Monitoring of seafloor litter on the Dutch continental shelf : International Bottom Trawl Survey 2021, Dutch Beam 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 status 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. The Dutch monitoring program for Marine Litter (D10) 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. Anthropogenic pollution of our oceans, including marine litter, threatens wildlife, hinders human activities and reduces the recreational value of our coasts. Marine litter affects all groups of marine wildlife through effects such as entanglement and ingestion. Various initiatives to reduce litter in the (marine) environment have recently been started or are currently under discussion. Despite management measures to decrease the input of litter and to remove litter from the environment, litter remains on the seafloor. This report presents the seafloor litter composition, abundance and spatial distribution based upon catches of the regular fish surveys, the International Bottom Trawl Survey (IBTS) and the Dutch Beam Trawl Survey (BTS). Only the catches on the Dutch Continental Shelf (DCS) are used. To assess the status of seafloor litter on the DCS, the Dutch data are supplemented with those from international partners surveying the DCS within the IBTS.The seafloor litter catches on the DCS consisted mainly of plastic items: 88% (BTS) and 95% (IBTS) of the litter items found were made of plastic. Monofilaments, plastic sheets and various types of (plastic) ropes/lines were the most commonly caught litter types. A mean density of 165 (IBTS) and 201 (BTS) litter items per km 2 was calculated on the DCS, with mean values per ICES rectangle exceeding 200 items per km 2 . It should be noted that the net used during the IBTS (GOV) and BTS (beam trawl) is not designed to catch litter. For the GOV, the catchability of many benthic species is assumed to be less than 5%, the chance of catching a litter item when it is present in the trawl path is likely to be even smaller than 5%. The fact that these items are caught thus indicates that it is plausible that there are many more litter items in the trawl path and that current values are a large underestimation of the actual litter present. On top of that, due to the selectivity of the fishing gears used in the surveys, only a selection of the types of litter items present retain in the net. This is reflected by the fact that hardly any (small) single-use plastics were caught. However, by including the BTS survey a slightly more repre...

Monitoring of seafloor litter on the Dutch continental shelf : International Bottom Trawl Survey 2022, Dutch Beam Trawl Survey 2021

“…The Dutch BTS 2021 Q3 performed 142 valid hauls, of which 38 were conducted on the Dutch continental shelf. As presented in Figure 2.2, the planned area and amount of hauls per ICES rectangle for 2021 remained generally unchanged compared to those of previous years (Volwater & van Hal 2021). The executed hauls and spatial distribution of litter caught during the Dutch BTS 2021 are presented in Figure 3.6.…”

“…Annex 2 Quality -Outlier check 2.1 IBTS Marine litter data from the international IBTS partners was obtained from ICES DATRAS. A data analyses determining the data to be used was done in Volwater & van Hal (2021). It was concluded that Dutch count data was available from 2013 on, French and German count data from 2015 and Danish count data only from 2021 on.…”

Mosdiertjes problematiek in Nederlandse kustwateren : onderzoek naar de verspreiding voor de Nederlandse kust en de problemen die het veroorzaakt in de visserij en mogelijke mitigerende maatregelen

“…Aangroeisel op het afval, waaronder mosdiertjes, wordt ook genoteerd. De verzamelingsmethodiek voor het zwerfvuil staat beschreven inVolwater et al (2021).…”