Quantifying and Analyzing Plastic in Seabird Nests in the North Sea
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Abstract
Plastics in the environment are of increasing concern for many organisms including seabirds. In this study, I examined the nests of four seabird species – northern gannets, black-legged kittiwakes, great cormorants, and gulls (herring and lesser black-backed gulls) – on two small islands in the North Sea. I quantified the proportion of plastic in each nest following methods described by Thompson et al. (2020), and compared the types and colors of plastics in their nests to those found in the environment. I examined the proportion of nests of each species that contained plastic, and found that northern gannets (98%) and great cormorants (95%) were both more likely to include plastic in their nests than kittiwakes (44%) and gulls (28%). I also found that the average amount of plastic in nests differed across species (northern gannets 36%, great cormorants 9%, black-legged kittiwakes 2%, gulls 1%). These differences in proportions of nests containing plastic and average amount of plastic in nests are likely due to differences in materials used in nests and whether a species reuses nests each year. In comparing plastics in the environment to that in nests, I found that fibrous plastic, in particular dolly rope, a type of sacrificial chafing material used in commercial bottom trawling fishing, was highly preferred by all the studied seabird species. Orange dolly rope was also favored over other colors of dolly rope. Chemical testing of dolly rope pieces found that it was polyethylene, which is consistent with previous reports for the North Sea, and mechanical testing of dolly rope strands highlighted the dangers of entanglement posed by the material. There is a strong preference for orange dolly rope by nesting birds that may be due to morphological similarities to natural nesting material and an ease in locating the brightly colored material in the water. While seabird deaths by entanglement alone are not likely to lead to a population decrease, these deaths are often slow and painful and should be prevented if only for humanitarian reasons. I explore different methods of mitigating deaths by entanglement and reducing plastics in the marine environment, as well as ways in which plastic monitoring in seabird nests can provide information regarding the levels and types of pollution in the marine environment.
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Plastic, Seabird, North Sea, Commercial fishing, Environmental plastic, Plastic pollution