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SOURCES, FATES, AND EFFECTS OF SHIPBORNE GARBAGE 56 death and collect biological information. In Florida, personnel from the U.S. Fish and Wildlife Service and the University of Miami have performed systematic necropsies on dead manatees. Based on this information, Beck and Barros (1991) found that of 439 manatees necropsied between 1978 and 1986, 63 (14.4 percent) had ingested debris. Pieces of monofilament fishing line were the most common debris items ingested. (Marine debris is not, however, the leading cause of manatee deaths, which are attributed most often to collisions with vessel propellers.) Ghost Fishing Ghost fishingâa term referring to lost or discarded fishing gear that continues to catch finfish and shellfish species indefinitelyâmay significantly reduce some commercial stocks and ultimately could affect marine ecosystems. This is a difficult problem to study. Few data are available on the number of gear units deployed in various fisheries, the number lost, or the capability of various types of gear to ghost fish (Natural Resources Consultants, 1990). Nevertheless, available estimates suggest that ghost fishing could be a significant problem. Lobster and crab traps and gillnets have been found to have a significant potential to ghost fish. For the inshore lobster fishery of Maine, it has been estimated that 25 percent of all traps are lost each year, and that each lost trap can continue to catch lobsters up to 1.1 kg (2.5 lbs.) (Smolowitz, 1978). An estimated 10 to 20 percent of traps used in the coastal Dungeness crab and American lobster fisheries are lost each year; many crab and pot fisheries now are required to mark traps and use timed-release devices on panels to minimize ghost fishing (Breen, 1990). Lost gillnets can capture many fish and shellfish over long periods of time. According to one estimate, lost gillnets can fish at a 15 percent effectiveness rate for up to eight years (Natural Resources Consultants, 1990). A 24-day gillnet retrieval project in 1976 recovered 176 nets containing 4,813 kg (10,611 lbs.) of groundfish and 2,593 kg (5,717 lbs.) of crab (Brothers, 1992). A report of 10 lost nets found in 37.5 hours of searching off Massachusetts (Cart, 1986) suggests there may be numerous lost nets in some sink gillnet fishing areas in the northeastern United States (Laist, 1994). SUMMARY This chapter yields four basic findings, which provide the foundation for the remainder of the report. The first three findings are straightforward. First, considerable amounts of garbage are generated by seafarers in most if not all maritime communities. Second, garbage discarded into the sea can be transported far from the point of discharge. Third, the disposal of plastics in the marine environment is causing considerable harm, including mortality among marine mammals, turtles, birds, and fish, either through entanglement or ingestion.
