Coastal litter in French Overseas Territories

With the support of around twelve local partners and using the same approach as for coastal litter monitoring in mainland France, Cedre conducted a feasibility study on behalf of the Water and Biodiversity Directorate of the French Ministry of the Environment for the implementation of coastal litter monitoring in French overseas territories.

This 3-year study, initiated in January 2023, aimed to:

• Map coastal litter in French overseas territories, prioritizing French Overseas Departments and Regions (DROM);
• Issue recommendations on the continuation of monitoring in these territories and the surveillance strategy to be implemented.

To this end, during the first year, Cedre catalogued past and ongoing monitoring projects and actions related to marine litter, as well as monitoring data likely to support the study. The protocol used in mainland France was reviewed and adapted to overseas territories, specifically enriching the identification grid for macrolitter. Local operators with good knowledge of their territories were identified, contracted, and trained by Cedre to implement the monitoring protocol at jointly identified coastal sites. The second year focused on conducting macrolitter surveys at selected sites, with scientific and technical support from Cedre to ensure consistency across all studied locations. Once collected, data were transmitted to Cedre for centralization and quality control. The third and final year of the project was dedicated to analyzing and interpreting the results.

As part of this study, 87 surveys were conducted in 2024 at 24 sites across the various overseas territories: Guadeloupe (two sites), Martinique (four sites), French Guiana (two sites), Reunion Island (two sites), Mayotte (eight sites), and the Scattered Islands in the French Southern and Antarctic Lands (six sites). Data from the "Plastique à la loupe" participatory science program by the Tara Ocean Foundation, as well as opportunistic monitoring in New Caledonia, French Polynesia, and Saint Pierre and Miquelon, were also integrated to enrich the study.

The results show that litter was found in abundance on the coastlines of overseas territories in 2024, with median total abundances ranging from 155 items/100m in Mayotte to 567 items/100m in French Guiana, compared to 386 items/100m observed in mainland France the same year. Litter found overseas is primarily plastic, representing more than 60% across all territories, including items related to food and beverage consumption and a significant share of single-use plastics. However, the nature and origin of the litter proved to be highly diverse and variable between territories, often resulting from transboundary inputs.

This study demonstrates the relevance of implementing coastal litter monitoring in French overseas territories. The methodology tested, which is based on the regular monitoring protocol used in mainland France, proved suitable for overseas environments. It relies on local resources and available tools, sometimes requiring only simple optimizations. Sustaining this monitoring would generate surveillance data that strengthens the consistency of public policies against marine litter at a national scale while addressing the specific challenges of each territory.

Project Deliverable:

Feasibility study for the implementation of a coastal litter monitoring network in French Overseas Territories