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8 Conclusions and Recommenc/ations CONCLUSIONS he committee has analyzed available data on the five sea turtle species found in U.S. territorial waters to ascertain current popula- tion trends. The most important data were the numbers of nests or nesting females on the nesting beaches, but other useful data were the incidences of turtle strandings and numbers of adults sighted at sea in the course of aerial surveys. Population trends of several species were evident especially from counts of nests and nesting females. The Kemp's ridleys on the nesting beach at Rancho Nuevo, Mexico, have declined to about 1% of their abundance in 1947; since 1978, the number of nesting females has declined from about 700 to an estimated low of only 350 in 1989. This species is obviously the most critically endangered of all the sea turtle species. Counts of loggerheads nesting on various beaches of the south- eastern coasts vary with latitude: numbers of nesting loggerheads on South Carolina and Georgia beaches are declining; but in two study areas in Florida, the numbers seem to be stable in one and appear to be increasing in the other. Green turtles are showing some increased nesting on Hutchinson Island, Florida. Leatherbacks and hawksbills nest too infrequently on southeast beaches for clear-cut trends to be identified. 144
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145 Conclusions and Recommendations As judged from stranding data, the most abundant turtles in U.S. coastal waters are loggerheads; Kemp's ridleys and green turtles are less abundant; and leatherbacks and hawksbills are even less common. Aerial surveys designed to count turtles at sea have yielded less precise num- bers, because many adult turtles and small juveniles are difficult to identi- fy and count accurately from the air. As a result, aerial surveys have been used only sparingly to assess patterns of sea turtle distribution; their results, however, support the belief that loggerheads are the most abun- dant species in both inshore and offshore habitats. Causes of sea turtle deaths, and especially causes associated with declining populations, can be categorized either as natural or related to human activities. Sea turtles have long been harvested for their eggs and meat, for their shells (carved for ornaments), and for their skin (leather) and various body parts (oil-based derivatives). Overexploitation of green turtles for a turtle cannery industry in the Gulf of Mexico as early as the late 1800s was largely responsible for their decline in the early 1900s. A wide range of human activities have been identified as causing sea turtle deaths. Those with effects especially on sea turtle eggs and hatch- lings include various beach manipulations (e.g., fortification, deposition of sand, cleaning), the use of artificial lighting, vehicular and human traf- fic on beaches, and the planting of exotic vegetation. Although mortality data on many of those factors have been found for various sites at vari- ous times, the data are generally too sparse and localized for use in quan- tifying long-term effects on sea turtle species. The committee was better able to quantify human-associated causes of deaths of juvenile and adult sea turtles. Of all the known factors, by far the most important source of deaths was the incidental capture of turtles (especially loggerheads and Kemp's ridleys) in shrimp trawling. This factor acts on the life stages with the greatest reproductive value for the recovery of sea turtle populations. Strong evidence for the effect of shrimp trawling on turtles came from the following findings: · The mortality of turtles caught in shrimp trawls increases markedly for tow times greater than 60 minutes. · Numbers of stranded turtles increase with the opening of shrimp seasons and decrease with the closing of shrimp seasons. · Loggerhead populations declined in areas where shrimp trawling off their nesting beaches was intense, but did not decline in areas where trawling was not intense. · The estimated numbers of sea turtles captured by shrimp trawling are large.
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146 Decline of the Sea Turtles Other fishery operations, lost fishing gear, and marine debris are known to kill sea turtles, but the reported deaths are only about -~0% of those caused by shrimp trawling. Dredging, entrainment in power-plant intake pipes, collisions with boats, and the effects of petroleum-platform removal all are potentially and locally serious causes of sea turtle deaths. However, these collectively amount to less than 5% of the mortality caused by shrimp trawling. Natural diseases and parasites, and toxic sub- stances can and do kill sea turtles, but their overall effects on sea turtle populations cannot be quantified. Sea turtles commonly ingest a wide variety of plastic substances and petroleum residues that can harm them. Although the ingestion of plastics has been observed, the magnitude of resulting mortality cannot be determined from existing information. Natural predation on turtles in all life stages, parasitism, diseases, inclement weather, beach erosion and accretion, thermal stress, and high tides are all known to affect populations adversely, especially on the nest- ing beaches. But the committee concluded that changes in natural sources of mortality are not the causes of observed population declines except in a few localized instances. Thus, the committee identified population declines in sea turtle popu- lations, and it determined that the most important mortality factor has been the incidental capture of subadult and adult sea turtles in shrimp trawls. RECOMMENDATIOINIS Conservafion Measures The committee considered several options for conserving sea turtles. Rather than recommend specific regulations, the committee has focused on various aspects of sea turtle biology and various sources of mortality. Its recommendations are therefore general enough to permit various man- agement options in some cases. However, it is clear to the committee that at least the Kemp's ridley population is dangerously small and that the species needs increased protection. In addition, loggerheads are declining rapidly in South Carolina and Georgia, and green turtles remain uncommon, although they are beginning to show some evidence of pop- ulation increase at one site in southern Florida. All of those species need increased protection under the Endangered Species Act and other relevant legislation.
