Shoreline litter in French overseas territories

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

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

• map shoreline litter in French overseas territories, focusing on French Overseas Departments and Regions (DROM);
• issue recommendations on the continuation of monitoring in these territories and the monitoring strategy to be implemented.

To this end, during the first year, Cedre inventoried both completed and ongoing monitoring projects and actions relating to marine litter, as well as monitoring data that could support the study. The protocol used in mainland France was revised and adapted to overseas territories, in particular by adding to the macrolitter identification key. Local operators with good knowledge of their local area were identified, contracted, and trained by CEDRE to implement the monitoring protocol at jointly identified shoreline sites. The second year focused on conducting macrolitter surveys at the selected sites, with scientific and technical support from CEDRE to ensure consistency across all studied locations. The data collected was sent to Cedre to be compiled and checked. The third and final year of the project was devoted to analysing and interpreting the results.

For 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" citizen science program led 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 shorelines of French overseas territories in 2024, with median total abundances ranging from 155 items per 100 m in Mayotte to 567 items per 100 m in French Guiana, compared to 386 items per 100 m observed in mainland France the same year. The litter found in French overseas territories is primarily plastic, representing more than 60% in all territories, including items related to food and beverage consumption and a significant share of single-use plastics. The nature and origin of the litter proved, however, to be highly diverse, varying between territories, and often resulting from transboundary inputs.

This study demonstrates the relevance of implementing shoreline litter monitoring in French overseas territories. The methodology tested, which is based on the routine monitoring protocol used in mainland France, proved suitable for overseas environments. It draws on local resources and available tools, sometimes requiring only simple adaptations. The introduction of a permanent, ongoing monitoring programme in these areas would generate data to reinforce the consistency of public policies on marine litter at a national level while addressing the specific challenges of each territory.

Project deliverable:

Feasibility study for the implementation of a shoreline litter monitoring network in French overseas territories (in French)