Dr. J. Frazier:

5.96. Recent reviews of the topic of anthropogenic threats are provided by Eckert (1995) and Lutcavage et. al., (1997). For several of the countries involved, there simply are no (or very little) systematic data.

India: Kar and Bhaskar (1982) reported the consumption of turtles and eggs in most coastal states and Union Territories. In the south of Tamil Nadu and West Bengal there is a long history of direct exploitation of turtles (Frazier, 1980; Kar and Bhaskar, 1982; Silas et al., 1983b; 1983c; 1985; Pandav et. al., 1997); although illegal, these activities persist in the Bay of Bengal (Pandav et. al., 1997). For over a decade incidental capture and drowning in fishing gear has been known to be an important source of mortality of adult turtles, particularly in the Bay of Bengal; and trawlers, specifically shrimp trawlers, in Tamil Nadu, Andhra Praesh, Orissa and West Bengal have consistently been singled out for impacts that they cause (e.g., Kar and Bhaskar, 1982: 367, 368; Silas et. al., 1983a; 1983b; 1983c; 1985; James et. al., 1989; 1991; Dash and Kar, 1990; Mohanty-Hejmadi and Sahoo, 1994; Department of Fisheries et. al., 1996). Sand mining from beaches and coastal development have also been identified as threats for over a decade (Kar and Bhaskar, 1982).

Recent reviews identify development along the beach front (roads, buildings, tourist resorts), development of capital-intensive fishing operations (jetties and fish processing centers) and military installations, casuarina (Australian pine) plantations (which often make nesting impossible because of the dense cover of trunks and needles), incidental capture in fishing gear (notably trawl nets) and artificial lighting (Behera, 1997a; Pandav et. al., 1997; Choudhury, in press). With a long tradition of an active civilian population and free speech, there have been countless articles in the popular press, as well as initiatives from NGOs, focused on these various anthropogenic threats to sea turtles - particularly the problems of incidental capture in mechanized fishing boats, viz. trawlers and gill netters (e.g., Anon, 1982; Wright, 1984; Anon; 1985; Anon, 1986; Anon, 1992; West, 1995; Anon, 1996; Anon, 1997a; 1997b; 1997c; 1997d; 1997e; 1997f; 1997g; 1997h; 1997i; 1997j; Behera, 1997b; 1997c; Mishra, 1997; Panda, 1997, Rai, 1997; Sridhar, 1997a; 1997b).

Malaysia: Intensive, long-term egg harvest has occurred up until recently at most nesting beaches on both East and West Malaysia, and has been clearly identified as having been a major threat (de Silva, 1982; Siow and Moll, 1982; Mortimer, 1990; Chan, 1991; Eckert, 1993; Limpus, 1994; 1995; Chan and Liew, 1996a; 1996b). Hunting of turtles, namely in Sabah, has also been identified (de Silva, 1982; Eckert, 1993). Coastal development and habitat loss have been pointed out for some time (Siow and Moll, 1982; Leh, 1989; Mortimer, 1990; Chan, 1991; Chan and Liew, 1996a); this involves both terrestrial and marine environments, for example light and oil contamination at sea (Eckert, 1993; Chan and Liew, 1996a). Incidental capture in fishing gear, including drift/gill nets, long lines, traps, trawls (especially prawn trawls) and other gear (as well as dynamiting in Sabah) has also been identified for years (de Silva, 1982; Siow and Moll, 1982; Chan et al., 1988; Leh, 1989; Mortimer, 1990; Chan, 1991; Eckert, 1993; Chan and Liew, 1996a; 1996b; Suliansa et. al., 1996). Improper hatchery practices have also been singled out (Chan, 1991; Chan and Liew, 1996a).

The most recent review of Malaysian sea turtles (Liew, in press) lists several threats including: direct harvesting for tortoise-shell and leather, over-harvesting eggs, poaching, inadequate hatchery techniques, incidental captures in fishing gear and coastal and offshore development for tourism and industrialization.