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147 Conclusions and Recommendations Reducing Incidental Deaths of Juvenile and Adult Sea Turtles Shrimping Incidental deaths due to shrimping must be reduced. An estimated 5,500-55,000 loggerheads and Kemp's ridleys are killed each year by shrimping activities in U.S. waters. The waters off northern Flori- da, Georgia, South Carolina, Louisiana, Mississippi, Alabama, and Texas are most critical, but the committee recommends the use of TEDs in bot- tom trawls at most places and most times of the year from Cape Hatteras to the Texas-Mexico border. At the few places and times where TEOs might be ineffective (e.g., where there is a great deal of debris), alterna- tive conservation measures for shrimp trawling might include tow-time regulations under very specific controls and area and time closures. Restrictions could be relaxed where turtles are and historically have been rare, such as in deeper waters of the gulf. The committee believes that shrimping with adequate controls is com- patible with the recovery of turtle populations. Although prohibition of shrimp trawling might be required as a "last-ditch" measure under the Endangered Species Act, appropriate application of existing technolo- gy-especially TEDs, innovative new technologies, and other conserva- tion measures have the potential to reduce sea turtle mortality to a level that the populations can tolerate. The committee comments here on some of the available controls. · TEDs. The use of TEDs at all times in all areas could theoretically reduce the capture of sea turtles to 3% of the rate seen without TEDs. However, complicating factors, such as the presence of sea- grasses and other debris, reduce the fishing effectiveness of TED- equipped trawls at some times and might even prevent the success- ful ejection of turtles that enter the trawls. The available data do not show conclusively that significant numbers of sea turtles occupy all waters fished by shrimpers throughout the entire year. However, turtles are present in some areas even where TEDs are not now required. For example, current regulations do not require TED use from northern Florida to Cape Hatteras waters after the end of August, but stranding data and aerial-survey data demonstrate that sea turtles, especially Kemp's ridleys, are in fact still in these waters through December and are suffering trawl-related mortality. Tow-time limits. Available data suggest that limiting tow durations to 40 minutes in summer and 60 minutes in winter would yield sea turtle survival rates that approximate those required for the approval of a new TED design. Use of tow-time restrictions would avoid the clogging problems experienced when TEDs are used in areas with abundant debris. The 1987 NMFS regulations appropriately incorpo
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148 Decline of the Sea Turtles rated tow-time limits as an option in inshore waters, where there often is much debris. However, these tow-time regulations need fur- ther refinement. Current tow-time limits are too long, if animals described as comatose in prior reports were in fact destined to die. Also, the current tow-time limits are not properly stratified by season to protect turtles adequately in warm seasons. · Relaxation of TED use and tow-time regulations at selected locations and times. TED use and tow-time limits might be selec- tively applied when and where the probability of capturing sea tur- tles does not exceed acceptable levels. Available information should be examined for the potential of such fine tuning. Because the over- lap between turtle distribution and fishing activities is great, such an approach would have limited applicability, but would perhaps make the regulations less onerous. · Limited time/area closure for turtle "hot spots." Under special circumstances (e.g., in waters adjacent to dense nesting beaches), sea turtle concentrations in defined areas might be temporarily so high, or the turtles so vulnerable, that other conservation measures do not offer adequate protection. Other Human Activities Sea turtle deaths incidental to other human activities such as operation of other fisheries, abandonment of fishing gear, dredging, and oil-rig removal-should be addressed and reduced. Finfish trawls kill some turtles. Groundfish trawls are structurally and operationally similar to shrimp trawls, and their potential effects on sea turtles that encounter them are similar as well. Observer data on rates of sea turtle capture and deaths related to groundfish trawls are not available. The committee recognizes the need for NMFS to assess the effects of gill- net fisheries and the winter groundfish trawl industry on the incidence of turtle capture and mortality. If mortality is substantial, NMFS should con- sider expanding the regulations designed to protect sea turtles from drowning in trawl nets to include all bottom trawls and set nets, not only shrimp trawls. That would protect sea turtles now at risk because of win- ter groundfish trawling and the setting of unattended nets, such as pound nets and gill nets. Research and development should continue, in an effort to reduce fur- ther the loss of sea turtles in hopper dredges. Modification of dragheads to exclude turtles during maintenance dredging appears to be feasible, and research on modifications continues. Continuing surveys of popula- tion numbers and movements within important, frequently dredged entrance channels will provide more understanding of sea turtle behavior that will be applied to improving management designs. Turtles should be relocated away from dredging operations when necessary.
