Dutch seafloor litter monitoring in the North Sea : International Bottom Trawl Survey 2020

Abstract

The Marine Strategy Framework Directive (MSFD) requires EU Member States to develop programmes of measures that aim to achieve or maintain Good Environmental Status (GES) in European Seas. In order to be able to evaluate the quality state of marine waters on a regular basis and the effects of the measures taken, monitoring programs for MSFD descriptors and indicators have been established by the Member States. GES is defined by 11 descriptors, including Marine Litter (D10). The Dutch monitoring program for this descriptor includes the collection of data on the presence, abundance and distribution of macro litter on the seafloor. According to the Dutch program, the data on seafloor litter must be collected during statutory task fish surveys using a standardised GOV (Grand Ouverture Verticale) fishing net as part of the International Bottom Trawl Survey (IBTS), which is carried out yearly in the North Sea. This report presents the results of the seafloor litter monitoring during the IBTS of Quarter 1, 2020. Seafloor litter data have been collected annually since 2013, and the new data are presented and compared to the data collected in previous years. This is done for both the composition and the spatial distribution of the seafloor litter. The allocation of rectangles was the same as in 2019, however owing to permit issues of participating countries and extremely bad weather conditions during the survey period, the area covered by the Dutch IBTS 2020 was not as planned and deviates from the covered area in 2019 and earlier years. These deviations in the spatial coverage hampers comparisons over the years. In 2020, litter was caught in 83% of the hauls. The composition of this litter was similar to that of previous years, more than 90% of the 155 items recorded was plastic and these were mainly monofilament lines and plastic sheets. The majority of these items was, as in previous years, small (<25 cm2). The haul with the highest amount of litter items was in the south-east part of the North Sea towards the Dutch coast, with 19 separate items recorded. Due to the spatial deviation of the surveyed area in each year, and the semi-random sampling in a grid cell, it is difficult to compare the data between years. Bearing this in mind, mean and median values from this year were nearly the same as those of the previous two years, but lower than those of earlier years since recording began in 2013. It should be noted that the net used during the IBTS (GOV) is not designed to catch litter, therefore, it probably has a small chance of catching a litter item when it is present in the trawl path. Thus, the fact that these items are caught indicates that it is likely that there are many more items in the trawl path and that current values are a large underestimation of the actual litter present. Consequently, the degree of litter pollution on the seafloor is probably much larger than presented in this report. The Dutch seafloor litter monitoring results are uploaded to the ICES DATRAS database, and are used in OSPAR assessments of seafloor litter in the North Sea. Due to this aggregation of many ICES seafloor litter surveys of the North Sea, an assessment of the presence/absence and total count of seafloor litter items can probably be made in the near future for the whole North Sea area.