Elasmobranchs as bioindicators? A comparative study on ingestion of plastics in the Nordic region

Abstract

Plastic pollution has become a major threat to many marine ecosystems, and there is a need for an improved understanding of its impact on marine organisms. Studies have mainly focused on lower trophic levels, including species occurring in the north, since they can be highly vulnerable to plastic pollutants. However, no studies have yet focused on elasmobranchs which belong to the highest trophic levels, in Nordic waters, and how they can provide important data for the monitoring of plastic pollutants. Elasmobranchs from other regions have been described as good bioindicators due to their propensity to bioaccumulation and biomagnification. This study aimed at quantifying and characterizing the ingested macroplastic particles above 1 mm in the stomachs of three elasmobranch species: one shark, the spurdog (Squalus acanthias) and two skate species the starry ray (Amblyraja radiata) and the Arctic skate (Amblyraja hyperborea) from the North Sea, the Norwegian Sea and the Barents Sea. Stomachs were digested with 10% KOH and the remaining particles were size-selectively filtered. Analysis of 229 stomach samples revealed only one plastic particle. This is in stark contrast to what has been previously reported for elasmobranchs in southern waters. Published models predicted a low likelihood for macroplastics in polar waters, nonetheless the expectation for this study was to find a substantially higher abundance of plastic particles in the target species than observed. For 27 individuals the spiral valves were also analyzed for comparison, but no plastics were found. Considering the rising amount of plastics released into the environment, it is very likely that especially top elasmobranch predators, especially in the Arctic, will be affected in the near future. We therefore highly advise further ecological and environmental studies on elasmobranchs, their role in regional food webs and the impact of pollutants on them and the entire connected ecosystems.