Chapter VIII 



IMPACTS OF MARINE DEBRIS 



Over the past 40 years the increasing amount of 

 plastic and other synthetic materials lost and discarded 

 into the marine environment has become a major new 

 form of marine pollution throughout the world. In 

 addition to its socioeconomic impacts — posing 

 hazards to human health and safety, imposing eco- 

 nomic constraints on tourism and commercial fisher- 

 ies, and creating financial burdens for coastal commu- 

 nities that must clean it up — marine debris causes 

 mortality and serious injury to marine mammals, 

 seabirds, sea turtles, fish, and shellfish. 



As discussed in previous annual reports, the latter 

 concern prompted the Marine Mammal Commission 

 to assume an important role in bringing marine debris 

 pollution to the attention of responsible agencies and 

 in precipitating responsive domestic and international 

 action. This chapter discusses the nature of the 

 problem and recent actions taken by the Commission 

 to address the issue. 



Biological Impacts of Marine Debris 



Biological impacts of marine debris on marine 

 animals take two forms: entanglement and ingestion. 

 In both cases, these interactions are magnified by 

 factors that attract animals to marine debris. For 

 example, debris sometimes resembles natural prey. In 

 other cases, predators are attracted to vulnerable prey 

 items already caught in debris or using debris as a 

 source of cover. Once entangled, animals that are 

 unable to free themselves quickly are likely to exhaust 

 themselves and drown, incur infections from the 

 abrasion of attached debris, have their ability to catch 

 food impaired, or be unable to avoid predators. 

 Animal that ingest debris items may have their diges- 

 tive tracks blocked or injured. 



As a contribution to the Third International Confer- 

 ence on Marine Debris in Miami, Florida, on 8-13 



May 1994, a member of the Marine Mammal Com- 

 mission staff reviewed information on the biological 

 impacts of marine debris. The results demonstrated 

 that marine debris is a broadscale pollutant that affects 

 many of the world's marine species. As shown on 

 Table 11, marine debris entanglement or ingestion 

 records have been reported for at least 267 species, 

 including at least 43 percent of the world's marine 

 mammal species, at least 44 percent of the world's 

 seabird species, all but one of the world's seven sea 

 turtle species, and at least 68 species of fish and 

 shellfish, many of which are commercially important. 



In general, death and serious injury of marine life 

 are far more likely to occur as a result of entangle- 

 ment and entrapment in debris than by ingestion. In 

 this regard, most entanglement reports involve derelict 

 fishing gear, including both intact gear and smaller 

 fragments of netting, rope, and monofilament line. 

 Strapping bands, such as those used to bind bait boxes 

 and cargo, are also a significant entanglement hazard. 

 The principal cause of ingestion-related deaths is 

 blockage of digestive tracks by plastic sheeting, plastic 

 bags, or balloons. Ingestion-related deaths are report- 

 ed most frequently for sea turtles but also occur in 

 cetaceans and manatees. Small plastic pellets and 

 plastic fragments are also common in the stomachs of 

 some seabird and sea turtle species; however, the 

 effect of ingesting these items is less apparent. 



While there is clear evidence that animals of many 

 marine species actively seek out and interact with 

 marine debris, efforts to quantify the frequency of 

 such interactions and their impact at a population level 

 have been frustrated by difficult, unresolved sampling 

 problems. For example, documentation of interac- 

 tions at sea is rarely feasible because both the debris 

 and the affected animals are scattered across vast areas 

 and are very hard to detect. In addition, animals 

 killed by marine debris tend to sink or be eaten 

 quickly, confounding study efforts. Most studies 



161 



