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Plastic ingestion by Cory's and Scopoli's shearwaters (Calonectris spp.) from the north-eastern Atlantic Ocean and Mediterranean Sea
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This study documented plastic ingestion in 529 individuals of two Calonectris shearwater species (C. borealis and C. diomedea) from the northeast Atlantic and Mediterranean, finding higher plastic loads in Mediterranean birds and fledglings compared to post-fledglings. The authors proposed a mass-based threshold monitoring system, suggesting thresholds of 0.0098 g for fledglings and 0.0041 g for post-fledglings, under which 40–88% of birds depending on location exceeded the threshold, advocating this approach over particle-count methods.
Plastic ingestion by seabirds reflects plastic levels in their marine environment and therefore seabirds are monitored within the EU Marine Strategy Framework Directive to track the distribution and trends of plastic pollution. We present plastic ingestion data from 529 individuals of two Calonectris species (C. borealis and C. diomedea) from corpses collected across the north-eastern Atlantic Ocean and the Mediterranean Sea. Overall, birds from the Mediterranean ingested more plastics than those from the Atlantic, and fledglings carried higher plastic loads than post-fledglings. In contrast to an earlier proposal to monitor and define plastic ingestion thresholds by the number of particles, we advocate a mass-based system. Plastic mass better reflects environmental contamination and biological harm than particle counts, which can be inflated by fragmentation and are less ecologically relevant than the actual volume ingested. Using the cleanest 10 % of individuals in the most polluted population as a reference, we suggest Threshold values of 0.0098 g for fledglings and 0.0041 g for post-fledglings. According to this definition, between 40 and 88 % of birds exceeded the Threshold, depending on the sampling location. This mass-based Threshold offers an ecologically meaningful metric, and we recommend this approach for plastic pollution monitoring in the northeast Atlantic and the Mediterranean.
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A study of 1,238 Cory's shearwaters necropsied over eight years at the Azores and Canary Islands found 90% plastic ingestion prevalence, with fledglings carrying greater plastic loads than adults and Canary Islands birds ingesting more plastic than Azorean birds. The study proposes a threshold value (less than 33% of turtles with more than 0.05 g ingested plastic) as a bioindicator benchmark for monitoring North Atlantic plastic pollution under the EU Marine Strategy Framework Directive.
Plastic ingestion in Scopoli's shearwater (Calonectris diomedea) from Lampedusa (Italy), central Mediterranean Sea
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Scientists studying seabirds in the Mediterranean found that nearly every bird they examined had swallowed plastic, with young female birds carrying surprisingly high amounts. This matters because these seabirds eat the same fish that end up on our dinner plates, meaning the plastic pollution choking marine life is part of the same ocean food web humans rely on for seafood.
Seabird biomonitoring indicates similar plastic pollution throughout the Canary Current
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Over 90% of Cory's shearwater fledglings sampled across three Canary Islands contained plastic, with white and transparent threadlike fragments predominating, likely from regional fishing activities. Despite spatial segregation in adult foraging areas across the Canary Current, no significant differences in plastic ingestion were detected between colonies, establishing shearwaters as effective regional plastic pollution bioindicators.
Characterization of Plastics Ingested by the Bioindicator Cory’s Shearwater from Tenerife Island (Canary Islands): Implications for Marine Environmental Monitoring
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Researchers characterised 674 plastic items found in the stomachs of Cory's shearwater fledglings from the Canary Islands, finding that ingested plastics were predominantly large microplastics (1-5 mm, 82%) with threadlike morphology, and that the birds serve as effective bioindicators of marine plastic pollution in the eastern Atlantic.
Plastics reset in an adult Procellariform seabird species during the breeding season
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This study tracked temporal dynamics of ingested plastics in 96 adult Cory's shearwaters across three nesting periods over seven years in the Azores, finding that plastic loads decreased markedly during the breeding season, with over 80% of stomach plastic apparently transferred to offspring during chick-rearing. The results suggest that fledglings rather than breeding adults are better indicators of plastic contamination, and that adult plastic loads at breeding sites may reflect conditions from distant wintering migration routes.
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