Density of the floating litter offshore

Floating litter was counted during ship-based bird surveys in the Belgian part of the North Sea. The study aimed to develop a methodology to determine densities of floating litter. On the 2200 km² covered by the survey from February 2009 to July 2010 in total 741 pieces of debris were spotted, 80% of those being plastic items. As the debris are difficult to detect far away from the boat a correction factor was applied, this means that 1449 items should have been spotted of which 1176 were plastic. The density of debris (0.66 items per km²) and of plastic (0.53 items per km²), those densities are respectively similar to the densities of Razorbills and Common Scoter. In other words, the Belgian part of the North Sea contains as many floating particles as there is Scoters swimming around.

The floating litter was grouped in similar categories as the plastic ingested. The result of this classification was that almost 60% of the floating elements were sheet like plastic: plastic bags and foils. One fifth is hard plastics: plastic bottles, cans, buoy, plastic cups, fishing box….10% of the observed floating items were inflated party balloons. The party balloons are the perfect example of the harm caused by plastic pollution because they are both found in the stomachs of Northern Fulmars and the ribbon that attach them is also entangling the birds.

It can be concluded that the methodology used to count seabirds is suitable to for simultaneous counts of floating plastics, although the smallest plastic items, the ones that are ingested by birds, could not be perceived by this technique.

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