Pakistan: At Hawksbay, Karachi, there have long been problems with development of weekend houses, which usurp nesting habitat along the beach. In addition, adult turtles have been washing up dead for decades. Kabraji and Firdous (1984) reported stranded turtles, especially during the monsoon. They had no direct evidence of cause of death, but proposed shark attack, as well as "Drowning in fishermen�s nets as part of incidental catch, Poisoning by pollutants such as oil, Disease". Firdous (1989) reported that 69 dead turtles were counted on the beach between June 1983 and June 1989. Most of the strandings were documented in the month of June, when tides and waves were the highest; 65 of the specimens were green turtles. There have been no systematic studies of this problem, but the evidence matches trawl-related strandings in other parts of the world. More recently, commercial trade, poaching of eggs, accidental capture in fishing nets, extensive shore-line development, disturbance and pollution have all been identified as threats (Asrar, 1995?).

The little information available from Baluchistan indicates that direct exploitation has been a serious source of mortality, but there seems to be no recent information. Groombridge et. al., (1988) reported commercial exploitation (thought to be green turtles) from remote beaches in Baluchistan. The levels of harvesting were claimed to be many thousands of turtles (mainly breeders) in a year; a short-term exportation to Japan was evidently involved, but there was also evidence that much of the exploitation was for local consumption. This all occurred in contravention of provincial legislation. As the area is remote, and much of the exploitation yield products is not recorded in normal statistics, it is next to impossible to know what happened historically or even what has happened in recent years. Groombridge (1989), later reported that "incidental catch appears to be a problem in surrounding waters." He suggested that the nesting colony in the Sonmiani region of Las Bela may have been extirpated by heavy exploitation.

Thailand: Harvest of eggs of most (all) species is known to be have been intensive for many years (Lekagul and Damman, 1977; Gilbert, 1981; Phasuk, 1982; Polunin and Nuitja, 1982; Hill, 1992; Eckert, 1993; Stuart and Cartin, 1994; Limpus, 1995; Settle, 1995). The same is true with the harvest of turtles of most (all) species (Lekagul and Damman, 1977; Gilbert, 1981; Phasuk, 1982; Eckert, 1993; Limpus, 1995; Settle, 1995). Coastal development and loss of nesting and feeding habitat is another widespread threat (Lekagul and Damman, 1977; Gilbert, 1981; Polunin and Nuitja, 1982; Settle, 1995). Incidental capture in fishing gear, including drift nets, purse seines, push seines, and notably trawlers, as well as cyanide and bombing, has been identified as a major threat (Lekagul and Damman, 1977; Gilbert, 1981; Phasuk, 1982; Polunin and Nuitja, 1982; Hill, 1992; Eckert, 1993; Stuart and Cartin, 1994; Settle, 1995). Inadequate management, notably headstarting and hatcheries, is also a problem (Stuart and Cartin, 1994; Settle, 1995 (see Donnelly, 1994; Mortimer, 1995; Crouse, 1996; Heppell et al., 1996a)). There have been notices in the popular press about turtles being caught and killed by trawlers (Matchima, 1996; Walakkamon, 1996). The most recent review of the status of marine turtles in Thailand identifies commercial exploitation of sea turtles and their eggs, coastal development, heavy fishing activities (trawling, gill nets, and long lines) (Supot, in press).

United States: Intense, direct exploitation of turtles, especially greens, in the continental United States ended in the mid 1970's, after decimation of these populations (Witzell, 1994), but evidently continues in many of the island territories of the Pacific (Eckert, 1993). A recent detailed analysis of anthropogenic threats for the Gulf of Mexico and Atlantic concluded that by far the most important source of mortality was incidental capture in shrimp trawls (National Research Council, 1990). Other threats include beach erosion, beach armouring, beach nourishment, beach cleaning and utilization, artificial lighting, gill nets, pound nets, fish trawls, traps, long lines, and a variety of other fishing gear, dredging actives, boat collisions, use of explosives underwater, ingestion of plastics and other contaminants (Lutcavage et. al., 1997). Oceanic drift nets and debris are of major concern, notably in the Pacific (Balazs, 1982; 1985; Balazs and Wetherall, 1991; Laist, 1995). The high incidence of fibropapilloma tumors - notably in Florida and Hawaii, and the devastating impacts on sea turtles has become a major concern, and there are suspicions that marine contamination is involved (George, 1997).

