Birds of a feather eat plastic together: high levels of plastic ingestion in Great Shearwater adults and juveniles across their annual migratory cycle.

Gwenyth Emery,Lindsay Agvent,Kevin D. Powers,Rainer Lohmann,Gina Shield,Vonica Perold,Johanna Pedersen,Christine A. Hudak,David N. Wiley,Justin J. Suca,Michael A. Thompson,Leandro Bugoni,Peter G. Ryan,Michael J. Moore,Trevor Glass,Anna R. Robuck,Craig A. Harms

doi:10.3389/fmars.2021.719721

Abstract

Limited work to date has examined plastic ingestion in highly migratory seabirds like Great Shearwaters (Ardenna gravis) across the their entire migratory range, although this species is prone to ingest plastic as a wide-ranging procellariiform. We examined 217 Great Shearwaters obtained from 2008-2019 at multiple locations spanning their yearly migration cycle across the Northwest and South Atlantic to assess accumulation of ingested plastic as well as trends over time and between locations. A total of 2,328 plastic fragments were documented in the ventriculus portion of the gastrointestinal tract, with an average of 9 plastic fragments per bird. The mass, count, and frequency of plastic occurrence (FO) varied by location, with higher plastic burdens but lower FO in South Atlantic individuals from the breeding colonies. No fragments of the same size or morphology were found in the primary forage fish prey, the sand lance, (Ammodytes spp., n = 202) that supports Great Shearwaters in Massachusetts Bay, USA, suggesting the birds directly ingest the bulk of their plastic loads rather than accumulating via trophic transfer. Fourier-transform infrared spectroscopy indicated that low- and high-density polyethylene were the most common polymers ingested, within all years and locations. Individuals from the South Atlantic contained a higher proportion of larger plastic items and fragments compared to juveniles and non-breeding adults from the NW Atlantic, possibly due to increased use of remote, pelagic areas subject to reduced inputs of smaller, more diverse, and potentially less buoyant plastics found adjacent to coastal margins. Different signatures of polymer type, size, and category between similar life stages at different locations suggests rapid turnover of ingested plastics commensurate with migratory stage and location, though more empirical evidence is needed to ground-truth this hypothesis. This work is the first to comprehensively measure the accumulation of ingested plastics by Great Shearwaters over the last decade and across multiple locations spanning their yearly trans-equatorial migration cycle, and underscores their utility as sentinels of plastic pollution in Atlantic ecosystems.

Highlights

An estimated 5 to 125 trillion pieces of plastic greater than 100 μm in size are buoyant within the ocean surface layer, where these items are subject to oceanic scale circulation and varied biophysical interactions (Eriksen et al, 2014; Lindeque et al, 2020)
Out of 2328 plastic-like items found in the ventriculus of 217 Great Shearwaters, 2121 items were assessed via Fourier transform infrared spectroscopy (FTIR), and 2035 items (95.9%) were confirmed as plastic via FTIR; the mean FTIR confidence score of identification was 96.8%
Frequency of occurrence (FO) of ingested plastic varied by location, sampling year, and age of birds, with the lowest FO observed in breeding phase individuals from Gough and Nightingale Island (∼60% in adults and 58% in chicks, respectively), ranging up to 100% in the NW Atlantic and off the coast of Brazil (Table 1)

Summary

Introduction

An estimated 5 to 125 trillion pieces of plastic greater than 100 μm in size are buoyant within the ocean surface layer, where these items are subject to oceanic scale circulation and varied biophysical interactions (Eriksen et al, 2014; Lindeque et al, 2020). Metaanalysis efforts conducted by Wilcox et al (2015) found that 59% of seabird species examined between 1962 and 2012 had ingested plastic, and, within those studies, on average 29% of individuals had plastic in their gastrointestinal tract (Ryan et al, 2009; Wilcox et al, 2015). In the Atlantic basin, Great Shearwaters (Ardenna gravis) have been found to ingest plastic at high rates for decades, with multiple studies documenting 70–95% ingestion rates by the species, sampled within their breeding or non-breeding ranges (Furness, 1983, 1985; Ryan, 1987a,b, 2008; Bond et al, 2014). Several studies have noted a lower frequency of plastic ingestion in this species, ranging from 0–39% frequency of ingestion (Brown, 1981; Ryan, 2008; Haman et al, 2013; Bond et al, 2014)

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