Characterizing Plastic Ingestion By Bonin Petrels (Pterodroma hypoleuca) From Midway Atoll: Towards Plastic Pollution Bio-Indicators for the Northwestern Hawaiian Islands
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Chamberlain, Lauren
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Marine Science
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Abstract
Tubenose seabirds (order Procellariformes) are effective biological indicators of marine plastic debris due to their surface-foraging behaviors, broad diets, and bi-chambered stomachs that accumulate indigestible items. In particular, we contend that the Bonin petrel (Pterodroma hypoleuca) is an ideal biological indicator of pelagic microplastic pollution in the Central North Pacific, due to their winter-time breeding phenology with adults provisioning chicks during winter and spring, when the subtropical convergence zone is located farther south. The goal of this study was to develop a baseline of plastic ingestion for this species, and establish necropsy and plastic quantification protocols for future monitoring. Necropsies were performed on 80 Bonin petrels collected opportunistically from Midway Atoll, to characterize (i) body condition, (ii) frequency of occurrence (FO) and loads (mass) of different plastic types, and (iii) the size and polymer composition of ingested plastic. Overall, 98% of hatch-year birds had ingested plastic (n=40), with 90% and 68% contained plastic in the gizzard and the proventriculus, respectively. Fragments (FO = 85%, average mass = 0.0099 g ± 0.0177 S.D.) and line (FO = 93%, average mass = 0.0041 g ± 0.0074 S.D.) were the most commonly ingested. Overall, 95% of after-hatch-year birds had ingested plastic (n = 40), with 93% and 25% containing plastic in the gizzard and the proventriculus, respectively. Fragments (FO = 68%, average mass = 0.0058 g ± 0.0128 S.D.) and line (FO = 83%, average mass = 0.0017 g ± 0.0017 S.D.) were the most commonly ingested plastic types. Overall, there was more plastic in the gizzard than the proventriculus as well as more plastic in hatch-year birds compared to after-hatch-year birds, expressing the need to keep these factors separate to avoid sampling bias. Fragments and line made up the majority of the ingested plastic types, with microplastics (< 5 mm) accounting for 54.6% of the ingested items. Ingested items were all low density, with two polymer types (polyethylene and polypropylene) accounting for 93% of the plastic mass. Altogether, these results suggest Bonin petrels consume a wide range of floating microplastics and provide insights into the types of plastic within their marine foraging region in the subtropical central North Pacific.
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Hawaii Pacific University