5.97. Without a doubt, reproductive and near-reproductive animals are most critical to the maintenance of a population. As sea turtles spend the vast majority of their lives in the sea, they are more subject to threats at sea in terms of the time spent at sea; these threats can be direct harvest (e.g., in nets), incidental capture (e.g., in fishing gear) or effects of contamination and marine pollution. However, while sea turtles are at their nesting grounds, they are concentrated in time and space, and generally this attracts concentrations of predators and exploiters. Hence, in general, they are more liable to predation while at their nesting grounds. However, the importance of a threat depends not on where mortality occurs, but how that mortality affects the population. As explained above, a few hundred eggs and hatchlings are less important to a population than is one breeding adult.

5.98. Different sources of mortality produce the same effects on the same stages of the life cycle: killing a reproductively mature turtle at sea for its meat, killing it as it comes to a nesting beach to lay eggs, or drowning it in a shrimp trawl means the same thing to the population - the removal of a breeding animal. In terms of the dynamics of the population, it really does not matter what killed the turtle, but rather how many were killed.

5.99. What is important is the life stage where the mortality occurs. One female may lay several clutches, each more than 100 eggs, and this she may do several times during one nesting season; and she can potentially nest for a period of decades. Thus, taking every single egg that she lays over a period of two nesting seasons, say, 1,000 eggs, means stopping her reproduction for two nesting seasons, but not completely. She has the potential (if she is not killed by any one of a variety of threats, both human and non-human) to return to the nesting beach on subsequent seasons and lay more eggs. If she can avoid mortality, she might successfully nest during 10 to 20 nesting seasons, each time laying perhaps 500 eggs. In this case, a female that lost 1,000 eggs in her first two nesting seasons, could successfully lay 5,000 to 10,000 eggs. What is critical, is that the turtle be able to survive to continue reproducing.

5.100. Fishing operations cause mortality - albeit incidental - which impacts large turtles, including those that are breeders and close to breeding. Shrimp trawling is one such fishing operation, which causes incidental mortality on large sized turtles (those that live in coastal waters). The special concern with shrimp trawling stems from several points. Because shrimp are generally most concentrated in coastal waters, trawling tends to concentrate in coastal waters (this occurs routinely, despite regulations and bans on trawling in these waters). Around the world, shrimp trawl fleets have grown faster than the shrimp stocks can sustain levels of exploitation, so the activity is regularly overcapitalized, and investments find decreasing returns. Shrimp trawling is targeted as a valuable export product, for which there is generally intense competition. Hence, shrimp trawling generally is carried out with considerable intensity, resulting in large areas of the benthos having the trawl pulled across them repeatedly. (One clear exception to the above paradigm is Australia, where shrimp fishery is closed entry (Tucker et. al., 1997), so the intensity of fishing effort has not spiraled out of control, as is the case for nearly every other fishing ground in the world.)

5.101. Where shrimp trawling is intense, and concentrated in coastal waters, there is a high probability that sea turtles will be caught and accidentally drowned. If these fishing activities occur near to breeding grounds (nesting beaches or mating areas) or in the migratory routes used by turtles to get to and from the breeding areas, or in feeding grounds, there is an extremely high probability that large numbers of turtles will be caught and drown. Where this happens, the numbers of turtles that are breeders and near-breeders killed incidentally can be relatively large. If this sort of operation continues, it can decimate a healthy population, make it impossible for a recovering population to recover, or even finally exterminate a population.

5.102. In terms of the general demographic phenomena, described above, the situation is similar in different parts of the world. However, each sea turtle population may have specific sources and intensities of mortality, at different times in the life cycle, which may occur at different places in the geographic distribution of the individuals, as they pass through different stages of the life cycle. Put another way, a dead turtle in Louisiana is just as dead as a dead turtle in Sabah.

5.103. Different stocks are under different situations, and different species have variations in the details of their life history. As such, each one may be affected somewhat differently by different types of mortality. For example, species that mature faster than others (ridleys for example) should be able to sustain relatively more mortality in the breeding adults, than species that require more time to mature. Nonetheless, there will be certain constants: increased mortality of reproductive, or near reproductive animals, will have more affect on the population than the same level of mortality on eggs or newly hatched turtles.

Mr. M. Guinea:

5.104. Threats to sea turtles have been compiled for the various countries. Few have ranked the order of the perceived threats. The ranking is as indicated in the references listed. It is unclear if the authors would give their consent to such ranking given the nature of the question.

5.105. The United States lists (Lutcavage et al., 1997): (i) beach modification by armouring etc.; (ii) Boat strikes; (iii) dredging and explosive platform removal; (iv) depredation of nests by animals; (v) pollution: oil, plastics and debris; (vi) incidental capture in fishing gear particularly shrimp trawls.

