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MEASURING PROGRESS IN IMPLEMENTATION OF ANNEX V 219 types of plastic and other debris on the sea floor, the area covered by such materials, and any changes with time. Surveys can be conducted in a variety of ways, using trawls, submersibles, divers, side-scan sonar imaging, or underwater cameras. All these strategies are expensive and can cover but a small area of the ocean bottom. Trawl surveys appear to be the preferred as well as the least expensive strategy (Ribic et al., 1992), although the cost and efficiency of trawl and electronic surveys have not been assessed. Clearly, the trawl surveys would best be made in conjunction with the beach surveys at each site. Ribic et al. (1992) identified the variables to be considered in trawl surveys. One variable is vessel capability to tow effectively. The mesh size of the net governs the sizes of particles captured. Fluctuations in survey depth provide a sense of whether the trawl is following the bottom. Sampling Sites and Frequencies Because all plastic material within a given stretch of beach is to be both counted and collected, a beach site must be both short enough that a survey can be executed and long enough to provide suitable statistics. Amos (1993) suggests a minimum length of one kilometer. Whatever the length, a site needs to encompass the total beach area so there are no difficulties with lateral transport of debris. Sampling frequencies would be developed in line with quality control and quality assurance criteria. Quality control relates to the quality of the data itself, usually defined by statistical parameters, standard deviations, and precision. Quality assurance relates to the adequacy of the data to satisfy the goal of the project (i.e., whether the data reflect statistically valid changes with time in the flux of plastics from vessel discards to the coastal zone). Sampling frequency would depend in part on how often the physical oceanographic properties of a site change. In this as well as other aspects of sampling design, a statistician is crucial, as emphasized by both Ribic et al. (1992) and Amos (1993). The former asserts that "a statistician should be consulted at the onset of survey planning and be involved through the completion of the study." Data Collection and Management The survey team would employ multiple data units, such as site-by-site volume, weight, and number of debris articles. In addition, other information would be collected with each site visit, including current patterns, weather, and some measure of vessels transiting nearby shipping lanes. At certain sites, measures of commercial and recreational fishing intensity also could be important. Plastic containers often are imprinted with the year and even month of manufacture, country of origin, and manufacturer. Such information is extremely useful in associating the debris with a given source, such as a vessel as opposed to a
