SEAwise Report on the pressure induced by fisheries related litter on key species groups.
The SEAwise project works to deliver a fully operational tool that will allow fishers, managers, and policy makers to easily apply Ecosystem Based Fisheries Management (EBFM) in their own fisheries. This report provides analyses of the amount of litter on the seafloor using statistical models of trawl survey data on the number and mass of litter items per km2 in different categories. New statistical methods are implemented to estimate the temporal development, the spatial distribution, the overlap of litter with key fish species and their relationship with the spatial distribution of fishing effort. In addition to the traditional categories of litter, new indicators of the amount of litter types of ingestible sizes and litter posing a risk of entanglement were also developed. The analyses were conducted for the Baltic Sea, the North East Atlantic, Irish Waters, the South Adriatic Sea and the Eastern Ionian Sea.
Plastic, Single Use Plastic (SUP) and fishing-related litter are ubiquitous with encounter probabilities between 40% and 90% in the North East Atlantic and the Baltic Sea. Lower encounter probabilities were recorded for glass, metal, rubber, and other litter categories with the highest probabilities below 20% (40% for natural litter). Plastic, SUP, rubber, other and fishing-related litter increased steeply in both occurrence and numbers over the sampled 10 years. In 2012, around 20 plastic and 10 fishing related litter items were detected per km2 in the North East Atlantic whereas in the last sampling year, these categories had increased to around 35 plastic and 22 fishing-related items, almost doubling in the 10 sampled years in both categories. A similar rate of increase was seen in litter posing entanglement risk and ingestable litter. Ingestable litter and litter posing a risk of entanglement occurred in the greatest numbers in coastal areas off Germany, Belgium, Holland, France and Spain and along the shelf edge in the Bay of Biscay.
Most of the categories of litter in Irish Waters showed a general increase over the study period in the number of litter items/km2 indices. The positive trends were strongest in plastic, rubber and fishing related litter.
In the Bay of Biscay, plastic, fishing related, natural and SUP are the most predominant categories in terms of number of items.
Plastic did not increase significantly over the sampling period in the South Adriatic, whereas number of items of fishing related litter did. SUP and fishing related litter were concentrated inshore. The distribution of fishing related litter and the commercial species European hake and red mullet showed a high degree of high overlap. Plastic was the dominant category in mass and number in the Eastern Ionian Sea in all sampled years. Some sites (Kerkiraikos Gulf, close to Corfù Island) were identified as possible sink areas with high seafloor litter density. These areas are enclosed and exposed to intense marine traffic, river outflow, fishing, and tourism that may be also linked to increased marine litter accumulation.
Across areas, modelling trawl and beam-trawl survey data proved very useful to capture and compare spatial and temporal trends of different categories of marine macrolitter. Plastic followed by the subcategory SUP dominated the observations from the surveys in all areas. In the Mediterranean, plastic and SUP reached higher number of items and mass compared to the NE Atlantic, Irish Waters and the Baltic Sea, whilst the abundance of fishing related litter was comparable in all the areas. The overlap analysis demonstrated some degree of overlap between effort footprint and fishing litter distribution, but poor correlations were also observed. This might be caused by the sinking, accumulation and transport of marine litter beyond the source areas. However, an increase in fishing effort is likely to increase the annual load of fishing related litter in the medium to long term. The analyses provide useful information on trends and accumulation areas among the areas where bottom trawling can occur.
