Ingestion and characterization of plastic debris by loggerhead sea turtle, Caretta caretta, in the Balearic Islands.

Plastic waste has become ubiquitous pollutants in seas and oceans and can affect a wide range of species. For some marine species, plastic debris could pose a considerable threat through entanglement, ingestion, and habitat degradation and loss. Sea turtles are one of the most sensitive species, as their migratory behaviour and multifaceted life cycles make these reptiles especially vulnerable to the negative effects of plastic debris. The present study aimed to assess the amount and composition of plastic debris ingested by loggerhead turtles (Caretta caretta, Linnaeus, 1758) in the Balearic Islands Sea, thusly providing new information to complete the knowledge for this topic. In this work, 45 stranded dead C. caretta specimens were necropsied, and their digestive tract content analysed for the presence of plastic debris. Plastic objects were observed in 27 individuals (60.0%), with an average of 12.7 ± 4.7 plastic items per turtle. Litter in the faecal pellet was also monitored in 67 living individuals, observing plastic elements in 46 (68.7%) of the specimens, reporting an average of 9.7 ± 3.3 plastic elements per individual. Overall, 785 plastic items were found, measured, weighed and categorized according to size, colour, shape, and type of polymer. The main elements ingested were plastic sheets that were found in 65.3% of the turtles analysed, being white (42.7%) and transparent (29.2%) the most predominant colours. Most elements were macroplastics (59.3%), while microplastics were not found. Fourier Transform Infrared Spectrometry (FT-IR) analysis showed that high-density polyethylene and polypropylene were the main polymer plastics, representing 42.3% and 33.8% of the total, respectively. In conclusion, the high occurrence of plastic debris determined in the present study evidenced for the first time plastic ingestion in loggerhead turtles in the Balearic Islands, and highlights C. caretta as a bioindicator organism for marine pollution.