From shipping routes to shorelines: assessing vessel-derived marine litter in Fuerteventura, Canary Islands.

Accurate source apportionment of marine litter is critical for effective mitigation, yet standard typology-based methods may misrepresent source contributions, particularly on oceanic islands. This study investigates the composition and probable origins of marine litter on Fuerteventura (Canary Islands) using a comprehensive inventory of 494,903 coastal and 687 offshore macro-litter items collected over three years between 2021 and 2023. Plastics dominated both coastal and offshore debris, accounting for more than 70% of items in each compartment, while abandoned, lost, or otherwise discarded fishing gear (ALDFG) represented a substantial proportion of the litter pool. Conventional probabilistic source attribution using the Tudor & Williams framework primarily assigned coastal debris to land-based sources, particularly beach tourism, whereas fishing and shipping received lower contributions. However, independent indicators suggested a greater maritime contribution than indicated by typology-based attribution alone. Foreign-labelled PET bottles were predominantly unweathered, while debris accumulated on remote beaches with limited terrestrial inputs. Lagrangian simulations demonstrated connectivity between surveyed coastlines and eastern Atlantic shipping corridors, with particles reaching these routes within 10-15 days. Commercial containers were observed as improvised fishing buoys, illustrating how classification according to original product type can obscure their actual maritime function. These findings indicate that typology-based source-apportionment approaches may underestimate maritime contributions to coastal litter in oceanic island settings. OSPAR protocols should incorporate parameters such as degradation state, product provenance, and observed functional use to improve source discrimination. The results also highlight the need for enhanced monitoring and enforcement of marine waste regulations along high-traffic shipping and fishing corridors.