5.106. Thailand lists (Monanunsap, 1997): (i) the overuse of marine turtles and their eggs as sea food in the past; (ii) the sale of marine turtle products to tourists and for international trade; (iii) the deterioration of nesting habitats and marine pollution (light and plastics); (iv) the incidental capture of marine turtles in commercial fishing operations offshore.

5.107. Pakistan Lists (WWF, Marine Turtles of Pakistan): (i) Commercial trade for turtle skin, shell medicines and cosmetics; (ii) destruction of eggs by predators and poachers; (iii) accidental capture of turtles in fishing nets; (iv) extensive shore-line development, human disturbance and pollution.

5.108. Malaysia lists (Threats to Sea Turtles, http://www.upmt.edu.my/seatru/cons2.htm): (i) beach front development; (ii) heavy egg exploitation; (iii) incidental capture in set nets, drift nets, trawls and longlines; (iv) pollution (both light and industrial).

5.109. India lists (IUCN, 1995): (i) direct mortality: intentional catch by local and artisanal fisheries and on commercial long-lines; (ii) indirect mortality: unintentional catch causing drowning in trawls and gill nets; (iii) habitat degradation: beach destruction due to human activities, sand mining. Walking and driving litter and surface obstructions, disturbance by residential and commercial lights. Coastline modification due to construction etc. Beach destruction due to coastal erosion. Feeding, resting and developmental habitat destruction due to pollution and development; (iv) pollution: plastics and debris in the sea cause entanglement and drowning and death following ingestion; (v) boat collision; (vi) hatcheries: poor management of egg hatcheries; (vii) lack of information on sea turtle population sizes, migrations and natural and anthropogenic mortality levels hampers effective planning.

5.110. Human threats to sea turtles depend on the intensity and duration of the impacting activity. It is difficult to generalize between ocean and shore based threats. However, once the nesting beach has been lost the breeding unit has lost a critical habitat. As long as the nesting beach is intact there is a chance for seriously depleted populations to recover, should they be given enough protection.

5.111. Once eggs and adults are targeted as a commercial commodity, the breeding unit can suffer serious and rapid decline. Essentially, sea turtles are easy to capture and their eggs are easy to locate. Incidental capture is a relative modern term. Before the 1960's sea turtles were actively harvested in most countries in which they occurred. Modern fishing practices through effective management, should have little impact on sea turtles. This is embedded into the ethos of responsible fishing.

5.112. The species most at risk from shrimp trawling in the United States are the benthic feeding loggerhead, Kemp's ridley and to some extent the green (Robins, 1995). In Australia, flatback, olive ridley and loggerhead are the species most commonly caught in shrimp trawls of the Northern Prawn Fishery (Poiner et. al., 1995). However in the Queensland Trawl fishery, the order changes to loggerheads, greens, and flatbacks, olive ridley and hawksbills (Robins, 1995). The differences may be attributable to the species present in the different trawl fields and composition of habitats and depths on each of the trawl fields. Green turtles will be caught if the trawl field contains seagrass or abundant growths of algae. Hawksbills will be more commonly encountered amongst soft corals and algae. Leatherbacks are seldom caught in shrimp trawls.

Mr. H.-C. Liew:

5.113. The major anthropogenic threats to sea turtles are:

(a) Sea turtles are hunted for their meat and other products. Even though sea turtles are endangered and various countries have regulations to protect them, the hunting of adults and juveniles is still rampant. Some countries still permit such activities by imposing quotas but the quota numbers are in the thousands per year, often far exceeding what is sustainable considering the other threats facing sea turtles today. Very often, the numbers hunted illegally are estimated to be 2 to 5 times higher than the legal quota. Enforcement is generally very poor and difficult. All countries party to the dispute have banned such activities but their neighbouring countries like Costa Rica and Indonesia still condone hunting which invariably affect their population of sea turtles also.

(b) Incidental catch in fishing gears, e.g. shrimp trawlers, high seas gill-nets and other fishing gears. The impact of shrimp trawling on sea turtles appears to be the most important factor today threatening sea turtles in the United States. Thousands of olive-ridleys are also killed in Orissa, India, each year which conservationists attributed largely to shrimp trawlers. Incidental captures of sea turtles in shrimp and fish trawlers are also known to occur in Malaysia and Thailand; however, there is insufficient studies conducted to survey the extent of such impacts. Numerous other fishing gears are also known to kill turtles in Malaysia (Suliansa et al., in press), which, in some locations, appear more important than shrimp trawlers.