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149 Conclusions and Recommendations The observer program is essential to measure the success of efforts to mitigate the loss of sea turtles in hopper dredges. Finding turtle carcasses or remains in the hopper sediments is difficult, so the on-board observer program should be continued. Although some preliminary work has been done, hopper dredges must be monitored, especially where sea tur- tles might be involved. Other sources of turtle mortality should be reduced. Marine debris and pollutants can kill turtles that ingest them. MARPOL and other programs to reduce marine pollution are in place, and some have recently been strengthened. Sea turtles are affected to some degree by explosions asso- ciated with the building and demolition of marine structures, especially those related to the oil and gas industry. MMS and NMFS programs are under way to reduce these potential impacts. Reducing Directed Harvest of Sea Turtles Directed harvest of all sea turtle species in U.S. waters should continue to be prohibited. Because of the transnational migration and distribution of sea turtles, population recovery would be substantially improved if all directed harvests of sea turtles were eliminated in other countries as well. Reproduction-Relatec! Protection Critical nesting areas, nesting activities, and early life stages (eggs and hatchlings) of each species must be protected. Areas of particular con- cern include beaches between Melbourne Beach and Wabasso Beach, Florida, for loggerheads and the Rancho Nuevo beach in Mexico for Kemp's ridleys. Protection of nesting areas, nesting activities, and eggs and hatchlings is critical to the survival of the Kemp's ridley, and its importance for other species is increasing, in light of continued beach development, land use patterns, and other beach practices. Possible actions include public purchase of undeveloped beaches for restricted, nonthreatening uses; public purchase of development rights for undevel- oped beaches; prohibition of vehicular traffic on beaches during nesting and incubation periods; control of lighting in the vicinity of nesting beaches; predator control; and establishment of a marine park at Rancho Nuevo. The 16 km of undeveloped beach property between Melbourne Beach and Wabasso Beach, Florida, in the Archie Carr National Wildlife Refuge proposed by the U.S. Fish and Wildlife Service, should be protect- ed. Purchase of the land is the best method to ensure protection. The lands are available, and action should be taken before they are developed.
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150 Decline of the Sea Turtles Small-scale, research-based captive breeding programs for Kemp's rid- leys should be continued. Refinement of the technique would ensure the maintenance of a gene pool in captive animals in the event of a population loss. However, this option is not considered a promising management tool for the restoration of wild populations, because small populations of cap- tive animals lack much of the genetic variability that was available in the wild population. In addition, the development of various survival behav- iors, for example, feeding, nesting, and migration, might be impaired. Headstarting should be maintained as a research tool, but cannot substi- tute for other essential conservation measures. The headstarting experi ment should be continued, because it has research and public-awareness value. Experimental methods must continue to be improved. However, present knowledge makes it clear that headstarting, even if it works, will not be effective without simultaneous implementation of other conservation measures to reduce human-related deaths of juvenile and adult sea turtles. Research Sea Turtle Biology In the process of evaluating the status of sea turtles, some knowledge gaps became apparent. Important data are missing some difficult (or impossible) to obtain, some less so-that are imperative to good manage- ment. Current knowledge of sea turtles has allowed us to evaluate and recommend some basic research and conservation measures in this report so that further protection and recovery of sea turtle populations can be implemented. Demographic Models For no species of sea turtle is knowledge of age- specific survivorship and age-specific fecundity adequate. Enough is known, however, about loggerhead demography to provide a fundamen- tal understanding of basic concepts, such as the relative reproductive value of various life history stages. To evaluate fully the comparative importance of different sources of mortality and to evaluate the effective- ness of conservation measures, better information is needed on age at reproductive maturity, age-specific survivorship, age-specific fecundity, and their variances. Therefore, the committee recommends research on: · Age-specific fecundity and survivorship, through enlargement of existing tagging programs and creation of new ones; special atten- tion must be given to the tag-loss problem. · Life stages and sex ratios, through increased efforts to count sea tur- tles of all age groups in as many habitats as possible; mortality esti- mates for all life stages are important.
