Abstract
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 non-synthetic man-made litter. However, we show that when a dedicated standard protocol for the detection of litter is followed, a considerably higher percentage (15% of 81 harbour 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 other non-food remains like stones, shells, bog-wood, etc., suggesting that litter was often ingested accidentally when the animals foraged close to the bottom. Most items 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 higher levels 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 harbour porpoises 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 longer-term comparisons 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.
Highlights
The wide distribution and abundance of man-made litter, in particular plastics, has been signalled as a major threat to the oceans (UNEP 2011, 2014; CBD 2016) which affects a broad range of marine organisms through entanglement and ingestion (Kuhn et al 2015)
Marine litter has long been an important issue in the Oslo-Paris Convention for the Protection of the Marine Environment of the NorthEast Atlantic (OSPAR) and more recently has become strongly embedded in European Union (EU) policy
Stomachs of 654 harbour porpoises found dead on the Dutch coast between 2003 and 2013 were analysed (Table 1); two necropsied individuals were from year 2003, 268 from years 2005 to 2009 and 384 from years 2010 to 2014
Summary
The wide distribution and abundance of man-made litter, in particular plastics, has been signalled as a major threat to the oceans (UNEP 2011, 2014; CBD 2016) which affects a broad range of marine organisms through entanglement and ingestion (Kuhn et al 2015). Among the many environmental aspects of MSFD aiming at ecological conservation and sustainable use of marine resources, ‘Descriptor 10’ addresses marine litter, in which GES is defined as the situation where ‘‘marine litter does not cause harm to the coastal and marine environment’’. How this should be interpreted and dealt with in terms of assessments is being addressed further by a specialist group (Galgani et al 2010; MSFD-TSGML 2011, 2013; Werner et al 2016), and regional planning in order to achieve GES is underway (e.g. OSPAR 2014).
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