Decline of the Sea Turtles Causes and Prevention (1990) / Chapter Skim
Currently Skimming:
Executive Summary
Executive Summary
Pages 1-15
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For some major populations and species of sea turtles to persist, substantial progress in conservation will have to be made. Concerns about the continuing declines of sea turtle populations and the potential impact of new gear regulations on commercial shrimp trawlers prompted the Congress to add a provision to the Endangered Species Act Amendments of 1988 mandating an independent review by the National Academy of Sciences of scientific and technical information pertaining to the conservation of sea turtles.
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This report presents scientific and technical information on the population biology, ecology, and reproductive behavior of five endangered or threatened species of sea turtles. It evaluates population declines, causes of turtle mortality, and the effectiveness of past and current mitigation efforts, and recommends conservation measures to protect or increase turtle populations.
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SEA TURTLE POPUIATION TRENDS Changes in sea turtle populations are most reliably indicated by changes in the numbers of nests and nesting females on the nesting beaches. Females return to the same beaches repeatedly and are relatively easily counted there.
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waters. NATURAL MORTAUh OF SEA TORTES AND REPRODUCTIVE VALUE OF UFE STAGES Mature female sea turtles lay many clutches of eggs during their lifetimes with about 100 eggs per clutch, but only about 85% of the undisturbed eggs produce hatchlings, and most of the hatchlings probably die in their first year.
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The committee concluded that conservation measures directed at large juveniles and adults are especially critical to the success of sea turtle conservation. SEA TURTLE MORTAUh ASSYRIAN WITH HUMAN ACTIVITIES All life stages of sea turtles are susceptible to human-induced mortality.
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Atlantic shrimping effort is concentrated off South Carolina, Georgia, and northern Florida. Several lines of strong evidence make it clear that sea turtle mortality due to incidental capture in shrimp trawls is large: · The proportion of dead and comatose turtles in shrimp trawls increases with tow time of the trawl from very few at 40 minutes to about 70% after 90 minutes.
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Other Fisheries Mortality associated with other fisheries and with lost or discarded fishing gear is much more difficult to estimate than that associated with shrimp trawling, and there is a need to improve the estimates. A few cases stand out, such as the possible turtle losses from the winter flounder trawl fishery north of Cape Hatteras (about 50-200 turtles per year)
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The occurrence of plastic debris in the digestive tracts of sea turtles is common; for example, half the turtles that stranded on Texas beaches in 1986-1988 and one-third of the leatherbacks and onefourth of the green turtles from the New- York Bight area necropsied in 1979-1988 had plastic debris in their digestive tracts. The food preferences of the leatherback (jellyfish)
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The committee was unable to make quantitative estimates of mortality from these sources, but the impact of ingesting plastics or debris could be severe. SEA TURTLE CONSERVATION The committee considered conservation measures applicable to the two habitats of sea turtles most vulnerable to human-associated mortality: the beaches (eggs, hatchlings, and nesting females)
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Intentional harvest of sea turtles and their eggs continues to occur throughout the Caribbean region, including Puer to Rico. Recluction of Unintentional Bycatch Sea turtle deaths caused by unintentional capture in shellfish and finfish fisheries can be reduced by limiting fishing effort at some times and places, closing a fishery, modifying fishing gear to exclude turtles or, for
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in bottom trawls and smaller mesh size in pound-net leaders, can reduce turtle deaths. Fishery closures can be effective, as demonstrated in the case of the sturgeon fishery off the Carolinas and as evidenced by the maintenance of sea turtle nesting rookeries in the south Atlantic coast of Florida, where there is very little shrimp fishing.
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Use of tended barrier nets to remove sea turtles could reduce this small source of mortality. Plastics and Debris The best conservation measures to reduce ingestion of plastics and debris are measures that reduce ocean dumping of such materials from ships and land sources.
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2. Natural mortality factors such as predation, parasitism, diseases, and environmental changes are largely unquantified, so their respective impacts on sea turtle populations remain unclear.
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Available data suggest that limiting tow times to 40 minutes in summer and 60 minutes in winter would yield sea turtle survival rates that approximate those required for approval of a new TED design. Restrictions could be relaxed where turtles are and historically have been rare.
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6. Efforts to improve TED technology and explore other methods to conserve sea turtles should be continued, including research on the effect tiveness of regulations.
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