(c) A fair amount of turtles are killed or drowned in man-made structures (e.g., oil-rigs) or by speedboats and other powered watercrafts. Many of these go unreported except for stranding of dead turtles with lacerations on them. However, the number of turtles that do get stranded and reported is only a small portion of the true situation. Such problems occur in all countries with turtles.

(d) No estimates are available on the mortality caused by marine pollution to hatchlings, juveniles and adults. There are numerous reports of plastic debris in the stomach of autopsied stranded sea turtles, especially leatherbacks. Large numbers of hatchlings are probably killed or weakened due to the accidental feeding on marine debris like tar balls, styrofoam beads, plastics, etc. This is because hatchlings aggregate at oceanic drift lines where floating seaweed and other food items are found. Unfortunately, these are the same locations marine debris accumulate. Due to the scarcity of food items in the ocean surface, hatchlings would often attempt to feed on any small items that drift by.

(e) Mortality caused by diseases that may be anthropogenically induced, e.g., fibriopapillomas, is recent but spreading fast. It has affected several populations in the world from the Caribbean to the Indo-Pacific. Among the severe cases are the turtle populations in Hawaii.

(f) Trawlers, fish bombing, pollution, land reclamation and development are continuously destroying the feeding grounds of sea turtles. Large areas of sea-grass beds and coral reefs have been damaged or lost by these activities. All the countries concerned face these problems.

(g) Similarly, nesting beaches of sea turtles also face severe threats from beach front development, coastal protection structures like seawalls, land reclamation, sand mining, etc.

(h) Losses due to unsuitable or poorly managed hatchery practices also occur. Some of these losses can be very significant especially if hatcheries are the primary conservation effort practiced in those countries. Some Asian countries still practice the wrong conservation strategy of withholding newly emerged hatchlings for many days, or months to "harden" them before release, often termed as "headstarting".

(i) Commercial exploitation of eggs both legal and illegal is also still rampant especially in the poorer and developing nations like in some parts of Malaysia, Indonesia, Thailand, India, Maldives, Australia, Latin American nations and many others (Limpus, 1997)

5.114. The relative impact on sea turtle populations through egg harvests and direct harvesting of sea turtles vs. incidental capture of sea turtles in fishing operations, in particular shrimp trawling varies in different parts of the world. As mentioned earlier, egg harvesting and turtle hunting are well controlled in the United States, hence do not pose a major problem. Incidental capture in fishing operations, therefore, stands out as a major threat due to the large number of modern and efficient shrimping fleets, supported by the high demand for shrimps in the United States. The same cannot be said for developing countries in Asia. Even though these countries do have turtle conservation programmes, are signatories to CITES, and have laws to protect turtles, the level of enforcement can be quite different. Some of these countries even allow varied levels of commercial egg harvest or even killing of turtles for meat. Moreover, these countries do not have good statistics on turtle mortalities caused by fishing or shrimp trawling but records are available for commercial egg and turtle harvests where legal. Yet, many may go unreported. Thus, their reports would show egg harvest or turtle harvest as major causes.

5.115. The relative importance of threats does vary from species to species. For example, hawksbill turtles are hunted for their shell, hence largely decimated because of this activity. Leatherback turtles are largely pelagic, not known to rest on the seabed and feed primarily on jellyfish. Hence, threats caused by high seas drift nets and discarded plastic bags may be more important compared to shrimp trawling. Loggerhead turtles, Kemps ridleys and olive ridleys feed on crustaceans and shellfish found on the seabed, often in the same areas where shrimps are found, hence are most susceptible to being caught in shrimp trawlers. Green turtles forage primarily over seagrass and algal beds. Fishing and boating activities, and pollution in these shallow areas become more of a threat. However, for all these species of turtles, they are also vulnerable in the waters off their nesting grounds during the nesting season where they aggregate in numbers depending on the size of the nesting population. If some form of protection is accorded to these coastal areas during the nesting season, they may help reduce the threat caused by fishing.

