Changes in cetacean presence and behavior in response to reduced marine traffic - the effects of a nationwide lockdown

Abstract: Creating noise-pollution and other disturbances, marine traffic poses a great threat to marine mammals all over the world which may demonstrate through short- and long-term changes in behavior and distribution. The Covid-19 lockdown in 2020 provided a setting to study the effects of marine traffic on cetacean presence and interactive behavior. We investigated the effects of fluctuations in both general marine traffic and whale-watching vessels that resulted from lockdown. Observational data in the North Atlantic Ocean off the coast of southern Tenerife was used, which have been collected during whale-watching tours between 2017-2021. The analysis showed that the decrease in general marine traffic in 2020 was mirrored in a lower number of whale-watching vessels present during cetacean observations. This reduction in boat traffic had a significant effect on how often the animals would approach the boat or stay indifferent to the presence of the boat among the resident species, with a significant increase in boat approaches and a significant decrease in indifference to boats after lockdown. We did not find a difference in presence for either resident or non-resident species as a group after lockdown, however, there was a significant increase of one individual species - the Atlantic spotted dolphin - after lockdown. Even though the resident species are living in a protected area, our results suggest that they are still affected by a high frequency of boats and boat interactions. To enhance the wellbeing of both resident and visiting populations, further management should be implemented, such as spatial or temporal boat-free zones as well as improvements on how whale-watching is performed.