Chapter VI 



IMPACTS OF MARINE DEBRIS 



Plastic and other synthetic material lost or inten- 

 tionally discarded into the marine enviroimient kills 

 and injures significant numbers of many marine spe- 

 cies, including marine mammals. For example, 

 derelict fishing nets and traps, rope and line, strapping 

 bands, and other such debris may attract and entangle 

 or accidentally entangle marine mammals, seabirds, 

 turtles, fish, and crustaceans. Marine animals also 

 confuse floating plastic bags, small plastic fragments, 

 and other debris with natural prey and ingest them. 



Among the animals affected are species listed as 

 endangered or threatened, and commercially valuable 

 crustaceans and fish. Indeed, marine debris kills 

 some of the country's most imperiled marine species 

 (e.g., Hawaiian monk seals, right whales, West Indian 

 manatees, and Kemp's Ridley and green sea turtles) 

 and its most commercially valuable species (e.g., 

 lobsters and king crabs). Marine debris also poses 

 serious health, safety, and navigation hazards for 

 humans and causes aesthetic impacts that are costly to 

 clean up. 



Since the early 1980s, the Marine Mammal Cora- 

 mission has played a major role in focusing domestic 

 and international attention on the need to assess and 

 mitigate wildlife problems caused by marine debris. 

 Among other things, the Commission provided initial 

 fiinding and terms of reference for the first interna- 

 tional symposium on marine debris in 1984. These 

 and other past efforts are discussed in previous 

 Annual Reports. Activities undertaken by the Com- 

 mission and others in 1991 are discussed below. 



Background 



The amount of debris in many coastal and open- 

 ocean areas has increased dramatically since the 



1950s. At least three factors appear to have contribut- 

 ed to this trend. First, synthetic materials that de- 

 grade slowly in sea water are being used more and 

 more in manufactured items commonly lost or dis- 

 carded at sea. As a result, the total debris load in a 

 given area at a given time reflects the amount of 

 synthetic material lost and discarded over a signifi- 

 cantly longer period of time than was the case when 

 natural fibers predominated prior to the 1950s. 

 Second, because synthetic materials often cost far less 

 than the natural materials they replaced and because 

 many items are now made for one-time use (e.g., 

 plastic bags, bottles, cups, etc.), economic incentives 

 for re-using or recycling are reduced. Third, the 

 number of ships and coastal residents that lose or 

 discard debris have increased substantially. 



As the amount of synthetic debris increases, so too 

 does its threat to wildlife. Marine animals that 

 become entangled in loops or openings of marine 

 debris may drown, lose their ability to catch food or 

 avoid predators, or incur wounds and infections from 

 the abrasion of attached debris. Those that ingest 

 objects made of synthetic materials may have digestive 

 tracks blocked, stomach linings damaged, or feeding 

 drives reduced by a false sense of satiation. Because 

 of their increased durability and strength, synthetic 

 materials are more likely to kill or injure animals than 

 natural materials used previously. That is, plastic 

 sheeting is more likely than paper to remain lodged 

 for long periods in an animal's digestive tract, and 

 monofilament nets will retain their ability to entangle 

 and kill animals much longer than cotton netting. 



Until recently, the magnitude of such effects has 

 been masked by the size of the ocean, the deceptively 

 simple nature of the threat, the erroneous perception 

 that encounters between marine mammals and debris 

 are unlikely, and the apparent absence of large num- 



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