Increases in plastic bottles washing ashore on sub-Antarctic Marion Island

Long-term monitoring of litter stranding on remote islands is an efficient way to track changes in the abundance and composition of floating marine litter. Over 30 years from 1993 to 2024, most beach litter at sub-Antarctic Marion Island derived from offshore sources (95%). The proportion of local, land-based litter decreased from 12% in 1993-1997 to <1% in 2019-2023, mainly due to improved solid waste management at the island's research station. Local litter had a much higher proportion of non-plastic items (68%), especially wood (32%) and metal (22%), than litter items from offshore sources, which were mostly made of plastic (94%). The abundance of fishing gear peaked in the 1990s, when there was a large fishery for Patagonian toothfish (Dissostichus eleginoides) around the island. However, even then, fishing gear comprised only 9% of offshore litter items (7% over the whole study period). Bottles (60%) and pieces of foamed polystyrene packaging (17%) accounted for most offshore litter items. The abundance of offshore litter decreased from 1993 to the early 2000s (change point 2004, 95% CI: 2000-2008), then increased until 2023, mainly due to an increase in the numbers of plastic bottles washing ashore. Our results indicate a worrying increase in general household waste at this remote island in the Southern Ocean.