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Tackling Marine Debris in the 21st Century 2 Understanding Marine Debris and Its Impacts Marine debris presents a significant environmental challenge, far more diverse and less tractable than most other environmental issues. Marine debris, especially plastic debris, is now ubiquitous in the oceans and along coasts. It is found in the middle of the oceans (Matsumura and Nasu, 1997), on remote uninhabited tropical atolls (Donohue et al., 2001; McDermid and McMullen, 2004; Morishige et al., 2007), and on Arctic and sub-Antarctic islands (Gregory and Ryan, 1997). Despite heightened awareness of the problem and ongoing remediation efforts, studies suggest that, overall, marine debris in the environment has not been reduced (Miller and Jones, 2003; Barnes, 2005; Sheavly, 2007; Yamashita and Tanimura, 2007). This chapter provides evidence for why marine debris is a serious and challenging problem. The body of work addressing marine debris is voluminous and an exhaustive literature review was not possible and not explicitly or implicitly part of the committee’s statement of task. Instead, the committee summarizes selected peer-reviewed literature illustrating the prevalence and impacts of marine debris in the environment (see Appendix C) and assesses the effectiveness of measures to prevent and reduce marine debris based on this information. Knowledge gaps are identified and recommendations provided on key aspects of monitoring and research that can help improve assessments and prioritize marine debris mitigation efforts. Much remains to be learned about marine debris sources, amounts, and impacts that will enhance efforts to reduce, prevent, and mitigate
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Tackling Marine Debris in the 21st Century marine debris; however, existing information about marine debris and its impacts is sufficient to support immediate action to arrest this global environmental problem. ABUNDANCE AND FLUX For many people, the term “marine debris” evokes images of litter strewn on a beach, such as the one shown in Figure 2.1, but marine debris is much more than beach litter. Debris is found throughout the marine environment, from coastal waters to the deep ocean and from the sea surface down to the benthos (Figure 2.2). Monitoring is a primary mechanism for identifying sources; for understanding temporal and spatial trends in debris composition, prevalence, and distribution; and, therefore, for understanding the extent of the problem and the effectiveness of efforts to address it. The vastness of the world’s oceans makes estimating the total amount of marine debris a significant challenge; nonetheless, the number and geographic coverage of studies carried out so far (see Appendix C, Tables I–III) highlight the worldwide pervasiveness of marine debris. Coastal Environments Coastal areas have served as the primary focal point for marine debris awareness and mitigation and remain hotspots of marine debris accumulation. Debris of both terrestrial and maritime origins converges and is concentrated at the land–sea interface. Because of the visibility of the problem, more is known about the occurrence and impact of marine debris along coastlines than in any other marine environment. The prevalence of shoreline debris deposits is summarized in Appendix C, Table I. Marine debris items range from 4 to more than 48,000 items per kilometer (km) of shoreline, while the weight of the items ranges from 31 grams per km to more than 3.8 metric tons per km. Plastic materials dominate coastal marine debris in number, volume, and weight at all debris sizes examined to date, particularly on beaches and areas near population centers (e.g., Ribic et al., 1997; Sheavly, 2007). Because of the variation in methods used (e.g., data collected along transects from the waterline to the “edge” of the beach, along transects parallel to the shoreline, or along a strandline where debris is likely to be highest), straightforward comparisons among studies is problematic. The majority of studies of coastal marine debris have noted increasing quantities of debris (e.g., Merrell, 1984; Ryan and Moloney, 1993; Walker et al., 1997; Willoughby et al., 1997; Velander and Mocogni, 1998), other studies found no change over time (e.g., Lucas, 1992; Williams and Tudor, 2001; Santos et al., 2005a; Sheavly, 2007), and a few studies have docu-
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Tackling Marine Debris in the 21st Century FIGURE 2.1 Image of a typical trash-covered beach (used with permission from the National Oceanic and Atmospheric Administration).