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151 Conclusions and Recommendations Sec Turtle Distribution Information is needed on foraging habitats of sea turtles in deep water and the use of shallow water by juveniles and subadults. Sampling areas and times should be chosen to permit replica- tion with the best current technology. Such surveys should help to define the amount of overlap of national jurisdictions and assist the implementa- tion of cooperative programs, such as that between the United States and Mexico for the Kemp's ridley. Sec Turtle Physiology and Pathology More information is needed on the effects on turtles of ingesting plastics, of petroleum products, of forced prolonged immersion, of cold-water stunning, of underwater explosions, and of oceanic debris. The committee recommends selected, complete necropsies to determine pathological conditions, causes of wounds, and any other cause of death. Research should also ascertain turtles' abilities to ingest plastics of various types and sizes without adverse effect. The effects of floating petroleum products on the repro- ductive and feeding behavior of turtles should be studied. To allow for the complete evaluation of the use of tow-time limits in trawl fisheries, research should address how enforced submergence affects sea turtle anatomy and physiology as a function of season, water temperature, species and size, time of day, and history of previous forced submergence. Improved resuscitation techniques of comatose turtles should be developed from such research. The effect of explosives on sea turtles during construction and demoli- tion of marine structures or for any other reason (such as military ord- nance) is largely unknown and must be investigated. Research should focus on the distribution and abundance of sea turtles near platforms des- ignated for removal by explosives, confirmation and necropsy of dead turtles near explosion sites, the feasibility of moving turtles to different sites, and behavior of animals at explosion sites. Research on the reproductive biology of sea turtles in the wild should continue. Management Techniques More research and experimentation are needed to improve TEDs and explore new alternatives. The techniques of deploying TEDs in a variety of conditions also need improvement. For example, it is important to reduce the tearing of trawl nets that have TEDs. If TEDs can be modified to allow efficient fishing for shrimp when seagrass and other algal detritus or other debris are abundant, a major objection to the use of TEDs by shrimp fishermen could be addressed. All these management techniques and options should include input from shrimp fishermen and gear experts. Enhancing acceptance of regulations on the shrimp fishing
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152 Decline of the Sea Turtles industry would enhance compliance and promote sea turtle conservation, and research should focus on whether education on TED use would be helpful in this regard. Research should also address other inducements to increase compliance with TED regulations. There are strong grounds for believing that the drowning of sea turtles in trawls can be greatly reduced by the adoption of certain controls on the shrimp fishery, but it is important to evaluate the effectiveness of any regulations that are adopted. Because the shrimp fisheries are regulated to open and close at various specified dates at many places, the commit- tee was able to use the timing of the fishery to test the impact of shrimp trawling on the numbers of stranded sea turtles. This test produced strong evidence that shrimp trawling at some places and times is responsible for 70-80% of the sea turtles found stranded on the beaches of Texas and South Carolina. In contrast, the committee was not able to develop similar tests of the degree to which plastic debris, oil pollution, and other factors affect the survival of sea turtles. The characteristics of the shrimp fishery that helped identify its effect on turtles should be used to test the effectiveness of the regulations. His- torical data on the relationship of the numbers of stranded sea turtles to the opening and closing of the shrimp fishery in Texas and South Caroli- na should be collected in future years to evaluate the degree to which the drowning of sea turtles in trawls is reduced by the regulations. Further research is necessary to assess the effectiveness of tow-time limitations. For example, are shrimp trawlers ever so concentrated that they repeatedly catch individual sea turtles often enough to make tow- time limits ineffective? Even though sea turtles can survive enforced sub- mergence for some time, repeated submergence can cause drowning. Shrimp trawlers could help to answer the question by using carapace marks to denote captures and recaptures and then assessing turtle survival as a function of capture frequency during relatively short periods (e.g., a day). The results of the physiological research described above would also help. The impact of fishing practices other than shrimp trawling on sea tur- tles might be large, but it is not well known. Research is needed on the impact of groundfish trawling, set-net and long-line fishing, gill nets, and pound-net fishing on sea turtles at different times and places. Research on the complex effects of artificial protection of early life stages of sea turtles is needed. Special efforts should be directed to reproductive biology of captive sea turtles and the effects of rearing them in closed culture. Young turtles just out of captivity might not be pre- pared to survive in the wild. Research on means of acclimation of nurs- ery-reared sea turtles would be profitable. How long should sea turtles be reared in captivity to maximize their ultimate survival in the wild? Is it
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153 Conclusions and Recommendations worth taking an egg from a beach to raise the turtle in the nursery? It is not known whether female sea turtles are imprinted to nest on the beach where they were released. That information is needed before the place of release of nursery-reared turtles is determined. The cumulative effects of human activities on nesting beaches should be quantified relative to the total available nesting areas, because the loss of nesting beaches through development or alteration could extirpate local populations. More research is needed on how to control or alter artificial lighting along nesting beaches, to minimize interference with nesting and with the crawl to the sea by emerging hatchlings. The impacts of motor vehicles on beaches, erosion control measures, and the development of beachfront property needs to be evaluated more com- pletely.
Representative terms from entire chapter: