According to a new ICM-CSIC study, more than 60% of marine litter on the Catalan coast is made up of plastic.
A study recently published in the journal Waste Management carried out by researchers from the Institut Català de Recerca per a la Governança del Mar (ICATMAR) and the Institut de Ciències del Mar (ICM-CSIC) of Barcelona has characterised the marine litter caught unintentionally by bottom trawlers along the coast of Catalonia and has evaluated the capacity of the Catalan bottom trawling fleet to extract this litter.
The results of the study reveal that marine litter appears in 97% of the catches, although its density on the seabed varies greatly depending on the area and the depth at which it is caught. Plastic is the most abundant material, accounting for more than 64% of the litter. In terms of distribution, the highest concentration of waste -about 14 kg per km2- is located on the seabed near highly urbanised areas, as is the case in the central area, which includes the city of Barcelona, where three quarters of the waste analysed is plastic.
On the other hand, the study reveals that the highest concentration of plastic -24 kg per km2- on the Catalan coast lies on the seabed near Barcelona, with wet wipes being the most abundant waste. In regards to depth, the continental shelf, the seabed closest to the coast -between 20 and 200 m deep- is the one with the highest concentration of marine litter, with an average of 12 kg per km2.
"Taking into account the results of this study and considering the total number of hours that bottom trawlers spend fishing in Catalonia, it is estimated that the fleet as a whole has the capacity to extract an average of 237 tonnes of marine litter per year," says one of the main co-authors and ICM-CSIC and ICATMAR researcher Marc Balcells.
The work has been carried out as part of the ICATMAR's programme to monitor fishery resources off the Catalan coast since 2019. The samples and data used for the analysis come from bottom trawls carried out between 2019 and 2021 at depths of between 20 and 700 m.
To prepare the study, the authors divided the Catalan coast into three zones, taking into account the main fishing ports from which bottom trawlers set sail: the northern zone, which includes the ports of Roses, Palamós and Blanes; the central zone, which includes the ports of Arenys de Mar, Barcelona and Vilanova i la Geltrú; and the southern zone, which includes the ports of Tarragona, l'Ametlla de Mar and la Ràpita. As for the classification of the waste, it was separated into metal, plastic, rubber, textile, wood and other waste, and each category was weighed separately.
A global problem
Marine litter is a global problem affecting all the world's seas and oceans. This waste, mainly of terrestrial origin, accumulates in the marine environment, where it has several adverse effects on ecosystems and the organisms that live there. Plastic, for its part, represents a particularly serious threat, as its degradation is extremely slow and can take decades or even centuries.
"The characterisation and quantification of marine litter provides essential information to understand the magnitude of the problem and, through a multidisciplinary approach that includes prevention, monitoring and removal of waste, to be able to tackle it," points out ICM-CSIC and ICATMAR researcher and co-author of the study Eve Galimany.
In the Mediterranean Sea, as it is a very enclosed basin, the presence of litter on its seabed is particularly severe. The waste that has accumulated over decades is very difficult to remove and is nowadays only regularly picked up by the nets of fishing vessels when they accidentally remove marine litter while fishing with their gear. For this reason, bottom trawling fleets are considered a key player in the implementation of strategies known as Fishing for Litter (FFL).
FFL strategies aim to reduce marine litter by involving one of the stakeholders affected by this problem, the fishing sector. Beyond the obvious benefits that the collection of litter by fishing vessels can bring in terms of cleaning up the seabed, which would not otherwise occur, FFL strategies can help establish links between fishers and the various administrations, and strengthen cooperation between the fishing sector and the scientific community.