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Tackling Marine Debris in the 21st Century FIGURE 2.2 Spot prawn and rockfish swimming around a derelict commercial trap at 250 m depth off the central California coast (used with permission from Diana Watters, National Marine Fisheries Service, Southwest Fisheries Science Center, Fisheries Ecology Division). mented decreases (e.g., Johnson, 1994; Edyvane et al., 2004). Teasing out the effects of regulatory changes in debris deposition can be difficult. For example, Johnson (1994) reported a decline in trawl webbing on a beach near Yakutat, Alaska, coincident with the implementation of the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 (MARPOL) Annex V. However, the pre–and post–Annex V periods examined correspond to the transition from foreign to joint venture to domestic fisheries in the Gulf of Alaska. Moreover, during this same period, Gulf of Alaska groundfish catches dropped by more than 50 percent; thus, the observed decline in trawl webbing could be due to MARPOL Annex V, a change in fishing intensity, or a combination of factors. Elucidating the contribution of mitigation actions on the abundance of marine debris can only be achieved when there is an opportunity to draw on a series of compatible longitudinal surveys. In the United States, after ratification of MARPOL Annex V in 1988, efforts were made to document any changes in marine debris as indicated by accumulations on beaches. In 1989, these efforts led to the establishment
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Tackling Marine Debris in the 21st Century of the National Marine Debris Monitoring Program (NMDMP) (Sheavly, 2007). Following the congressional ratification of MARPOL Annex V and the enactment of the Marine Plastic Pollution Research and Control Act (33 U.S.C. § 1901 et seq.), an interagency workgroup (including the Environmental Protection Agency, the National Oceanic and Atmospheric Administration [NOAA], the National Park Service, and the U.S. Coast Guard) designed NMDMP. The aim of NMDMP was to evaluate the magnitude of the marine debris problem, its geographical distribution, any seasonal or long-term trends, and debris sources, and to do so according to a statistical design and sampling protocol that would allow for comparisons through time and across regions nationwide (Escardó-Boomsma et al., 1995). NMDMP used indicator items to assign debris to presumptive ocean- or land-based sources, as well as to quantify items of particular concern. The Center for Marine Conservation (now known as The Ocean Conservancy) conducted the monitoring from 1996 to 2006 (data used for the five-year national analysis was collected from 2001 to 2006) and released their findings in a 2007 report (Sheavly, 2007). The study shows that, for the nation as a whole, there has been no statistically significant change in the prevalence of marine debris. Of the nine regions surveyed, only the Hawaiian Islands showed a significant decrease, and the effects of El Niño may have been a contributing factor (see Sheavly  for a detailed summary of results). That is, NMDMP results indicate that the accumulation of litter on the nation’s beaches is not diminishing. Pelagic Environments Since Heyerdahl’s (1970) report on the occurrence of marine debris in the open ocean, a growing number of studies have provided a greater but incomplete understanding of the problem. These studies reveal that estimates of marine debris in the near-surface zone are highly variable, encompassing five orders of magnitude from less than 1 item per square km to as many as 332,556 items (about 5 kg) per square km (see Appendix C, Table II). Reported variability in debris prevalence likely reflects differences in sampling techniques, total area sampled, geographic locations, sea states, and timing of the sampling exercises, as well as non-uniformities in the distribution of debris. For instance, studies using nets to sample pelagic debris have employed net mesh sizes ranging from 150 to 947 μm, whereas visual shipboard surveys have detection limits on the order of several centimeters. Selection of monitoring areas also has a clear impact on sampling results. The comparatively high density of marine debris documented by Moore et al. (2001a) reflects the selective sampling of an ocean surface convergence zone where debris is
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Tackling Marine Debris in the 21st Century known to accumulate (Matsumura and Nasu, 1997; Pichel et al., 2007). Similarly, work by Yamashita and Tanimura (2007) revealed an extremely patchy distribution of plastic pellets in the Pacific Ocean near Japan. One sampling tow showed upwards of 174,355 items per square km, whereas 21 of 76 tows (28 percent) contained no plastic pellets whatsoever. Because these studies did not examine pelagic debris distributions before and after implementation of MARPOL Annex V, there is no information to determine if MARPOL Annex V has contributed to demonstrable changes in the prevalence of pelagic marine debris. Benthic Environments Although less readily observed than marine debris in coastal or pelagic environments, marine debris is also present on the sea floor (see Appendix C, Table III). However, given the difficulties of sampling benthic environments, there have only been a small number of studies of benthic debris and those noted herein have focused on areas that are shallower than several hundred meters in depth. Generally, these studies show that benthic debris density is positively correlated with proximity to human activity (i.e., greater debris density nearshore vs. offshore). For instance, submerged areas adjacent to beaches in Curaçao (Nagelkerken et al., 2001) and Indonesia (Uneputty and Evans, 1997) have the two highest reported densities of benthic marine debris. However, distance from large population centers does not provide a uniform guarantee of low debris levels; Donohue et al. (2001) documented the presence of marine debris in shallow waters of the uninhabited islands of the Northwestern Hawaiian Islands (NWHI) and concluded that fishing gear fouling the benthos of these islands originated from distant water fisheries. Debris Fluxes Buoyant materials introduced at sea are either entrained along convergence zones or move toward shore, albeit over long time scales, from years to decades (Kubota, 1994; Donohue, 2005; Pichel et al., 2007). Floating marine debris is known to form dynamic patches and aggregations, at least in the Pacific Ocean (Kubota, 1994; Ingraham and Ebbesmeyer, 2001; Kubota et al., 2005). Storms and spring tides have been observed to uncover and resuspend debris that has been incorporated into shoreline sediments (Johnson and Eiler, 1999). The rate at which debris in the open ocean is entrained toward the shoreline, and the frequency with which debris is moved from the shoreline into the open seas and redeposited on the shore, is poorly understood (see National Research Council [1995a] for discussion). Anecdotal evidence from debris cleanup activi-
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Tackling Marine Debris in the 21st Century ties suggests that debris may remain in the pelagic realm for extended periods. Understanding these lag processes is an important element in predicting the amount of time that may be required to detect changes in the quantity of debris introduced into the marine environment and thus the effectiveness of management measures intended to reduce debris discharges. An area that has received little attention is the understanding of factors that affect and promote the vertical transport of debris. While the fates of dense materials (e.g., metal, glass) are clear, vertical movement of plastics appears to be more complicated. Understanding vertical transport of plastic will require an understanding of biophysical and chemical processes that contribute to its breakdown and affect its buoyancy (Hollstrom, 1975; Ye and Andrady, 1991). Many, but not all, plastics are neutral to positively buoyant and thus remain on or near the ocean surface. Nylons, aramids, and many carbon fiber compounds used as high-tensile cording are neutral to negatively buoyant and sink to the benthos. Moreover, through photodegradation, mechanical breakdown, or fouling with organic matter, even buoyant plastic debris sinks or is transported to the benthos. However, the long-term fate of marine debris on the benthos is unclear as erstwhile buoyant debris has been observed to become unfouled and return to the surface (Ye and Andrady, 1991). Given the difficulty of sampling the seabed, understanding both the dynamics of the vertical transport of plastics as well as the degradation of plastics at different depths would be useful in understanding the full extent of the marine debris problem in the oceans. IMPACTS Understanding the impacts of different types of marine debris is as important as understanding its temporal and spatial prevalence. Not all types of debris are equally harmful, and not all organisms or regions are equally vulnerable. To prudently use scarce or limited resources in mitigation efforts, it is important to fully understand the impacts of marine debris on the environment and on human uses. Horrific images of seabirds, turtles, and marine mammals, dead and dying as a result of ingesting or becoming entangled in debris, have often been the public image of the marine debris problem. This section illustrates the serious consequences of marine debris in the environment, beginning with the ecological implications and concluding with a discussion of some of the socioeconomic impacts. Although understanding of the full breadth of impacts is far from complete, it is nonetheless clear that enough is known to warrant action.
