Marine debris in the digestive tract of a trans-hemispheric migratory pelagic seabird wintering in Argentine waters

In this work, the digestive tracts of 30 Great Shearwaters (Ardenna gravis) stranded along the coast of northern Argentine Patagonia were investigated for the issue of marine debris ingestion. Such debris was found in all sampled shearwaters, with a total of 409 particles, of which plastic was the sole category recovered. The bulk of these debris was found in the gizzard. The average number of plastic items per bird (stomach chambers combined) was 13.63 items (range = 0-50), with a mean mass estimated at 0.38 ± 0.38 g. Over half of the ingested plastic items were classified as meso-plastics (5-25 mm), followed by micro-plastics (<5 mm). Debris items pertained to nine polymer categories, though polyethylene prevailed followed to a lesser extent only by polypropylene. The frequency of debris occurrence was 100% for the gizzard (mean: 12.20 ± 13.08 pieces/bird; range: 1-50) and 46.6% for the proventriculus (mean: 3.07 ± 5.01 pieces/bird; range: 0-20). The amount of debris in the gizzard was significantly higher in individuals that also presented debris in the proventriculus. The amounts and mass of both meso- and micro-plastics were significantly higher in the gizzard than in the proventriculus. The same result applies to the amounts and mass of both industrial and user plastics, and the amounts and mass of both PE and PP (and the abundance of PA). Our results reveal pervasive plastic ingestion in the Great Shearwater and contribute to baseline information for monitoring marine debris impacts in the Southwestern Atlantic.