Do Loggerheads Sea Turtles (Caretta Caretta) Gut Contents Reflect Types, Colours and Sources of Plastic Pollution in the South West Indian Ocean?

Plastic debris ingested by loggerheads from by-catches between 2007 and 2021 in the South West Indian Ocean (SWIO) were analysed. Collected plastic debris accumulated on beaches of the east coasts of Madagascar as a proxy for the ocean plastics, to compare the characteristics of plastics beached with plastic ingested by turtles. A “brand audit” of each plastics (ingested and beached) to determine its country of origin was conducted. An oceanic circulation model was used, to identify the most probable sources of plastics found in the SWIO. The results revealed that 202 of the 266 loggerheads analysed had ingested plastics. Plastics categorized as “hard” and “white” were equally dominant in loggerheads and beaches, suggesting no diet selectivity. Both brand audit and circulation modelling demonstrated that Southeast Asia is the main source of plastic pollution in the region. This study demonstrates that loggerheads are powerful bio-indicators of plastic pollution in the SWI