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Tackling Marine Debris in the 21st Century Ingestion Ingested marine debris, particularly plastics, has been reported in necropsies of birds, turtles, marine mammals, fish, and squid (Laist, 1997). A review of the literature1 indicates that ingested marine debris is quite common in samples of dead and captured seabirds and turtles (see Appendix C, Table IV). The large variation in the prevalence of ingested debris does not appear to correlate with any particular taxa, region, or time period. However, there may be regional trends. For example, Robards et al. (1995) reported that the number of plastic particles ingested by some seabird species has increased over time in the subarctic waters off of Alaska. The known effects of ingestion of marine debris by birds include reducing the absorption of nutrients in the gut, reducing the amount of space for food in the gizzard and stomach, uptake of toxic substances that comprise the debris or have been adsorbed onto the debris, ulceration of tissues, and mechanical blockage of digestive processes (Azzarello and Van Vleet, 1987; Fry et al., 1987; Ryan and Jackson, 1987; Ryan, 1988; Spear et al., 1995; see also Table IV in Appendix C). Prevalence of debris ingestion among seabirds is suggestive of a broad and significant ecological impact, at least in some regions such as the North Pacific Ocean. However, a direct link between ingestion and mortality has been limited to incidental examinations of a small number of birds (Pierce et al., 2004). Spear et al. (1995) found a statistically significant positive correlation between body weight and the presence of plastic particles and a statistically significant negative correlation between the number of plastic particles ingested and body weight. Other studies have failed to detect a statistically significant correlation between plastic ingestion and body condition (Furness, 1985; Sileo et al., 1990; Moser and Lee, 1992; Shaw and Day, 1994; Vlietstra and Parga, 2002). In addition to the possible direct physical effects of marine debris, there is concern that plastics, particularly microplastics, are able to adsorb, concentrate, and deliver toxic compounds to organisms that ingest them or to benthic communities. Microplastics are the very small (approximately ≤5 mm) plastic debris items; sources include preproduction plastic resin pellets used in the manufacture of plastic items (Gregory, 1977, 1978; Shiber, 1979, 1982, 1987; Redford et al., 1997; Moore et al., 2001b), tiny bead “scrubbers” used in washing products (Zitko and Hanlon, 1991; Gregory, 1996), abrasive plastic beads used to clean ships (Reddy et al., 2006), and ever-smaller fragments resulting from the mechanical and photodegra- 1 Only publications citing samples sizes greater than 20 individuals examined were included in this review. The literature includes many additional reports of ingestion by seabirds, turtles, marine mammals, and fish, but these are generally limited observations that are not suitable for estimating population-level frequencies.
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Tackling Marine Debris in the 21st Century dation (oxidation) of larger plastic debris (Andrady, 1990; George, 1995). Plastic resin pellets have been shown to adsorb hydrophobic organic contaminants including polychlorinated biphenyls (PCBs), dichlorodiphenyl-dichloroethylene (DDE), and nonylphenols (Mato et al., 2001; Endo et al., 2005; Rios et al., 2007). Mato et al. (2001) suggested that contaminated plastic particles may serve as a source of toxins to organisms that ingest them. Teuten et al. (2007) showed that sorption of contaminants to plastics greatly exceeded that to two natural sediments, and that as little as 1 μg of polyethylene contaminated with phenanthrene per gram of sediment significantly increased the accumulation of this contaminant by an invertebrate worm; they postulated that plastic may serve to transport hydrophobic contaminants to sediment-dwelling organisms at the base of the food chain and as such provide a mechanism for amplification of contaminants throughout the food web (e.g., Gregory, 1996). The small size of microplastic marine debris allows it to be ingested by a wide range of organisms. Microplastic particles as small as 20 μm can be ingested by invertebrates, including lugworms, barnacles, and amphipods (Thompson et al., 2004), and by protochordates such as salps (Moore et al., 2001a). The ingestion of plastic particles by seabirds and marine mammals has also been widely reported (Fry et al., 1987; Moser and Lee, 1992; Laist, 1997; Robards et al., 1997). Moreover, the correlation between toxic load and amount of plastic ingestion in seabirds has been known for two decades (Ryan et al., 1988). Toxic effects would be expected to compound damage resulting from the suite of known impacts related to the ingestion of plastics by marine birds. Although the effects of plastic ingestion may not currently rise to the level of significantly impacting population-scale dynamics, ingestion of plastic debris may impede the recovery of species listed under the Endangered Species Act (16 U.S.C. § 1531 et seq.). Furthermore, ingestion-related injuries and mortalities, even those that do not threaten populations, may evoke substantial public concern. Entanglement The effect on organisms of entanglement in marine debris ranges from restricting the movement of affected individuals to direct physical harm and mortality. Sessile animals are not immune from what could be considered a form of entanglement via the scouring, abrading, or breakage they experience, as in the case of live coral reefs, when marine debris snags or entangles them (as discussed later under “Other Ecological Impacts”). Although entanglement morbidity and mortality of individual animals is of concern, the potential effect of entanglement on animal populations is also of conservation and legal interest.
