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Executive Summary ive species of sea turtles regularly spend part of their lives in U.S. coastal waters of the Atlantic Ocean and the Gulf of Mexico: Kemp's ridley, loggerhead, green turtle, hawksbill, and leatherback. They are ancient reptiles, having appeared on earth millions of years before humans. Sea turtles were widely used by humans in earlier times for food, ornaments, and leather, and they still are used in these ways by many societies. They are now endangered or threatened and are protected under the Endangered Species Act. Kemp's ridleys, leatherbacks, and hawksbills are listed as endangered throughout their ranges; green turtles are endangered in Florida, and threatened in all other locations; loggerheads are listed as threatened throughout their range. 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. The Congress further man- dated review of the causes and significance of turtle mortality, including that caused by commercial trawling. Accordingly, a study committee was
2 Decline of the Sea Turtles convened by the National Research Council's Board on Environmental Studies and Toxicology in collaboration with its Board on Biology. The committee included experts in international and domestic sea turtle biolo- gy and ecology, coastal zone development and management, commercial fisheries and gear technology, marine resources, and conservation biolo- gy. During the course of the committee's 1-year study, it heard from rep- resentatives of the shrimping industry, conservation organizations, the U.S. Fish and Wildlife Service, the National Marine Fisheries Service, and Sea Grant programs. The committee observed shrimp trawling exercises with and without turtle excluder devices on a converted shrimp trawler in Georgia coastal waters. It reviewed pertinent published literature and analyzed original data sets on aerial and beach turtle surveys, shrimp trawling efforts, other commercial fisheries, turtle strandings, and other materials from a variety of organizations and knowledgeable individuals. This report presents scientific and technical information on the popula- tion 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 tur- tle populations. The committee was not charged or constituted to address and did not analyze social and economic issues related to sea turtle con servation. MULE HISTORIES OF SEA ROTS The five species of sea turtles considered in this report have similar life histories. Females of all five species lay clutches of about 100 eggs and bury them in nests on coastal beaches. Mature male and female sea tur- tles aggregate off the nesting beaches during the spring to mate, and females might return to the beach to deposit 1 to 10 clutches in a season. Individual Kemp's ridleys probably nest each year after reaching maturity; females of the other species routinely nest every 2-4 years. After an incubation period of about 2 months, hatchlings of all the species dig their way to the surface of the sand and scramble over the beach in their short trip to the ocean. Once in the water, they swim off- shore and spend their early life near the surface in the offshore waters of the Atlantic or Gulf of Mexico. After a few years, most species enter the coastal zone or move into the bays, river mouths, and estuaries, where they spend their juvenile life, eating and growing until they reach maturity some 10-50 years later. Mature sea turtles usually weigh 35-500 kg. Food habits differ among species. Kemp's ridleys prefer crabs, logger- heads eat a wide range of bottom-dwelling invertebrates, green turtles eat
3 Executive Summary bottom-dwelling plants, leatherbacks prey on jellyfish in mid-water, and hawksbills specialize on bottom-dwelling sponges. SEA TURTLE DISTRIBUTION AND ABUNDANCE fudged from strandings of carcasses on beaches from the Mexican bor- der to Maine, the most abundant sea turtles in U.S. coastal waters are log- gerheads, followed by Kemp's ridleys, green turtles, leatherbacks, and hawksbills. According to aerial surveys, large loggerheads are most abun- dant off the coasts, and leatherbacks are about one-hundredth as abun- dant as loggerheads in the Atlantic. In general, other adult turtles and smaller juveniles are difficult to see and identify from the air. One of the two largest loggerhead rookeries in the world is concentrat- ed along the Atlantic beaches of central and southern Florida, but logger- heads nest from southern Virginia to eastern Louisiana. Aerial surveys have identified large concentrations of loggerheads off their primary nest- ing beaches in Florida during the spring and summer; sightings off the nesting beaches are much less frequent during the autumn and winter. Regular nesting of green turtles and leatherbacks also occurs on the Atlantic beaches of central and southern Florida. Kemp's ridleys and hawksbills do not make important use of U.S. coastal beaches, except for hawksbills in the U.S. Caribbean islands. Based on limited trawling data in the gulf, juvenile and adult sea tur- tles off the South Atlantic and gulf coasts are more abundant in waters less than 27 m deep than in deeper waters. Limited aerial surveys in the gulf reveal they are more abundant in waters less than 50 m. Data on depth distribution are scarce, but turtle density during shrimping seasons is apparently about 10 times greater in shallow than in deeper waters. 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 relative- ly easily counted there. For trend analysis, the incidence of carcass strandings on the beaches and the number of adults sighted at sea from airplanes are much less satisfactory, because of uncontrolled variables and uncertainties. The results of population-trend studies are clear in several important cases. Kemp's ridley nesting populations have declined to about 1% of their abundance in 1947 at their only important nesting beach, Rancho
