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APPENDIX F 335 Based on anecdotal reports, monofilament fishing line may be the item most often known to entangle birds. During the 1991 and 1992 International Coastal Cleanups coordinated by the Center for Marine Conservation (CMC), 56 of the 120 reported cases of bird entanglements involved fishing lines (Younger and Hodge, 1992; Hodge et al., 1993). It should be noted that these animals were reported on just a fraction of the U.S. coastline within a few hours. Hence, it would seem worthwhile to investigate just how serious a problem monofilament line poses to birds. In some cases, birds may become entangled in fishing lines when they attempt to eat bait from fishing hooks. An entangled bird trailing line either may be immobilized immediately or may become snagged on a tree or power line, unable to break free. Other items, such as plastic six-pack rings, get stuck around the necks of marine birds and waterfowl when they attempt to dive or feed through the rings. Ospreys, cormorants, and other birds actively collect pieces of nets and fishing line for nest material; this activity can lead to strangulation of both adults and their young (O'Hara and Iudicello, 1987; Podolsky and Kress, 1990). Little is known about the extent of entanglement among species of cetaceans. The lack of knowledge may be due to the fact that these animals are only found on occasions when they wash ashore, added to the expense of and sometimes lack of expertise for conducting necropsies. Information on the entanglement of fish in marine debris is largely anecdotal at present. During the 1992 International Coastal Cleanup, volunteers reported approximately 20 cases of entanglement of fish and crustaceans in debris in just three hours. The range of items found to ensnare fish is remarkable. The CMC maintains a photograph library of wildlife interactions with debris that includes pictures of a gar and bluefish in plastic six-pack rings, sharks in plastic straps and cables, a red drum in a plastic vegetable sack, and a bill fish with a plastic baby bottle cap on its bill. Finally, there have been sporadic accounts of debris on coastlines entangling terrestrial species, For example, foxes and rabbits have been observed entangled in nets and other plastic items (Fowler and Merrell, 1986; O'Hara and Younger, 1990). In one case, the skeletal remains of 15 reindeer were found in Ã¡ Japanese gill net on a beach in Alaska (Beach et al., 1976). But again, this information is not compiled by any agency. INGESTION OF PLASTICS BY MARINE SPECIES Along with increasing reports of wildlife entanglement involving plastic debris, there has been growing documentation of a less obvious problem: the ingestion of plastics by marine species. There appears to be some understanding of the factors that may increase the likelihood of plastic ingestion by certain species. For example, winds and currents that tend to concentrate food sources such as fish and plankton also concentrate debris. For some species, floating
APPENDIX F 336 items actually may resemble authentic food items. Seabirds, for example, are thought to mistake small pieces and fragments of plastic for planktonic organisms, fish eggs, or even the eyes of squid or fish (Day et al., 1985). Plastics covered with fish eggs or encrusting organisms such as barnacles, algae, and bryozoa may even "smell" or "taste" like authentic food. It has been suggested that hungry animals are less likely than are satiated animals to discriminate between natural foods and look-alike debris and are more likely to eat the plastic items (Balazs, 1985). Perhaps the most highly publicized example of plastic ingestion has been the consumption of plastic bags or sheeting by sea turtles that are thought to mistake these items for jellyfish, squid, and other prey. In the only comprehensive review of this subject, Balazs (1985) reported five species of sea turtles known to ingest plastics: green, loggerhead, leatherback, hawksbill, and Kemp's ridley. Of the items ingested, plastic bags and sheets were most common (32 percent of 79 cases) followed by tar balls (20.8 percent) and plastic particles (18.9 percent). On San Jose Island, Texas, Amos (1993) reported that 20 to 30 percent of plastic containers that wash ashore exhibit bite marks from turtles. Plotkin and Amos (1990) reported ingestion of plastic and other man-made debris by 46 percent of 76 sea turtles stranded on Texas beaches in an 18-month period. Items found in turtle guts included plastic bags, foamed plastic "peanuts," balloons, strapping band fragments, polypropylene rope, as well as miscellaneous plastic pieces. In some cases, the stomach and gut were completely impacted with plastic. The angular shapes and the rigidity of some of the plastic pieces are not