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Tackling Marine Debris in the 21st Century Three pieces of information are needed to understand the population-scale impacts of entanglement: entanglement rate, entanglement-related mortality rate, and the demographic structure of the species or population under study. Of the many studies reporting on debris entanglement, few provide entanglement rates, fewer provide mortality rates, and only a handful report mortality rates in the context of populations (see Appendix C, Table V). Most quantitative studies of debris-related entanglements have focused on marine mammals, birds, and turtles (see Appendix C, Table V). The prevalence of entanglement (number of cases per population) was generally less than 1 percent; however, entangled animals may die unobserved at sea or otherwise fail to return to land after entanglement, confounding both entanglement rates and subsequent fate of entangled animals (Laist, 1997). Entanglements typically involve debris that encircles the neck or appendages, most commonly plastic packing straps, followed by rope and line, and net fragments (Laist, 1997; Henderson, 2001). Once entangled, mortality rates differ among species from more than 80 percent for Antarctic fur seals, 44 percent for Australian sea lions, and 57 percent for entangled New Zealand fur seals (Croxall et al., 1990; Page et al., 2004). Entanglement of the most endangered seal in the United States, the Hawaiian monk seal, is arguably the most significant documented impediment to the species’ recovery (Boland and Donohue, 2003), with a mean annual population entanglement rate of 0.70 percent reported from 1982 to 1998 (Henderson, 2001). In addition to entanglement rates and entanglement-induced mortality rates, whether entanglement poses a significant threat to a species or stock is dependent on the demographic structure of the species or population (e.g., population growth rates). For instance, Fowler (1987) suggested that even though the entanglement rate for northern fur seals in the Pribilof Islands, Alaska, was less than 0.5 percent, an estimated entanglement-related mortality rate among juveniles of 15 percent is thought to have contributed to the decline in this species, which is now listed as depleted under the Marine Mammal Protection Act of 1972 (16 U.S.C. § 1361 et seq.). An additional example is the critically endangered Hawaiian monk seal. With 1,250 individuals remaining (Carretta et al., 2007), the success of juvenile recruitment is key to the species’ survival. Juvenile Hawaiian monk seals have been shown to become entangled more frequently than adults (Henderson, 2001), hampering the species’ recovery. For other species reviewed here, entanglement has not been found to be an important factor in the current status of their populations (Croxall et al., 1990; Arnould and Croxall, 1995; Zavala-González and Mellink, 1997; Hanni and Pyle, 2000; Hofmeyr and Bester, 2002; Hofmeyr et al., 2006).
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Tackling Marine Debris in the 21st Century As with debris ingestion, even if entanglement-induced mortality does not rise to a level that significantly impacts population viability, entanglement may impede the recovery of species listed under the Endangered Species Act and may evoke substantial public concern. There is no clear temporal trend in entanglement rates among marine mammals as a group (see Appendix C, Table V). While some studies have documented declines in entanglement rates that may be attributed to implementation of MARPOL Annex V (e.g., Antarctic fur seal as reported by Arnould and Croxall ), others have reported increased entanglement rates (Zavala-González and Mellink, 1997; Page et al., 2004). The one study specifically evaluating the impact of MARPOL Annex V found no post-implementation abatement of entanglement of the endangered Hawaiian monk seal (Henderson, 2001). Moreover, separating the effect of MARPOL Annex V from the background of other regulatory and institutional changes can be problematic. For example, reported changes in northern fur seal entanglement rates (e.g., Fowler and Baba, 1991) did not account for the effects of radical changes in the structure and organization of the Bering Sea fisheries that took place during the 1980s and 1990s that may have been the ultimate cause of the variations observed in northern fur seal entanglements. Ghost Fishing Ghost fishing is a widely acknowledged but poorly understood problem of derelict fishing gear (DFG). To fully comprehend the magnitude of the impact, a number of parameters must be determined, including the amount of lost gear, catch or mortality rates, the length of time the gear continues to actively fish, and the dynamics and demographics of the populations of fish and shellfish captured in the gear (Breen, 1987). Because these parameters vary by fishery and even by location for a given fishery, the biological and economic impacts of ghost fishing are difficult to quantify. Additional discussion of the characteristics of fishing gear types, causes of gear loss, and impacts is included in Chapter 4. Ghost fishing is primarily a problem associated with static gear such as gillnets, hook-and-line, traps, cages, and pots rather than active gear such as seines and trawls. Studies show that gillnets, once lost, can continue to actively fish for some time (see Appendix C, Table VI). While ghost nets can cause substantial mortality, estimates suggest that ghost fishing mortality in gillnets and tangle nets is a small fraction of directed catches. For example, Sancho et al. (2003) and Brown and Macfayden (2007) estimated that ghost fishing losses do not exceed 5 percent of commercial landings in European gillnet and tangle net fisheries. However, in the case of small stocks, ghost fishing mortality may be a cause
