Association of ocean macroplastic debris with stranded sea turtles in the Central Gulf of Thailand

The impact of macroplastic debris (> 5 mm) on marine life is a global concern but has rarely been investigated in Thailand. This study investigated the relationship between stranded sea turtles and macroplastics in the Central Gulf of Thailand. Records of stranded turtles (n = 388) from 2017-2020 were analysed retrospectively to determine their interaction with macroplastics. In addition, macroplastics collected from the gastrointestinal (GI) tracts of 30 dead stranded turtles and 13 beaches (along a 100 m transect mid-way between high and low tide) between 2019 and 2020 were investigated. Types and composition of macroplastics were identified with the use of a stereomicroscope and Fourier-transform infrared spectrometer. Green turtles Chelonia mydas comprised the majority of stranded turtles (74%, n = 251), and macroplastics (entanglement or ingestion) were the leading cause of death (n = 152). Most stranded turtles were juveniles (65%), and their stranding was significantly correlated with macroplastics (p < 0.001). Juveniles were more prone than adults to become entangled (p = 0.007), while adults had a higher ingestion rate than juveniles (p = 0.009). Plastic fibres were commonly found in the GI tracts (62%, n = 152 of 244) and beaches (64%, n = 74 of 115). Most fibres from the GI tracts (83%, n = 126 of 152) and beaches (93%, n = 68 of 74) were fishing nets made of polyethylene or polypropylene. We conclude that fishing nets are a significant cause of sea turtle stranding in the Central Gulf of Thailand, and this issue requires immediate resolution.