dissimilar to fragments of natural prey that must be excreted, such as crustacean carapaces and sea-pen stalks. Recent studies suggest that young turtles that congregate to feed in the open ocean at areas of convergence are particularly prone to ingesting plastics. The downwelling in these areas concentrates not only turtle food but also plastic debris. For all turtles species, with the exception of the leatherback (which is rarely seen in immature stages), reports of immature animals that have ingested debris are more common than are reports of adults (Balazs, 1985). Cart (1987) noted that plastic pellets found in the stomachs of dead juvenile sea turtles are similar in size and shape to sargassum weed, which concentrates in areas of convergence and provides both shelter and sources of food for turtles. The effect of plastics ingestion on sea turtle longevity and reproductive potential is unknown. It is thought that ingested plastics may cause mechanical blockage of the digestive tract, starvation, reduced absorption of nutrients, and ulceration. Buoyancy caused by plastics also could inhibit diving activities needed for pursuit of prey and escape from predators (Balazs, 1985). For several reasonsâthe prevalence of plastic ingestion among sea turtles, the significant lesions and mortality caused by ingested items, and the fact that all species of sea turtles are threatened with extinctionâthe effects of ingestion of debris on sea turtles is considered a research priority (Sileo, 1990).
APPENDIX F 337 The ingestion of plastic debris by seabirds also has received attention in recent years. The first documented report of plastic ingestion by a seabird, a Layson albatross, was in the 1960s (Kenyon and Kridler, 1969). Today, at least 80 of the world's 280 seabird species are known to ingest plastic debris (Harrison, 1983). This tendency appears to be closely related to bird feeding habits, with diving birds having the highest incidence of plastic ingestion. Most bird species also exhibit preferences for certain types of plastic based on debris color, shape, or size. For example, the parakeet auklet, which feeds primarily on planktonic crustaceans, was found to ingest large amounts of light-brown plastic particles that are similar in size and shape to its crustacean prey. Some birds also feed plastics to their young. In one study, all of the 300 Layson albatross chicks examined on Midway Islands of Hawaii (located more than 1,600 km [1,000 miles] northwest of the nearest populated Hawaiian islands) had ingested plastic debris, including plastic fragments, toys, bottle caps, balloons, condoms, and cigarette lighters (Sileo et al., 1990). Although many birds naturally digest and regurgitate hard, nonfood items such as: fish bones and bottom substrate, some researchers believe that large quantities of ingested plastics may cause intestinal blockage or a false feeling of satiation or may reduce absorption of nutrients, thus robbing the animal of needed nutrition (Day et al., 1985). Suffocation, ulceration, or intestinal injury could be caused by jagged edges on plastics or grinding of these items against intestinal walls. Long-term effects Of plastics ingestion may include physical deterioration due to malnutrition, decreased reproductive performance, and the inability to maintain energy requirements (Day et al., 1985). Limited data are available concerning ingestion of plastic debris by marine mammals, although information from marine parks and zoos suggests that debris ingestion has the potential to be a direct cause of mortality (Walker and Coe, 1990). Several species of wild cetaceans have been found to ingest plastics, primarily in the form of bags and sheeting (Martin and Clarke, 1986; Barros et al., 1990; Walker and Coe, 1990). Because most of this information was obtained through studies of dead animals that had stranded, the actual cause of death is uncertain. In Texas, however, a stranded pygmy sperm whale, which was taken into captivity, died later from the effects of plastic garbage bags, a bread wrapper, and a corn chip bag ingested while in the wild (O'Hara et al., 1987). Analyses of the stomach contents of sperm whales at an Icelandic whaling station from 1977 to 1981 revealed plastic drinking cups and children's toys as well as large pieces of fishing nets. Because sperm whales readily ingest and subsequently regurgitate the hard parts of prey, principally fish bones and cephalopod beaks, small pieces of plastic are thought to pose no significant problem. But in one case, an ingested fishing net weighing 139 pounds was considered to be large enough to cause eventual starvation of the sperm whale. Other marine mammals that have died as a result of ingestion of debris include a northern elephant seal and a Steller sea lion (Mate, 1985). Walker and