Marine Debris Project Final Report 2014

Figure 4. Debris density along the coastline with circle sizes proportionate to debris density for each transect at asite. Map is uncorrected for population, beach type, substrate, or other covariates.5.2 At-sea surveys for marine microplastics and other anthropogenic litterAnthropogenic litter occurs in all marine environments from coastlines to the open ocean and the seasurface to the sea floor. It is distributed according to its sources, transport by ocean currents, and the typeof plastic material, which determines whether or not it is buoyant in seawater. The best-measuredreservoir of plastic debris is that floating at the sea surface either as “macroplastics” measured by visualsurveys or “microplastics” (smaller than 5 mm in size) measured using surface-towed plankton nets. Weconducted surface trawls around the coast of Australia, between Fiji and Australia and between NewZealand and Australia (Figure 6) to estimate the density of plastics. At each survey site, nets were towed for15 minutes at 3 knots three times. More than 230 trawls were carried out in total. This allowed us todevelop a national map of sea surface plastic concentrations (Figure 7). For details regarding the findingsfrom this work, see Reisser et al. 2013, 2014; Appendices G and H).28 | Understanding the effects of marine debris on wildlife