Uneven seas: seabed litter hotspots, diffuse losses, and the mitigation power of fishing fleets

This study evaluates the efficacy and spatial dynamics of passive Fishing for Litter (FFL) schemes in the Northern Adriatic (Goro) and Southern Tyrrhenian (Salerno) seas. The primary research question is to determine how distinct regional maritime activities and fishing effort influence the quantity, composition, and removal efficiency of seafloor macrolitter. Over a six-month period (2022–2023), 14 commercial bottom trawlers collected litter during routine operations. Despite comparable fleet characteristics, results revealed pronounced spatial heterogeneity; area-standardized removal reached 27.4 kg km−2 in Goro and 92.3 kg km−2 in Salerno, while effort-weighted LPUE differed markedly (2.83 vs 9.57 kg h−1). Stratification of rates showed that hotspot conditions increased LPUE by factors of ∼2.7–3.5, confirming that removal is driven by localized high-density events. Compositional analysis indicated distinct source pathways: diffuse aquaculture debris dominated in Goro, whereas clustered bulky waste (∼73% of mass) characterized Salerno. Annual mitigation potential was estimated at 4.3 t yr−1 (Goro) and 10.2 t yr−1 (Salerno), with modest treatment costs (€1500–€4750 yr−1). These findings demonstrate that FFL is an effective yet spatially dependent tool. Integrating such heterogeneity into assessment frameworks is essential to support MSFD implementation and targeted, ecosystem-based management strategies.