A trawl survey of seafloor macrolitter on the South African continental shelf.

Demersal trawls provide an index of seafloor macrolitter abundance, but there are no published data from sub-Saharan Africa. We collected litter items from 235 trawls conducted to assess fish abundance off South Africa. Only 17% of trawls contained litter (3.4 items·km⁻², 2.1 kg·km⁻² but only 0.2 kg·km⁻² excluding four megalitter items). Plastic items predominated (88%), of which 77% floated once cleaned of epibionts. One LDPE bag manufactured three months before being caught carried pelagic goose barnacles Lepas anserifera , confirming that biofouling leads to rapid sinking of floating plastics. Fishery/shipping wastes comprised 22% of litter items (98% by mass; 73% excluding megalitter items); the remainder was general waste – mostly packaging or other single-use items – that could come from land- or ship-based sources. Litter was more abundant in deep water close to Cape Town. The annual demersal trawl survey is a useful way to monitor seafloor litter off South Africa. • We report the first estimates of seabed litter from trawl surveys off sub-Saharan Africa. • Only 17% of trawls contained litter, and densities were low (3.4 items·km⁻²). • Most litter was packaging, but marine wastes accounted for most of the mass of litter. • Proximity to Cape Town, a major urban litter source, best explained litter distribution • Most plastic items floated, and biofouling probably caused these plastic items to sink. [ABSTRACT FROM AUTHOR]