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MEASURING PROGRESS IN IMPLEMENTATION OF ANNEX V 217 indication of whether the harm is abating. It is important to remember, however, that the fur seals are studied on land only, so the results may not reflect the total effects of marine debris, and that the case for population-level effects on these animals, whale the strongest data available, is only circumstantial. One group of researchers has recommended that all future studies of wildlife interactions with debris include statistically adequate sampling schemes designed to test hypotheses that the prevalence of debris is either increasing or decreasing in given areas or for specific taxa (Sileo, 1990). Monitoring Plastics in the Marine Environment As discussed in Chapter 2, plastics are the most abundant and most harmful type of marine debris. Their persistence in the marine environment is virtually infinite, according to some environmental scientists, and the solids can cause considerable harm in addition to aesthetic insults. Plastics can kill marine animals through ingestion or entanglement and inflict costly damage to vessel operations through fouling of propellers, water intake pipes, and fishing gear. Another threat may lie in the accumulation of plastics on the sea floor. Although plastics are buoyant when introduced to the marine environment, they quickly sink to the bottom, where they may inhibit gas exchange between the overlying waters and the pore waters of the sediments. Hypoxia or anoxia could result. Therefore, for purely ecological reasons, it would be advisable to conduct long-term monitoring programs to measure amounts of plastics in the marine environment, both on beaches and on the coastal sea floor. The data also could provide a measure of progress in Annex V implementation, because plastic is the one material for which all overboard discharge is banned. The committee, drawing on the personal experience of several members and relying heavily on Ribic et al. (1992) and Amos (1993), devised a basic monitoring strategy that would be useful from both an Annex V and a scientific standpoint and therefore make the best possible use of resources. The strategy borrows from the basic methodology of the EPA's planned marine debris monitoring program but is different in three important respects: The committee's model focuses on plastics rather than all marine debris, attempts to isolate vessel garbage from land- source debris, and includes both beach and benthic surveys. The goal would be to determine the fluxes of plastics through the marine environment as a function of time. The focus could be expanded to include other particularly harmful and problematic debris items, such as fishing gear. It might be appropriate to incorporate such an effort into NOAA's Status and Trends Program, which has been described as ''the closest current approach to a standardized national assessment of marine pollution'' (National Research Council, 1990). The NOAA program measures contaminants such as metals and chlorinated hydrocarbons at over 100 sites on an annual basis. Bottom-feeding fish, mussels, oysters, and sediments are collected. The goal is "to create, maintain,