Dr. I. Poiner:

5.116. I am only qualified to comment on current threat to sea turtle populations in the United States, Malaysia and Thailand. It appears that all sea turtle populations of all species in the three countries are severely depleted, and/or subject to over-harvesting and/or excessive incidental mortality. Anthropogenic threats in the three countries are similar (see Table 1, paragraph 5.71) but their relative importance is different. Most notably the indigenous harvests of eggs and adults in South East Asia is an important source of mortality not present in the United States, especially since the same stock will be fished in several countries in South East Asia. For example, the Malaysian green turtle population in Sarawak which has declined >90 per cent in egg production since the 1930s and is still under threat despite Malaysian conservation measures. One reason for the lack of recovery is egg harvests and adult fishing in neighbouring Indonesia since they are likely to be the same stock (Limpus, 1997).

5.117. As stated above, apart from estimates of the incidental capture and mortality of sea turtles in shrimp trawl fisheries (United States and Australia), and estimates of mortalities from boat strike, oil pollution and explosive platform removal mortalities in the United States, many mortality factors are not well quantified. It is not possible to estimate the full range of impacts on a stock and this is needed to assess population stability and the relative importance of different anthropogenic threats at sea or on the nesting grounds. None of the mortality factors are well quantified for south east Asia sea turtle populations.

5.118. In the United States the incidental capture of sea turtles in shrimp nets was identified as the major source of anthropogenic mortality for loggerhead, Kemp's ridley and green turtles when compared to other known sources of mortality (Henwood and Stuntz, 1987). However, there is no quantitative data on the various mortality factors in Malaysia and Thailand to make this assessment. In Australia, shrimp trawling has been identified as an important but not a key source of mortality for the six species of turtles that occur in Australian waters (loggerhead, olive ridley, green turtle, leatherback and hawksbill). The assessment is based on robust estimates of the incidental capture of sea turtles in shrimp nets (Poiner and Harris, 1996; Robins, 1995; Anon, 1997) and a variety of numerical population models (dynamic stage-structured and stochastic simulation models) for green and loggerhead turtles developed to help design and evaluate conservation policy and management (Chaloupka and Musick, 1997). Furthermore, there is significant variation in the relative catch and mortality rates for the different sea turtle species both within and between Australian prawn trawl fisheries (Poiner and Harris, 1996; Robins, 1995).

1(d) Is it possible to differentiate between shrimp trawl and other fishing gear in terms of the threat they represent to marine turtles? Are there regional differences in this respect?

Dr. S. Eckert:

5.119. By far the most serious threat to sea turtle stocks living in coastal environments are trawl fisheries. Trawling is particularly serious in that there seems to be a cumulative effect of capture stress. As a trawl net approaches a turtle's response is to flee directly away from the net (Ogren et. al., 1977). Observers suggest that the "doors" which hold the nets open act as "blinders" and they keep the turtle from veering away. Thus, the turtles swim directly in advance of the net until they are exhausted and are overtaken (Ogren et. al., 1977). While most species of turtles are capable of long term submergence in excess of 1 hour (the notable exception to this is the leatherback who routinely only makes 12-15 minutes dives (Eckert et. al., 1996), the exhaustion and depletion of oxygen stores during "the chase" renders them highly susceptible to asphyxiation. Even if the turtle escapes it may be physiologically stressed and subsequent captures may kill the animal (Stabenau, 1991). Another problem for turtles in areas that are bottom trawled is that such fishing methods degrade the habitats many species of turtle rely on as foraging areas (Dayton et. al., 1995). If seagrases are present, such fisheries uproot the sea grass and destroy the area for green turtle foraging or habitat for mollusca and crustaceans relied upon by loggerhead or the ridley species. Further, the constant perturbation may reduce the quantity of prey species that neritic carnivores, such as loggerhead and ridley turtles, rely on for food.

5.120. A close second to trawl fisheries in terms of potential to harm sea turtle populations are gillnet fisheries. Gillnets are very effective at drowning turtles in large numbers. While high-seas driftnets are banned by international agreement (primarily due to the massive bycatch problems caused by this fishery), coastal gillnets are still in use in many places. This type of fishery has probably been the primary cause of the recent decline in the Pacific leatherback population (Eckert and Sarti, 1997). Unlike trawling, there is no known solution to the incidental turtle bycatch problem with gillnets.

