Microplastic ingestion by Atlantic mackerel and blue whiting in Icelandic waters

Since 1950s, plastics have been extensively used in a wide variety of products both in industries and private households. Unfortunately, some plastic litter ends up in the marine environment where it fragments into smaller particles and finally into microplastics (0.01-5mm). Microplastics are present in sediments and the water column where they can be ingested by marine organisms. This study investigates the microplastic occurrence in Atlantic mackerel (Scomber scombrus), a pelagic species, and blue whiting(Micromesistius poutassou), a mesopelagic species, in Icelandic waters. Both species are commercially important. The gastrointestinal tracts of 50 Atlantic mackerel and 40 blue whiting, sampled northeast and south of Iceland in July 2019 and 2020, were processed with an alkaline digestion method, filtered, and visually inspected with a stereomicroscope. Observed microplastic particles were further analysed with Raman spectroscopy in order to identify their polymer types. Due to the high risk of fibre contamination in microplastic research, the occurrences were presented both including and excluding fibres. The microplastic occurrences were 12.0% and 6.0% including/excluding fibres for Atlantic mackerel and 7.5% and 2.5% for blue whiting. The average number of particles among the individuals that had ingested microplastics were 1.3 particles/individual for Atlantic mackerel and 1.0 particles/individual for blue whiting. This study adds to existing evidence that microplastics are eaten by epi- and mesopelagic fish species and provides the first record of microplastic occurrence in Atlantic mackerel and blue whiting in Icelandic waters.