4 Decline of the Sea Turtles Nuevo, on the Mexican coast of the Gulf of Mexico. Since 1978, the num- ber of Kemp's ridley nests has been declining at about 14 per year; the total number of nesting females currently might be as low as 350 (although clearly there are additional turtles in the population: juveniles and males). Loggerhead populations nesting in South Carolina and Georgia are declining, but populations on parts of Florida's Melbourne Beach and Hutchinson Island apparently are not declining, and the Hutchinson Island population might even be increasing. Green turtles nesting on Hutchinson Island are increasing. Data are insufficient to determine whether other populations in U.S. waters are increasing or decreasing. Data available on hawksbills or leatherbacks do not show clear-cut trends in U.S. waters. NATURAL MORTAUh OF SEA TORTES AND REPRODUCTIVE VALUE OF UFE STAGES Mature female sea turtles lay many clutches of eggs during their life- times with about 100 eggs per clutch, but only about 85% of the undis- turbed eggs produce hatchlings, and most of the hatchlings probably die in their first year. The greatest source of natural mortality of these eggs and hatchlings is predation, primarily by carnivorous mammals, birds, and crabs in and on the beaches and by birds and predatory fishes in the ocean. Shoreline erosion of dunes and inundation (drowning) of nests are other important sources of natural mortality. Various causes of sea turtle mortality associated with human activities (artificial lighting, coastal development, etc.) are usually an important component of total mortality. As juvenile turtles in the shallow coastal zone reach a larger size (58-79 cm long), natural mortality rates are expected to decline. A female logger- head probably reaches maturity at about 20-25 years, remains reproduc- tively active for another 30 years or so, and produces a very large number of eggs during her lifetime. The consideration of age-specific natural mortality and reproduction leads to the important concept of reproductive value for each of a turtle's life stages. Reproductive value is a measure of how much an individual at a particular stage of life contributes to the future growth or mainte- nance of the population. An analysis of reproductive value provides valu- able insight for decision makers responsible for the conservation of sea turtles, because it indicates which individuals contribute most to future populations and also where protection is likely to be the most effective. One life-stage analysis of reproductive value for eggs and hatchlings, small juveniles, large juveniles, subadults, and nesting adults used logger
5 cecutive Summary heads at Little Cumberland Island, Georgia, as the example. It was con- cluded that the key to improving the outlook for Georgia and Carolina nesting loggerhead populations lies in reducing the mortality in the older stages, particularly the large juveniles 58-79 cm long. Because the repro- ductive value of the earliest stage was so very low compared with the older stages, protecting 100% of the eggs and hatchlings was not sufficient to reverse the decline in the numbers of nesting females of this model population. It was also noted that the 58-79 cm group of large juveniles is the size class that dominates in the distribution of stranded carcasses on beaches from northern Florida to North Carolina. The committee concluded that conservation measures directed at large juveniles and adults are especially critical to the success of sea turtle con- servation. SEA TURTLE MORTAUh ASSYRIAN WITH HUMAN ACTIVITIES All life stages of sea turtles are susceptible to human-induced mortality. Direct human manipulations such as beach armoring, beach nourish- ment, beach lighting, and beach cleaning-can reduce the survival of eggs and hatchlings in and on the beaches. The presence of humans on the beach, on foot or in vehicles, can adversely affect nesting, buried eggs, and emerging hatchlings. Other factors, such as beach erosion and accretion, or the introduction of exotic plants and predators, are indirect effects of humans that can be responsible for many turtle deaths. However, the committee's analyses led it to conclude that for juveniles, subadults, and breeders in the coastal waters, the most important human- associated source of mortality is incidental capture in shrimp trawls, which accounts for more deaths than all other human activities combined. The committee estimated that mortality from shrimping lies between 5,000-50,000 loggerheads and 500-5,000 Kemp's ridleys each year. Collec- tively, other trawl fisheries; fisheries that use passive gear, such as traps, gill nets, and long lines; and entanglement in lost or discarded fishing gear and debris are responsible for an additional 500-5,000 loggerhead deaths and 50-500 Kemp's ridley deaths a year. Although those numbers are an order of magnitude lower than the losses due to the shrimp fish- eries, they are important. Next in importance are the deaths due to dredging, and collisions with boats: an estimated 50-500 loggerheads each and 5-50 Kemp's ridleys each. Oil-rig removal could account for 10-100 turtle deaths per year, and deaths from intentional harvest of turtles in U.S. coastal waters and entrainment by electric power plants are judged
