Positive effects of the decrease of hydraulic dredging due to the SARS-CoV-2 pandemic on benthic fauna and clam harvesting in the northern Adriatic (Mediterranean Sea)

Abstract

The Northern Adriatic Sea is historically subjected to intensive bottom trawling and hydraulic dredging for clam harvesting, which are known to have deleterious effects on benthic habitats. In order to gather information on the destructive impact of hydraulic dredging, we investigated the abundance and assemblage composition of soft-bottom macrofauna in a coastal area of the North Adriatic Sea (Mediterranean Sea), by comparing the year before and the year after the reduction of the fishing effort imposed by the SARS-CoV-2 pandemic. Our results indicate that macrofaunal assemblages changed significantly in abundance and composition. While bivalves doubled their abundance, other opportunistic scavenger taxa decreased or disappeared. Despite dredging intensity decreased more than 50% in 2020, the harvesting of Chamelea gallina increased from 18,706 tons in 2019 to 19,092 tons in 2020. Overall, it could be concluded that the decrease in clam fishing effort imposed by the lockdown resulted in an increase of the yearly clam harvesting. Our study points out that the recovery of soft-bottom macrofaunal assemblages due to the long-term decrease of clam harvesting has potentially important benefits, and that the establishment of long fishing stops, or of fishery restricted areas / marine protected areas could lead to a more sustainable fishery and the potential increase of the clam fishery yields.