COVID-19 lockdown reveals fish density may be much higher in marine reserves

Marine reserves generally allow ecotourism to offer an alternative income to fishing. However, we need to assess its impact on wildlife to make this activity sustainable. The COVID-19 lockdown provided a unique opportunity to evaluate wildlife diversity in the absence of human activity. In a Mexican reserve, we monitored fish assemblages before, during, and just after the lockdown. We show that ecotourism activities alter the behavior of fishes by finding a 2.5-fold density rise during the lockdown. We suggest that the noise pollution generated by the numerous recreational vessels is a significant factor of perturbation. In the absence of noise pollution, some fishes may be bolder (less hidden) and others can come back to the reserve from usually quieter areas (e.g., deeper waters). Our results represent a great worldwide incentive to improve the health of marine reserves by establishing concrete measures in managing plans to mitigate noise pollution. Open Research statement All data and code necessary to reproduce the results of the paper are enclosed in the submission for review purposes, and will be published on Zenodo following the acceptance of the paper.