1998 Year of the Ocean ^Ocean Living Resources 



Indirect fishing impacts 



The most significant indirect impacts of fishing on marine biodiversity include bycatch, 

 habitat destruction and ancillary impacts on interacting species or ecosystems (NRC 1995). 

 Bycatch is the capture and associated mortality of nontarget species or of the mortality of the 

 target species that are discarded because of size, quality, or other preferences. For example, in the 

 southeast U.S. shrimp fishery, for every pound of landed shrimp, approximately 4-5 pounds of 

 non-target species (mostly juvenile fish) are also captured and mostly discarded. The high level 

 of bycatch in shrimp trawls has contributed to the closure of some commercial fisheries in the 

 Gulf of Mexico. Bycatch is also a major concern for endangered or threatened species — e.g., sea 

 turtle bycatch in shrimp fisheries; marine mammal drowning in gillnets; and shark, seabird, and 

 sea turtle bycatch in longline fisheries. It is estimated that the unregulated longline fisheries for 

 toothfish in the Southern Ocean may have contributed to the incidental mortality of 66,000 to 

 100,000 seabirds in 1997 alone (CCAMLR 1997). 



By its very operation, fishing changes the relationships among species in a marine 

 foodweb. It can change the functioning of a marine system by altering the composition of a 

 particular marine community — either by simply removing large amounts of all types of 

 organisms, as in the shrimp example above, or by taking large numbers offish of a certain age or 

 size from a system. For example, in the Georges Bank/Gulf of Maine fishery, the "bottom fish" 

 species of cod, hake, flounder, and haddock were severely overfished resulting in their 

 replacement by commercially less valuable fish species (i.e., skates and dogfish). The ensuing 

 ecosystem shift may preclude the recovery of the cod fishery, despite a stable but much reduced 

 biomass for this species. 



Marine fisheries may alter or destroy habitats. Fishery practices that can harm habitats 

 include bottom trawling, blast fishing, and the use offish traps and poisons on coral reefs. 

 Bottom trawls can be particularly destructive, with impacts on benthic habitats and invertebrate 

 communities lasting for many years (Jones 1992). Habitat destruction is extensive and may 

 contribute to the decline offish and other species; yet because the destruction is hidden below the 

 surface, it is seldom well documented or quantified. 



Chemical Pollution and Eutrophication 



Land-based sources are estimated to account for more than 75 percent of the pollutants 

 entering the world's ocean. Human communities daily generate new pollution that further 

 degrades already diminished ecosystems. Some forms of pollution originate hundreds of miles 

 inland and are carried to the sea by rivers or through the air. Point sources originate from a 

 specific place, such as an industrial facility or municipal sewage treatment plant. Non-point 

 sources originate from dispersed areas, such as agricultural lands (silt, pesticides, fertilizers, and 

 animal wastes), roadways and other paved surfaces (hydrocarbons), deforested hillsides (silt), 

 septic tanks, and atmospheric deposition. These sources cause at least as much harm to marine 

 living resources as do point sources, but are generally much more difficult to address. 



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