6 Decline of the Sea Turtles each to be fewer than 50 per year. Deaths resulting from ingestion of plastics and debris and from accumulation of toxic substances, especially from ingested petroleum residues, could be important, but the committee was unable to quantify them. The estimates of human-associated sea turtle deaths are most certain for shrimp fishing and power-plant entrainment; they are less certain for dredging, and least certain for other fisheries, collisions, oil-rig removal, intentional harvest, and ingestion of plastics or debris. In some cases, although direct estimation is impossible, worst-case estimates provide an upper limit on the potential mortality associated with oil-rig removal and collisions with boats. In some cases, conservation measures are in place or are being implemented, and these will lower the above estimates. The Shrimp Fishery The U.S. shrimp fishery is a complex of fisheries from Cape Hatteras, North Carolina, to the Mexican border in the gulf. Those fisheries harvest various species of shrimp at various stages in their life cycles, using a variety of vessels that range from ocean-going trawlers to small vessels operating in nearshore or inside waters. About one-third of the shrimp- ing effort occurs in bays, rivers, and estuaries; t~vo-thirds occurs outside the coastline. Ninety-two percent of the total effort is in the gulf; most of that is in waters shallower than 27 m. The fishing areas off the coastal beaches of Texas and Louisiana account for 55% of the total U.S. effort and 83% of the effort off the coastal beaches. In the Atlantic, 92% is within 5 km of shore. One important nesting area for turtles, where almost no shrimping effort occurs, is the central to southern portion of the Atlantic coast of Florida. 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. The number of stranded carcasses on the beaches increases step- wise by factors of 3.9 to 5 when shrimp fisheries open in South Car- olina and Texas, and decreases stepwise when a shrimp fishery closes in Texas. The data suggest that 70-80% of the turtles strand- ed at those times and places were caught and killed in shrimp trawls.
7 E'cec?~tive Summary · Loggerhead nesting populations are declining in Georgia and South Carolina, where shrimp fishing is intense, but are not declining and might even be increasing farther south in central and southern Flori- da, where shrimp fishing is rare or absent. The committee is aware that these interactions are complex. A much-cited estimate of shrimping-related mortality, 11,000 logger- heads and Kemp's ridleys per year in U.S. coastal waters of the Atlantic and the gulf, was judged by this committee to be an under- estimate, possibly by as much as a factor of 4. This maximal value of 44,000 falls within the order of magnitude estimates by the com- mittee that the number of loggerheads and Kemp's ridleys killed annually lies between 5,500 and 55,000. The estimate of 11,000 tur- tles killed annually was based on analysis that did not account for mortality in bays, rivers, and estuaries, even though many turtles and one-third of the shrimping effort occurs there. The estimate was also based on the assumption that all comatose turtles brought up in shrimp nets would survive. Recent observations have suggest- ed that many (perhaps most) comatose turtles will die and should be included in the mortality estimates until effective rehabilitation methods are available and used. · In North Carolina, turtle stranding rates increase in the summer south of Cape Hatteras while the shrimp fishery is active there, and in the fall and winter north of Cape Hatteras while the flounder trawl fishery is active there. That observation suggests that the flounder fishery might be another source of mortality north of the cape in the fall and winter. Other Fisheries Mortality associated with other fisheries and with lost or discarded fish- ing 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); the historical Atlantic sturgeon fishery, now closed, off the Carolinas (about 200 to 800 turtles per year); and the Chesapeake Bay passive-gear fish- eries (about 25 turtles per year). Considering the large numbers of fish- eries from Maine to Texas that have not been evaluated and the problems of estimating the numbers of turtles entangled in the 135,000 metric tons of plastic nets, lines, and buoys lost or discarded annually, it seems likely that more than 500 loggerheads and 50 Kemp's ridleys are killed annually by nonshrimp fisheries.
