine traffic in certain areas might offer some positive environmental outcomes (e.g., reduced noise pollution, improved water quality), but potential negative impacts (e.g., increased illegal fishing) also need consideration. The findings align with other studies reporting reductions in underwater sound and water turbidity. Future research should investigate the long-term effects of COVID-19 on the blue economy and marine ecosystems, considering multiple factors influencing vessel activity.

This study presents the first near real-time global-scale quantification and mapping of the impact of COVID-19 on marine traffic, leveraging advanced AIS technology. The findings highlight significant reductions across various sectors, with regional variations reflecting differences in lockdown measures and economic conditions. The results underscore the need for continued monitoring of long-term impacts and the importance of incorporating diverse factors for a more nuanced understanding of the interaction between human activities and the marine environment. Future research could focus on detailed regional and sectoral studies, exploring longer-term impacts on ecosystems and the blue economy. Implementing autonomous real-time monitoring systems will improve ocean observation, contributing to more effective conservation strategies.

The study acknowledges some limitations inherent to AIS data. These include the possibility of incomplete coverage for smaller vessels, transmission gaps, and potential inaccuracies in vessel type classification. The analysis assumes that changes observed in 2020 were primarily driven by the COVID-19 pandemic, while acknowledging that other factors might have also influenced vessel activity. Future studies should investigate the relative contributions of different factors to observed changes. The regional study focused on the Western Mediterranean might not be fully generalizable to other regions with different geographic and socio-economic conditions. The study also highlights the need for continued data collection and analysis to better understand long-term trends and impacts.