Indigo-dyed cellulose fibers and synthetic polymers in surface-feeding seabird chick regurgitates from the Gulf of Alaska

We provide evidence of anthropogenic materials ingestion in seabirds from a remote oceanic area, using regurgitates obtained from black-legged kittiwake (Rissa tridactyla) chicks from Middleton Island (Gulf of Alaska, USA). By means of GPS tracking of breeding adults, we identified foraging grounds where anthropogenic materials were most likely ingested. They were mainly located within the continental shelf of the Gulf of Alaska and near the Alaskan coastline. Anthropogenic cellulose fibers showed a high prevalence (85 % occurrence), whereas synthetic polymers (in the micro- and mesoplastics dimensional range) were less frequent (20 %). Most fibers (60 %) were blue and we confirmed the presence of indigo-dyed cellulosic fibers, characteristic of denim fabrics. In terms of mass, contamination levels were 0.077 μg g^-1 wet weight and 0.009 μg g^-1 wet weight for anthropogenic microfibers and synthetic polymers, respectively. These results represent the only recent report of contamination by anthropogenic fibers in seabirds from the Gulf of Alaska.