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Tackling Marine Debris in the 21st Century for conservation concern. For example, Kappenman and Parker (2007) reported that ghost gillnets may continue to be active for as long as 7 years and are estimated to account for annual losses of 545 white sturgeon (Acipenser transmontanus) in the Columbia River, a mortality rate that is approximately one-third the magnitude of the commercial harvest. As nets become fouled (i.e., become more visible) or collapse due to initial capture, ghost fishing capacity declines. In contrast, for traps, cages, and pots, which are used to target crustaceans and some species of finfish, ghost fishing can persist for as long as the gear remains intact. Thus, a key component of understanding the impact of derelict traps is to determine mortality rates within the traps. As indicated in Appendix C, Table VII, these mortality rates range from 7 to 100 percent. For example, in the case of the Dungeness crab fisheries in the Fraser River Estuary, British Columbia, Breen (1987) estimated that derelict crab pots are responsible for approximately 7 percent of the total catch. The rate of trap loss is also an important factor. Estimates for annual trap loss in the Gulf of Mexico blue crab fishery range from 20 to 100 percent, with higher losses after hurricanes or other severe storms (Guillory et al., 2001). In the Alaskan crab fisheries, during the 1980s, pot losses are thought to have been on the order of 20,000 per year and, even with fewer pots under current limits, pot losses are thought to be about 5,000 per year (Stevens et al., 2000). Although most U.S. trap, cage, and pot fisheries require that pots be equipped with rot cord—sections of twine that compromise the integrity of the pot once they biodegrade—Barnard (2008) determined that the mean failure rate for 30-thread cotton twine is 77–89 days; thus, even properly equipped traps could continue to ghost fish for an extended period. Stevens et al. (2000) reported that one rot cord–equipped ghost pot off Kodiak, Alaska, held 125 crabs. Moreover, there is some anecdotal evidence that compliance with rot cord requirements is incomplete, and that encrusting organisms, such as anemones, can overgrow escape doors and can keep doors functionally closed for years. Derelict pots can also get turned in a way that prevents proper functioning of the escape panels. Ghost fishing losses to hook-and-line gear are poorly documented, but could be substantial for longline gear (National Research Council, 1999). Other Ecological Impacts Several studies have suggested that marine debris can act as a transport and dispersal vector for a range of encrusting or clinging species (Winston et al., 1997; Barnes, 2002; Lewis et al., 2005). In a study that confirms this possibility, Zabin et al. (2004) documented the presence of a nonnative sea anemone transported to NWHI on DFG.
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Tackling Marine Debris in the 21st Century Marine debris may also act as an “ecological trap,” which affects spatial distributions and migratory patterns or makes large segments of the pelagic community vulnerable to capture. A recent study found that tuna associated with artificial fish aggregating devices (FADs) are less healthy than unassociated tuna (Hallier and Gaertner, 2008). Derelict FADs and other debris assemblages that routinely form along convergence zones or fronts (Pichel et al., 2007) may act as ecological traps by eliciting habitat selection behaviors that are not associated with feeding benefits. Schlaepfer et al. (2002) suggested that the ecological trap effect could be particularly severe when the affected population size is already small (see Chapter 4 for further discussion). Another impact of marine debris is damage to coral reefs and other benthic communities through entanglement and abrasion. The extent of the damage is dependent on the nature (i.e., size, prevalence, composition) of the debris and the fragility and resilience of the affected environment. In NWHI, Donohue et al. (2001) showed that DFG was responsible for damage to benthic coral reef habitat. Given the continual input of DFG into upcurrent areas (Boland et al., 2006; Dameron et al., 2007), marine debris poses a significant and persistent threat for the reefs of NWHI. In the Florida Keys National Marine Sanctuary, Chiappone et al. (2005) found that hook-and-line fishing gear was the most common type of debris on the reef but noted that the biological impacts were minor, adversely affecting 0.2 percent of the species present. Socioeconomic Impacts Marine debris can also reduce direct and indirect socioeconomic benefits (use values, option values, and nonuse values) or increase direct or indirect costs (National Research Council, 2004). Direct benefits include the value of commercial, sport, subsistence, and other cultural harvests; marine transportation; and the benefits that beachgoers, boaters, and divers derive from recreating at the seashore and on marine waters (Smith and Palmquist, 1994; Kaoru et al., 1995; Kirkley and McConnell, 1997; Smith et al., 1997). The following are ways in which marine debris can reduce direct socioeconomic benefits: sustainable harvests or catch-per-unit-effort of valued fish and shellfish due to ghost fishing (Kirkley and McConnell, 1997; National Research Council, 1999); actual and contingent benefits of coastal recreation due to the presence of litter and other marine debris, including hazardous materials that present human health dangers; and net benefits for commercial and recreational boaters from fouling of
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Tackling Marine Debris in the 21st Century propellers and jet intakes as well as damage to hulls (Kirkley and McConnell, 1997). In addition to direct losses in economic well-being, marine debris can contribute to adverse local economic impacts when beachgoers forego trips to impaired beaches in favor of other recreation opportunities. Ofiara and Brown (1999) and Swanson et al. (1991) estimated that New Jersey lost between $379 million and $3.6 billion in tourism and other revenue as a result of debris washing ashore in 1988. In a South African study, Ballance et al. (2000) estimated that “more than 10 large items per meter of beach would deter 40 percent of foreign tourists, and 60 percent of domestic tourists interviewed, from returning to Cape Town. The impact of this on the regional economy could be a loss of billions of rands each year.” An example of the costs of marine