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Cory's shearwater as a key bioindicator for monitoring floating plastics
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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.
The potential of using organisms as bioindicators of marine litter has been an area of general interest in multiple scientific and monitoring programs across the globe. Procellariiformes seabirds are particularly vulnerable to plastic contamination, which makes them a research focus group. This study investigated plastic ingestion in deceased fledglings and adults Cory's shearwaters (Calonectris borealis) collected over eight years (2015 to 2022) at two Atlantic archipelagos: the Azores and the Canaries. Necropsies were carried out in a total of 1,238 individuals showing a high prevalence of plastic ingestion (90%), with approximately 80% of items recovered from the gizzard. Fledglings carried greater plastic loads compared to adults, yet plastic morphologies were similar between both age classes. The temporal analyses conducted with generalised additive mixed-effect models revealed a distinct temporal trend in plastic numbers, but not in terms of plastic mass. In addition, the spatial analyses showed that Cory's shearwaters from the Canary Islands ingest a higher quantity of plastic and a greater proportion of threadlike items than the Azorean birds. These results suggest higher contamination at the NW Africa foraging grounds next to the Canaries and highlight fisheries as a potential source of marine litter in that region. On the other hand, the information gathered from the Azorean birds suggests they would be able to monitor changes in the composition of the plastic items floating in the North Atlantic Subtropical Gyre. Overall, our outcomes support the use of Cory's shearwater fledglings that are victims of light pollution as a key bioindicator of plastic contamination in the North Atlantic. For its policy application, the presented threshold value in combination with the assessment method will enable effective tracking of floating plastic litter in the framework of the MSFD and OSPAR.
More Papers Like This
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.
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.
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.
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.
Barau's petrel, Pterodroma baraui, as a bioindicator of plastic pollution in the South-West Indian Ocean: A multifaceted approach
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This study evaluated Barau's petrel as a bioindicator of plastic pollution in the South-West Indian Ocean using necropsies, GPS tracking, manta trawling, and dispersal modeling, finding that 71% of analyzed birds had ingested plastic. GPS tracking showed adults consistently foraged in high-plastic-concentration areas, with the highest ingestion risk in the northwest of Reunion Island and at latitude 30°S, confirming the species as a reliable regional bioindicator.
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