flotsam, such as trees washed out to sea, and focuses on nondegradable synthetic materials that persist in the marine environment. Not all of these materials are inherently harmful, but evidence of damaging effects provides the impetus for this report, which focuses on measures to prevent and reduce the debris, particularly plastic debris, which has persistent negative impacts. It is also important to note that different types of marine debris have different effects. For example, a derelict net that is still actively ghost fishing raises concerns about entanglement of marine life, whereas a plastic water bottle discarded at sea may wash ashore and become a visual disamenity. As discussed in the following chapters, an improved understanding of the fates and impacts of various marine debris types will improve our efforts to prioritize mitigation.
Marine debris has many sources. Overall, most debris comes from land-based sources (e.g., household garbage, medical waste, plastic resin pellets used as inputs for plastics manufacturing), but a considerable amount of debris is discharged at sea3 (e.g., U.S. Commission on Ocean Policy, 2004; Sheavly, 2007). Ocean-based sources of debris (e.g., fishing gear; galley waste; dunnage; cargo nets; wastes generated by offshore minerals and petroleum exploration, development, and extraction) may come from a diverse fleet of vessels and platforms. A 1995 National Research Council (NRC) report characterized 10 distinct U.S. maritime sectors: recreational boats; commercial fisheries; cargo ships; passenger day boats and ferries; small public vessels4; offshore platforms, rigs, and supply vessels; U.S. Navy combatant surface vessels; passenger cruise ships; research vessels; and miscellaneous vessels (National Research Council, 1995a). There are considerable differences between these sectors (e.g., number of vessels, average vessel size, average crew or passenger size, average time spent at sea), which can result in differences in garbage generation and waste management capabilities. In addition, these sectors are not static and there may be a great deal of variability within vessels of a single sector (see Box 1.1). Measures aimed at preventing and reducing marine debris will need to be tailored to the characteristics of each sector (National Research Council, 1995a).
Similarly, studies have shown significant regional differences in marine debris sources, abundance, impacts, and trends related to such factors as geographical location, oceanographic conditions, and proximity
to the Marine Debris Research, Prevention, and Reduction Act (33 U.S.C. § 1951 et seq.) (“Definition of Marine Debris for Purposes of the Marine Debris Research, Prevention, and Pollution Act,” 73 Fed. Reg. 30322 [May 27, 2008]).