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SOURCES, FATES, AND EFFECTS OF SHIPBORNE GARBAGE 55 extent of entanglement among cetaceans, perhaps because these animals are found only on occasions when they wash ashore, and necropsies are done only when adequate expertise and funding are available. Entanglements have been reported for 10 (13 percent) of the 75 cetacean species (Laist, 1994). Information on the entanglement of fish in marine debris is also largely anecdotal. Ingestion of Plastics by Marine Species The most highly publicized example of plastic ingestion may be the consumption of plastic bags or sheeting by sea turtles, which are thought to mistake these items for jellyfish, squid, and other prey. Turtles, especially hawksbills, also eat encrusting organisms that grow on floating plastic and ingest plastic pieces as a ''by-product'' (Plotkin and Amos, 1988). 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; Lutz, 1990). Birds and fish also ingest plastics. At least 108 of the world's 312 seabird species are known to ingest plastic debris (Laist, 1994). Individuals from 33 fish species have been reported to ingest plastics (Laist, 1994); a list compiled by Hoss and Settle (1990) included larva, juvenile, and adults from benthic to pelagic habitats. Limited information is 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). A dying pygmy sperm whale rescued by the National Aquarium in Baltimore had ingested several pieces of plastic bags and balloons (Craig Vogt, EPA, personal communication to Marine Board staff, August 4, 1994). The Texas Marine Mammal Stranding Network has records of necropsies revealing debris ingestion by several cetaceans. In one highly publicized case, a rough-toothed dolphin died of peritonitis (inflammation of the abdominal lining) attributed to ingestion of a plastic snack food bag, while a 4-ton minke whale died with a plastic bag in its stomach. This information demonstrates that data on the effects of marine debris can be obtained through existing research mechanisms designed to achieve other goals. It might be feasible to expand other research projects focusing on non-Annex V topics, such as fish feeding behavior, to record any ingestion of plastics and other debris. Data also could be gathered by conducting regular necropsies on dead, stranded marine mammals and other animals. The value of using existing procedures to compile and maintain a database on debris interactions with wildlife is demonstrated by a report on plastic ingestion by the West Indian manatee, an endangered species. In the southeastern United States, manatee carcasses routinely are salvaged to determine cause of