debris removal is presented in an analysis of DFG removal activities by Natural Resources Consultants, Inc. (2007): Costs of derelict net survey and removal totaled $4,960 per acre of net removed. Costs of survey and removal of derelict pots/traps totaled $193 per pot/trap. Directly measurable monetized benefits of derelict fishing gear removal were based on the commercial ex-vessel value of species saved from mortality over a one-year period for derelict pots/traps, totaling $248 per pot/trap and a ten-year period for derelict nets, totaling $6,285 per net. Option benefits reflect the value that individuals derive from reserving the opportunity to engage in coastal recreation or to benefit from coastal amenity services, such as viewing wildlife, at some future time (Bishop, 1982; Freeman, 1984). Awareness of a growing marine debris problem could reduce option value by reducing the probability that individuals will travel to the seashore to recreate or by reducing the benefit they expect to derive from future beach recreation. Nonuse or vicarious benefits are those obtained from knowledge of the existence of desirable coastal environments, the value derived from being able to bequest unimpaired resources to future generations, the altruistic benefits of preserving attractive coastal resources for other users, and the value associated with the belief that maintaining a litter-free coast and ocean is intrinsically desirable (Brown and Goldstein, 1984; Walsh et al., 1984). Socioeconomic studies not only help define impacts, but they also can assist with mitigation by improving the understanding of the actions that lead to debris generation. Human behavior is the ultimate cause of marine debris, and the factors that lead to marine debris generation must
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Tackling Marine Debris in the 21st Century ultimately be understood and addressed to achieve prevention. At least one study has addressed some of the social aspects of marine debris. Santos et al. (2005b) explored the generation of marine debris on beaches in Brazil and found that tourism was the main source of marine debris; debris levels were correlated with visitor density, and daily litter input to the beach was significantly higher in the regions frequented by people with lower annual income and literacy. Further studies elucidating the role of education level in environmental awareness and human behavior relative to marine debris generation will be needed to ensure a successful long-term solution. Finding: Despite measures to prevent and reduce marine debris, evidence shows that the problem continues and will likely get worse. This indicates that current measures for preventing and reducing marine debris are inadequate. Recommendation: Both the United States and the international maritime community should adopt a new approach to prevent and reduce marine debris with more rigorous measures based on a goal of zero discharge of waste into the marine environment. Finding: While a great deal has been learned about marine debris, there are still many gaps in the understanding of marine debris sources, abundance, fates, and impacts. These gaps in knowledge hinder the ability to prioritize mitigation efforts and to assess the effectiveness of measures that have been implemented. Recommendation: Additional studies are needed to assess the effectiveness of measures to prevent and reduce marine debris and to provide useful guidance to managers and decision makers for debris mitigation. In particular, the Interagency Marine Debris Coordinating Committee (IMDCC) should sponsor and facilitate research in the following areas: Abundance and fluxes: Additional longitudinal marine debris monitoring surveys are needed, particularly for benthic and pelagic debris and for debris fluxes, to identify regional differences and trends in the prevalence, distribution, makeup, and fate of debris. Surveys should pay attention to microplastics as well as macro debris. Survey designs should allow for and encourage comparisons of obtained data. Ecological impacts: Future studies on ecological impacts should be designed to provide quantitative estimates of the impact of marine
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Tackling Marine Debris in the 21st Century debris on affected populations and ecosystems and, in addition, have a broad taxonomic focus. Socioeconomic impacts: Additional studies should be conducted on the socioeconomics of marine debris, particularly in surveys that explore the human social and behavioral aspects of marine debris generation. If these studies are to be useful for management, it will be crucial that they be designed in a rigorous manner. Long-term monitoring that allows for comparison of data and evaluative metrics is also important. The elements of a well-designed marine debris survey program are described in the next section. EFFECTIVE MONITORING AND RESEARCH The committee’s review of the record of marine debris monitoring and research activities found few studies, with some noted exceptions (e.g., Ryan and Moloney, 1993; Henderson, 2001; Barnes, 2005; Sheavly, 2007), that were useful as a reliable indicator of change in marine debris in response to regulatory or other mitigating activities. A large number of studies have been conducted that document aspects of the marine debris problem and the many efforts to manage it, but these are mostly descriptive, anecdotal, and temporal. As discussed in the previous sections, the available body of information documents the complexity of the marine debris problem but does not reliably track the changes in those problems over time and provides little functional insight into the factors controlling and contributing to the marine debris problem. Many studies that purportedly address the effectiveness of MARPOL Annex V address it a posteriori and are unable to link changes in debris definitively to regulatory actions versus other factors. To effectively address marine debris, its scope, sources, causes, and effects, as well as spatial and temporal variability, need to be understood. Mechanisms for objective evaluation must be available to judge the environmental, economic, social, and cultural efficacy of management and mitigation measures. There is a lack of metrics for evaluating the effectiveness of measures implemented to prevent and reduce marine debris, including the effectiveness of specific regulatory and management actions (e.g., education, enforcement actions). Scientifically rigorous monitoring, assessment, and evaluation programs are necessary to understand and address the problem. Definitions of monitoring, assessment, and evaluation can vary; however, the committee treats them as research activities and advocates conducting them within a structure of systematic, rigorous information collection. In exploring monitoring and research, the importance of