8 Decline of the Sea Turtles Dredging Estimates of the mortality of sea turtles taken in dredging operations range from 0.001 to 0.1 per hour. If it takes 1,000 hours of dredging to maintain each navigation channel each year, one to 100 turtles could be killed per active channel in areas frequented by turtles. The 0.1 per hour might be an unrealistically high estimate, and some conservation mea- sures are in place, so the number of turtles killed per channel is probably much less than 100 per year. Boot Collisions Boat collisions with turtles are evident from damage to turtles that strand on coastal beaches. Many of them could have been dead before they were hit, but not all turtles hit and killed by boats drift ashore. The committee estimates that a maximum of 400 turtles per year are killed by collisions off the coasts, but the estimate is very uncertain and unknown for inside waters. Oil Platforms About 100 oil platforms in the western gulf are scheduled for removal each year for the next 10 years. The probability of there being at least one turtle within the damage zone (i.e., within 1,000 m of an explosion to remove a rig) is estimated to be between 0.08 and 0.50. That yields a minimal estimate of 8-50 turtle deaths per year. This estimate might be low, because it is based only on aerial sightings of turtles, or high, because rigs will be surveyed and attempts made to move turtles out of the region before rig removal. Plastics and Debris About 24,000 metric tons of plastic packaging is dumped into the ocean each year. 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 one- fourth of the green turtles from the New- York Bight area necropsied in 1979-1988 had plastic debris in their digestive tracts. The food prefer- ences of the leatherback (jellyfish) and green turtle (bottom plants), in particular, could make them especially susceptible to ingestion of plastic bags. Ingestion of plastics could interfere with food passage, respiration,
9 E:'cecutive Summary and buoyancy and could reduce the fitness of a turtle or kill it. Floating plastics and other debris, such as petroleum residues drifting on the sea surface, accumulate in sargassum drift lines commonly inhabited by hatch- ling sea turtles during their pelagic stage; these materials could be toxic. 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) and the coastal zone (juveniles, subadults, and breeders). The first set of conservation mea- sures pertains to activities on the nesting beaches and to supplementing reproduction; the second, to activities in the coastal zone off the coastal beaches and in the bays, rivers, and estuaries. Eggs, Hatchlings, and Nesting Females Nesting Habitat Critical nesting habitat can be protected through various types of public and private ownership and regulation of beach activities. Increased pro- tection can prevent damage from beach armoring, beach nourishment, and human use, including vehicular traffic. Relocation of nests can also help, but must be done by qualified and approved groups. The disorien- tation caused by artificial lighting might be reduced with the use of low- pressure sodium lights. Some municipalities in Florida have passed light- ing ordinances. Protection of eggs from predators and predator control on some beaches are important conservation measures. Kemp's ridley eggs at Rancho Nuevo still must be removed from the nests and protected from human and coyote predation to ensure their survival; almost all eggs are transferred to an enclosed beach hatchery and thus protected from predation. Headstarting Headstarting is an attempt to reduce the mortality of hatchlings by rear- ing them in captivity to a size at which their mortality rate in the wild should be lower. It is an active experiment with the Kemp's ridley, but headstarting has not yet proved to be effective. Benefits are uncertain, because some headstarted turtles appear to behave abnormally in the wild, many are soon caught in various fisheries, and none has yet been
10 Decline of the Sea Turtles recorded as reaching maturity or nesting. Headstarting methods have improved greatly, and proponents argue that the experiment has not yet received a fair test. The program has research and public-awareness ben- efits. Regardless, headstarting cannot be effective without concurrent reduction in the mortality of juveniles in the coastal zone. Captive Breeding Loggerheads, green turtles, and Kemp's ridleys have been raised in captivity from eggs to adults. The same species lay fertile eggs in captivi- ty. However, despite successes in captive breeding programs, the com- mittee does not consider captive breeding to be a preferred management tool. If a species became extinct except for captive animals, it would probably not be feasible to re-establish the wild population from captive animals, because captive animals in an aquarium or zoo would retain only a portion of the genetic material of their species. Artificial Imprinting Some limited evidence suggests that hatchlings might imprint on their natal beaches. The extent to which artificial imprinting might promote new nesting sites or restore old ones remains uncertain. Juveniles, Subadulls, ant! Breeders Conservation measures applicable to juveniles, subadults, and breeders involve the reduction of intentional harvest, reduction of unintentional capture and deaths in fishing gear, and modification of dredging opera- tions, oil-rig removal, and various other sources of human-associated mor tality. Prohibition of Intentional Harvest Intentional harvest of sea turtles in U.S. waters is prohibited by the Endangered Species Act. The increase in numbers of green turtles nesting at one site in southern Florida might be early evidence that prohibition has been effective. Similar protection has been implemented in Mexico, but enforcement is imperfect. 