Sea floor litter monitoring : International Bottom Trawl Survey 2016

Abstract

The Marine Strategy Framework Directive (MSFD) requires the European Member States to develop programmes of measures to achieve or maintain Good Environmental Status (GES) in European Seas. To be able to evaluate the quality state of the marine waters on a regular basis and the effect of measures taken, monitoring programs for MSFD descriptors and indicators have been established by the Member states. GES is described by 11 descriptors, and marine litter is one of them. The Dutch monitoring program for this descriptor includes amongst others the collection of data on the presence, abundance and distribution of litter on the seafloor. According to the Dutch program, the data on seafloor litter must be collected by statutory task fish surveys using standardized GOV fishing net, as a part of the International Bottom Trawl Survey (IBTS). This report presents the results of the seafloor litter monitoring during the IBTS survey of Quarter 1 2016. Seafloor litter data is collected annually during this survey since 2013, and the new data is presented in perspective of the data collected in previous years. This is done for the composition and the spatial distribution of the seafloor litter from the catch. The composition of the litter collected in 2016 is similar compared to earlier years; plastic and specifically rope/lines are the most dominant litter items found. The survey was again carried out on board the UK vessel CEFAS Endeavour, and the standard Dutch IBTS area including the Channel area was covered. Even though, due to a survey design based on random sampling within ICES rectangles, comparison in spatial distribution of litter as well as in estimates of the amount of litter between years is difficult. The spatial distribution of the litter seems random with small and large catches close to each other. It might be a result of small probability of actually catching litter items with a GOV trawl not designed for this purpose, or by differences in seafloor structure. It is possible to register additional habitat information and use this information in the data analysis After four years of litter sampling as part of the IBTS, inconsistencies in categorising the litter items are still found between national observers. In 2015 and 2016, close cooperation with CEFAS staff showed that these inconsistencies also exist between countries. The inconsistencies exist for a small number of subcategories, for which there is some arbitrary in how to divide items between them. Analysing the Dutch IBTS data by itself indicates a number of limitations, e.g. the spatial differences owing to a semi-randomized survey design between years, which could be overcome by combining the international data of the IBTS. This data can be found in the database developed and accessible via the ICES datacentre and combining the data is done within OSPAR.