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Tackling Marine Debris in the 21st Century research planning and prioritization and the considerations in designing rigorous monitoring and assessment programs, including emerging issues and technologies, are discussed. Research Planning and Prioritization Research planning and prioritization need to be driven by a national strategic plan that identifies objectives related to the prevention, mitigation, and remediation of marine debris while remaining nimble enough to address novel issues as they emerge. As described earlier, more research and monitoring are needed to better understand the nature, prevalence, and impacts of marine debris, as well as the effectiveness of measures to address the marine debris problem. Strategic planning and prioritization could also assist in identifying opportunities for incorporating additional technologies or collaborating with other disciplines to maximize the value of marine debris research, given limited resources. Researchers could take better advantage of technologies such as remote sensing and Internet data management and sharing. Data and information gathered from marine debris monitoring, assessment, and research activities could also be incorporated into the emerging national and international efforts to develop an Integrated Ocean Observing System. There are also opportunities for researchers to add onto existing research programs, particularly other longitudinal oceanographic monitoring efforts. Research into the distribution and prevalence of microplastics may be particularly well suited for piggybacking onto existing research programs. Microplastic marine debris has been, and could continue to be, effectively surveyed during ongoing longitudinal plankton surveys run by California Cooperative Oceanic Fisheries Investigations (CalCOFI), the Ecosystems and Fisheries–Oceanography Coordinated Investigations (EcoFOCI), and others. Similarly, sampling of microplastics and other marine debris could be included through additional instrumentation as part of buoys deployed under the Integrated Ocean Observing System. This type of leveraging will add value to and help ensure the long-term sustainability of longitudinal oceanographic monitoring programs. Finding: A diversity of research on marine debris is conducted, some of it funded by the U.S. federal government, primarily NOAA. However, there is no overall needs assessment available to guide this research. As a result, research completed is rarely integrated at the regional, national, international, or even local levels. Therefore, there is little opportunity for expanding the understanding of marine debris by fitting these individual research activities into a congruous whole.
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Tackling Marine Debris in the 21st Century Recommendation: An information needs assessment should be conducted at the national level by IMDCC with input from stakeholders. A detailed national marine debris research priorities plan should be developed from the results. This research plan should direct future federal funding of a suite of marine debris studies that, when taken together, will provide a comprehensive characterization of the marine debris problem. Such research can serve to inform policy and mitigation actions. Design of Monitoring, Assessment, and Evaluation Programs Effective monitoring, assessment, and evaluation programs are also crucial to providing useful information to assess and improve measures to prevent and reduce marine debris. Thoughtful and scholarly analysis of marine debris monitoring, assessment, and evaluation efforts have been completed and many aspects of these works remain relevant (e.g., Ribic, 1990; Ribic et al., 1992). The use of this substantive body of work applied with the benefit of rapidly emerging technologies and advanced analytical methods to current conditions is urgently needed. These efforts must also meet the needs of those seeking to both prevent and mitigate the impacts of marine debris and those needs must be clearly identified. The characteristics of robust monitoring, assessment, and evaluation activities are relatively straightforward in composition and have been promoted and revisited repeatedly (e.g., Ribic et al., 1992; Lovett et al., 2007). While marine debris presents in a myriad of forms and sizes, standard experimental design principles are applicable and should be employed routinely in future surveys. As described earlier, NMDMP is an example of a well-designed and scientifically rigorous program for monitoring changes in the composition and prevalence of shoreline marine debris on U.S. coasts. Because a standard sampling protocol was maintained through time and across regions and because sample sites were drawn from a stratified random sample of coast sections, data generated by NMDMP are suitable for a scientifically valid analysis of trends in debris prevalence, across regions and through time. In addition, the data include information on specific indicator items that may be suitable for assessing the effectiveness of targeted source reduction programs. However, the NMDMP survey was conceived as a five-year program and was completed in 2006; there are currently no other ongoing, long-term monitoring programs of this nature. Moreover, NMDMP was designed to provide information about general regional trends and may not be suitable for fine-scale assessments of local trends in deposition or influx from waterways and storm drains.