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 fin- fish fisheries can be reduced by limiting fishing effort at some times and places, closing a fishery, modifying fishing gear to exclude turtles or, for
11 Executive Summary trawl fisheries, reducing the tow times. New technology, such as the use of turtle excluder devices (TEDs) 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. There might be some areas and seasons in which turtles are so common that a fishery should be closed and other areas and seasons in which turtles are so uncommon that fishing could occur without the need for devices or procedures to reduce turtle mortali- ty. One area to consider for less stringent measures to prevent turtle deaths is the deeper waters of the Gulf of Mexico. Distribution data should be examined in detail to locate possible sites on fine spatial and temporal scales, for example by month, fishing zone, and depth. Turtle excluder devices are designed for installation in shrimp-trawling gear to release turtles from the net without releasing shrimp. By November 1989, six TED designs had been shown to exclude 97% of the sea turtles that would have been caught in nets without TEDs. They have been certi- fied by the National Marine Fisheries Service to exclude turtles. Some, such as the Georgia jumper, have stiff frames; others, such as the Morrison soft TED, are made only of soft webbing. The various designs differ in their ability to retain shrimp. Under good conditions, some designs have not been shown to reduce shrimp catch, whereas others have. A TED's perfor- mance also is affected by the roughness of the bottom and the amount of debris or vegetation on the bottom. Debris can collect on a TED and degrade the efficiency of the TED in excluding turtles and the efficiency of the net in capturing shrimp. Reduction of tow time might be a preferable alternative to the use of TEDs in some locations if there is too much debris. In some situations, a TED can improve the efficiency of trawling by excluding cannonball jellyfish, which otherwise would clog the net. Fishing effectively with TEDs requires some skill in adapting to local situations, but overall it is an effective way to protect the juveniles and adults that are important to the maintenance and recovery of sea turtle populations. TED technology transfer is crucial, because TEDs are effec- tive in excluding turtles from shrimp trawls. The National Marine Fish- eries Service has relied heavily on the Sea Grant program to help in the transfer of TED technology to shrimp fleets. Many activities have been undertaken, such as workshops, hearings, dockside and on-board demon- strations, presentations at industry meetings, and distribution of a large variety of written information. But the responses of commercial shrimpers to these initiatives have been poor in many areas. Making tow times shorter than those which kill turtles might work in some situations in which short tow times are feasible. If tow times are
12 Decline of the Sea Turtles limited to 40 minutes in the summer and 60 minutes in the winter, few, if any, captured turtles die or become comatose. Comatose turtles should be counted as dead, until effective rehabilitation techniques for comatose turtles can be developed and demonstrated. Limiting tow time is proba- bly more feasible with small boats in shallow waters. Even so, the prob- lem of multiple successive recaptures must be solved. Dreciging With respect to dredging, conservation measures might have included relocation, but in trials, some turtles have returned to the dredging area after an unacceptably short time. Several actions have been initiated: putting observers on dredges, comparing different dredge designs, redesigning deflectors, and studying the behavior and distribution of sea turtles in key navigation channels. Studies of the latter type in the Port Canaveral Entrance Channel have led to restricting dredging to the fall, when turtles are least abundant there. Collisions with Boats Collisions of boats with turtles are difficult to count, and conservation measures are inherently difficult to implement. Better evaluation of the extent of the problem could lead to production and distribution of educa- tional material and some boating rules in inside waters with high concen- trations of turtles. Oi~-Rig Removal The impact of oil-rig removal on sea turtles is poorly documented. Conservation measures should include surveys and removal of sea turtles before oil-rig demolition and further evaluation of the extent of the prob- lem. Power Plants A few sea turtles are still being entrained at the intake pipes of some power plants. 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. The International Convention for the Prevention of Pollution from Ships (known as MARPOL) makes it illegal to dispose of any plastics at sea. It also sets down guidelines to prohibit dumping of garbage (of the galley type) in nearshore waters. The consequences for
