Plastic ingestion by harbour porpoises Phocoena phocoena in the Netherlands: Establishing a standardised method

• Published in: Ambio
• Main Authors: van Franeker, Jan A., Bravo Rebolledo, Elisa L., Hesse, Eileen, IJsseldijk, Lonneke L., Kühn, Susanne, Leopold, Mardik, Mielke, Lara
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: MSFD; North Sea; Phocoena phocoena; Plastic ingestion; harbour porpoise; marine litter monitoring; marine strategy framework directive; Harbour porpoise
• Online Access: https://research.wur.nl/en/publications/plastic-ingestion-by-harbour-porpoises-phocoena-phocoena-in-the-n; https://doi.org/10.1007/s13280-017-1002-y

Stomach contents of harbour porpoises (Phocoena phocoena) collected in the Netherlands between 2003 and 2013 were inspected for the presence of plastic and other man-made litter. In 654 stomach samples the frequency of occurrence of plastic litter was 7% with less than 0.5% additional presence of nonsyntheticman-made litter. However, we show that when a dedicated standard protocol for the detection of litter is followed, a considerably higher percentage (15% of 81harbour porpoise stomachs from the period 2010–2013) contained plastic litter. Results thus strongly depended on methods used and time period considered. Occurrence of litter in the stomach was correlated to the presence of othernon-food remains like stones, shells, bog-wood, etc., suggesting that litter was often ingested accidentally when the animals foraged close to the bottom. Mostitems were small and were not considered to have had a major health impact. No evident differences in ingestion were found between sexes or age groups, with the exception that neonates contained no litter. Polyethylene and polypropylene were the most common plastic types encountered. Compared to earlier literature on the harbour porpoise and related species, our results suggest higherlevels of ingestion of litter. This is largely due to the lack of dedicated protocols to investigate marine litter ingestion in previous studies. Still, the low frequency of ingestion, and minor number and mass of litter items found in harbourporpoises in the relatively polluted southern North Sea indicates that the species is not a strong candidate for annual monitoring of marine litter trends under the EU marine strategy framework directive. However, for longertermcomparisons and regional differences, with proper dedicated protocols applied, the harbour porpoise has specific use in quantifying litter presence in the, for that specific objective, poorly studied benthic marine habitat.