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Tackling Marine Debris in the 21st Century The United Nations Environment Programme is currently engaged in a global initiative on marine litter with plans to develop targeted regional activities to monitor marine debris, among other activities. This initiative has noted the importance of standardizing monitoring protocols to allow for regional comparisons; it plans to develop “substantive guidelines and recommended policies on harmonizing monitoring systems of marine litter” (United Nations Environment Programme, 2008). This initiative provides an opportunity for the United States and other nations to coordinate their monitoring efforts to ensure comparability. Finding: Well-designed and statistically rigorous longitudinal marine debris monitoring programs are needed at a variety of spatial and temporal scales. However, standardization of protocols is necessary to ensure that the results of various surveys are comparable. Recommendation: Long-term marine debris monitoring programs should be established by IMDCC (for the United States) and appropriate international organizations such as the United Nations Environment Programme (for global monitoring). These programs should allow for statistically valid analysis of marine debris quantities and trends as a metric of the effectiveness of measures to prevent and reduce marine debris. To the extent practical, these programs should adopt a suite of common design characteristics and protocols to facilitate cross comparisons and meta-analyses. Remote sensing using satellites, planes, remotely operated vehicles, and other devices represents a promising technology for assessing the nature and extent of marine debris and enhancing understanding and mitigation because of its ability to systematically observe and measure large or otherwise inaccessible areas of the ocean. For example, airborne synthetic aperture radar is a type of remote sensing instrument that has the potential to identify, map, and guide the removal of plastic debris at sea at very fine scales, particularly for large debris items such as DFG. While synthetic aperture radar is a fairly new technology and not readily available, there are also a variety of similar existing tools available to researchers (e.g., remote sensing instruments mounted on U.S. Coast Guard aircraft) that could be used in studies and efforts to mitigate marine debris. Remote sensing, in combination with ocean circulation models, shows particular promise in identifying areas of debris accumulation in the open ocean for targeted remediation efforts (Kubota, 1994; Ingraham and Ebbesmeyer, 2001; Polovina et al., 2001; Bograd et al., 2004; Kubota et al., 2005; Pichel et al., 2007). An example of a public–private partnership that is using remote sensing data from both satellites and aerial surveys
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Tackling Marine Debris in the 21st Century to mitigate marine debris is the “GhostNet Project” (Airborne Technologies Incorporated, Wasilla, Alaska), which successfully located over 2,000 debris items in the open ocean (Pichel et al., 2007). Using remote sensing data for mitigation can be challenging given the difficulty in verifying marine debris locations with sufficient precision and within acceptable timeframes and costs to direct removal efforts (e.g., ship-based recovery of marine debris), particularly given the mobile nature of floating marine debris. Although the recovery of marine debris via dedicated ships can be costly (e.g., Donohue  reported $30,000 per ton), targeting these efforts by identifying high-density debris areas using remote sensing could significantly minimize operational costs. Remote sensing has also proven helpful in understanding marine debris impacts. For example, remote sensing has been used to detect phytoplankton blooms caused by floating plastic, which provides an artificial substratum (Mato et al., 2001; Barnes, 2002). Morishige et al. (2007) used remote sensing to show that marine debris deposition in NWHI is influenced by the El Niño/La Niña phenomenon, while Donohue and Foley (2007) used remote sensing to show that Hawaiian monk seal entanglement is greater in El Niño years. Marine Debris Information Clearinghouse There is a significant opportunity with regard to the dynamic use of the Internet and other emerging technologies for practitioners whose actions may directly influence marine debris generation and mitigation. The marine debris “clearinghouse,” as called for in the recent U.S. Marine Debris Research, Prevention, and Reduction Act (33 U.S.C. § 1951 et seq.), has the potential to contribute to this purpose if crafted with consideration of the multiple users that influence marine debris sources and solutions. Data management is an important component of such a clearinghouse site both to make marine debris data widely available and to promote standardized marine debris data collection protocols. There are many good examples of protocols for establishing a data archive meta-database system and for providing ready access. The Marine Conservation Alliance Foundation’s Google™ map interface (Marine Conservation Alliance Foundation, 2008) is an example of a user-friendly way to layer information on the distribution of debris and the conduct of cleanup activities. Finding: The value of data stored in the marine debris information clearinghouse, mandated by the Marine Debris Research, Prevention, and Reduction Act, will depend on how well it is standardized, how well it is integrated into a meta-database, and whether it is readily accessible to researchers and the public.
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Tackling Marine Debris in the 21st Century Recommendation: The marine debris information clearinghouse should be given high priority. It should be housed and maintained by NOAA but available to the public and researchers at large. Data generated by federally funded research should be submitted to this clearinghouse in a timely manner. CONCLUSION The following finding and recommendation express overarching concepts discussed in the previous findings and recommendations in Chapter 2. Overarching Finding: Although there is clear evidence that marine debris is a problem, there has not been a coordinated or targeted effort to thoroughly document and understand its sources, fates, and impacts. This confounds the ability to prioritize mitigation efforts and to assess the effectiveness of measures that have been implemented. Overarching Recommendation: IMDCC should, through planning and prioritization, target research to understand the sources, fates, and impacts of marine debris. It should support the establishment of scalable and statistically rigorous protocols that allow monitoring at a variety of temporal and spatial scales. These protocols should contain evaluative metrics that allow an assessment of progress in marine debris mitigation. The United States, through leadership in the international arena, should provide technical assistance and support for the establishment of additional monitoring and research programs worldwide.
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