5.121. Longline fisheries are not entirely as destructive to turtles as the previous fishery style; however, they do have a large bycatch of turtles, and it is the largest growing fishing method in the world. The reason it may not be quite as destructive is that the drowning rate (=acute mortality) is lower for this type of fishery. However, there is data suggesting that post release mortality is substantial. (Balazs and Pooley, 1994, Aguilar et. al., 1992, 1993, Dayton et. al., 1995). Purse seine fishing does catch turtles, but the mortality rate of such fisheries is negligible for turtles (S. Eckert, unpub data).

Dr. J. Frazier:

5.122. The characteristics of the gear - where, when and how it is used - will determine the organisms that are likely to be impacted by it. For example, gear that is used in coastal waters will affect the turtles when they are in coastal waters; gear that is used on the high seas will affect the turtles when they are in the open sea. Many types of modern fishing activities are known to have deleterious effects on a wide variety of marine organisms, including sea turtles. Modern fishing techniques, such as, drift nets, long lines and trawls are responsible for incidental catch and mortality. Because of its nature, bottom trawling is known to cause major impacts on non-target species because it is an unselective method of fishing (Norse, 1997a). Shrimp trawls are notoriously unselective, and on a world level it has been estimated that they are responsible for more than a third of all bycatch (Alverson et. al., 1994). Hence, shrimp trawls not only catch and drown turtles, but they are responsible for an extraordinary amount of bycatch and discards in world fisheries: it is estimated that approximately 10 million tons of bycatch result from shrimp trawling. This level of environmental perturbation carries with it many other risks, both ecologically and socially. In the end, any of these gear used where there is a likelihood of incidentally capturing turtles poses a threat to the animals, and when a population is at risk all of these sources of mortality must be drastically reduced.

5.123. Since individual marine turtles migrate and disperse over vast distances, they are vulnerable to incidental capture in many different regions. The environmental and social impacts of shrimp trawls are most acute in the tropics (Alverson et. al., 1994) where the intensity of trawling is high, bycatch ratios are high, human populations are high, human food needs are high, dependency on fish is high, proportion of trawled catch which is exported is high, and local availability to traditional fisheries resources is declining. For this reason, there have been calls, nationally and internationally, to ban this form of exploitation of common marine resources (O'Riordan, 1994; SAMUDRA, 1994).

Mr. M. Guinea:

5.124. Few quantitative data are available on the numbers of sea turtles caught in fish trawls, set nets (Chan et. al., 1987), long lines and driftnets (Eckert and Sarti, 1997). Sea turtle mortality in shrimp trawls increases with trawl duration (Poiner et. al., 1990). Short tows of less than 60 minutes pose little threat to sea turtles. Trawls lasting longer than 60 minutes have a proportionally greater influence on sea turtle mortality. Set nets may be set for any length of time. This depends on the target species. Nets set for shark products may be checked only once a day. Others may be set for several hours to coincide with a tidal stream. A single bottom-set, large-mesh, gill-net killed in excess of three hundred turtles in four days of netting in Northern Australia (Guinea and Chatto, 1992). This was approximately equal to the expected annual mortality of sea turtles in the entire Australian Northern Prawn (Shrimp) Fleet which trawls along more than 10,000 km of coastline each season (Poiner et. al., 1990).

5.125. There will be regional differences between shrimp trawl and other fishing gear in terms of the threat they represent to sea turtles depending on the species of sea turtle present and the nature of the nets being used (see paragraph 5.124).

Mr. H.-C. Liew:

5.126. Sea turtles are threatened by numerous fishing methods ranging from hook and lines, drift or gill nets, purse seines, trawlers, fish traps, fish bombing, etc. How much of a threat are they depends on whether the fishing activity occurs during the period and in regions where significant numbers of turtles occur, e.g. feeding and nesting grounds, migration routes. It also depends on whether the gear or methods cause severe injury or entangle the turtle, resulting in drowning. The differing habits of the different species during feeding, resting, swimming, etc, can also influence the threats by different gears. For example, leatherback turtles are known to feed primarily on jellyfish in the pelagic zone of deep oceans. They would be less likely to be caught by shrimp trawling but are more susceptible to high seas gill-nets and longlines.

Dr. I. Poiner:

5.127. Since there is no quantitative data on the mortality from other fishing gear on sea turtles, it is not possible to make this assessment. However, given the variation in the type and size of the different bottom trawl and other fisheries around the globe there is likely to be significant regional differences in this respect.

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