13 Executive Summary sea turtles of ingesting plastics and debris are poorly understood, and the subject needs further study. Eclucation Public education is important for calling attention to sea turtle conser- vation and implementing the conservation measures. Good beach man- agement stems from an informed and educated public. Many published materials are already available, and others will be needed, especially on the effects of fisheries on the sea turtle life stages with the highest repro- ductive value and on the effects of ingesting plastics and other debris. Resec rch Research projects on sea turtles have been many and varied, and they span such broad categories as distribution, population trends, food habits, growth and physiology, and major threats to survival. The com- mittee recognizes the need to improve the data bases for each of those categories, to establish long-term surveys of sea turtle populations at sea and on land, and to initiate experimental programs to increase popula- tion sizes. CONCLUSIONS AND RECOMMENDATIONS Conclusions 1. Combined annual counts of nests and nesting females indicate that nesting sea turtles continue to experience population declines in most of the United States. Declines of Kemp's ridleys on the nesting beach in Mexico and of loggerheads on South Carolina and Georgia nesting beaches are especially clear. 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. 3. Sea turtles can be killed by several human activities, including the effects of beach manipulations on eggs and hatchlings and several phenomena that affect juveniles and adults at sea: collisions with boats, entrapment in fishing nets and other gear, dredging, oil-rig removal, power plant entrainment, ingestion of plastics and toxic sub- stances, and incidental capture in shrimp trawls. 4. The incidental capture of sea turtles in shrimp trawls was identified by this committee as the major cause of mortality associated with human
14 Decline of the Sea Turtles activities; it kills more sea turtles than all other human activities com- bined. 5. Shrimping can be compatible with the conservation of sea turtles if adequate controls are placed on trawling activities, especially the mandatory use of turtle excluder devices (TEDs) at most places at most times of the year. 6. The increased use of conservation measures on a worldwide basis would help to conserve sea turtles. Recommendations 1. Trawl-related mortality must be reduced to conserve sea turtle popula- tions, especially loggerheads and Kemp's ridleys. The best method currently available (short of preventing trawling) is the use of TEDs. Therefore, although the waters off northern Florida, Georgia, South Carolina, Louisiana, Mississippi, Alabama, and Texas are most critical, the committee recommends the use of TEDs in bottom 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 TEDs might be ineffective (e.g., where there is a great deal of debris), alternative con- servation measures for shrimp trawling might include tow-time regula- tions under very specific controls, and area and time closures, as dis- cussed in Chapter 7. 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 histor- ically have been rare. 2. Conservation and recovery measures for all sea turtle species that occur in U.S. territorial waters should include protection of nesting habitats, eggs, and animals of all sizes. Of special concern are the nesting beaches of Kemp's ridleys in Mexico and of loggerheads between Mel- bourne Beach and Hutchinson Island in Florida. 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 protected. Lands are available for pur- chase, and action should be taken now. 3. Incidental deaths associated with other human activities such as other fisheries and abandoned fishing gear, dredging, and oil-rig re- moval" should also be addressed and reduced. 4. Headstarting should be maintained as a research tool, but it cannot substitute for other essential conservation measures. 5. Research on sea turtles should include improvement of the data base
15 E'cecutive Summary on survivorship, fecundity, mortality at all life stages; distribution and movements; effects of ingesting plastics and petroleum particles; para- sitism and disease, and other pathological conditions; and physiology of sea turtles, especially their resistance to prolonged submergence and their recovery from a comatose condition. Carefully designed and implemented long-term surveys of sea turtle populations both on land and in the sea will be crucial to their survival. 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. 6. Efforts to improve TED technology and explore other methods to con- serve sea turtles should be continued, including research on the effect tiveness of regulations.