Characterization of Plastics Ingested by the Bioindicator Cory’s Shearwater from Tenerife Island (Canary Islands): Implications for Marine Environmental Monitoring

Plastic pollution is a pressing environmental concern globally, especially in marine ecosystems. In this study, the evaluation of the potential ingestion of plastic, mostly in the form of microplastics (MPs), by fledglings of Cory’s shearwaters (Calonectris borealis) from the Canary Islands (Spain) was conducted. The total number of plastics found in the stomach samples was 674, primarily comprising large MPs (1–5 mm: 82%), followed by mesoplastics (>5–25 mm: 18%). The predominant morphology was threadlike (31.6%), followed by hard, irregularly shaped fragments (28.3%), microspheres (22.4%), and sheets (15.7%). Loads were found to overlap with those described for the same species in highly populated areas such as the Mediterranean Sea. Plastic counts above Cory’s threshold value may suggest poor environmental status for the Canary Current region. FTIR-ATR analysis evidenced the predominance of polyethylene (PE) (46.7%), polypropylene (PP) (24.6%) and polyamide (PA) (20.4%). This is likely linked not only to the fact that PE is the most produced plastic worldwide, but also the fact that, along with PP, it makes up the highest amount of single-use plastic products. Overall, findings provide a contamination-controlled, FTIR-verified baseline for fledglings from Tenerife; however, given the limited, single-season sample (n = 33) and opportunistic design, results are descriptive and not intended for population-level inference. Yet, the potential of Cory’s shearwater as a sentinel species to monitor plastic pollution is highlighted, emphasizing the urgent need for effective mitigation strategies to address plastic pollution in marine environments.