Human Sea Turtle Survival · or taken by predat~rs.""~ Loggerhead hatchlings can escape from a 3-cm-deep footprint, but are unable to escape a tire rut of similar depth. Hatchlings

15 Human Impacts on Sea Turtle Survival

Molly E . Lutcavage. Pamela Plotkin. Blair Witheringion. and Peter L . iu iz

CONTENTS

15.1 Introduction ................................................................................................. 388 ........................................................................ 1 5.2 Habitat Alteration and Loss 388

............................................................... 15.2.1 Nesting Beach Concerns 388 15.2.1 . 1 Beach Armoring ........................................................... 389

........................ 15.2.1.2 Beach Nourishment and Sand Mining 389 ............................ 15.2.1.3 Beach Cleaning and Beach Driving 390

.................................... 15.2.1.4 Human Presence on the Beach 390 15.2.1.5 Artificial Lighting ........................................................ 391

................................................................................... 15.2.2 Boat Strikes 392 .... 15.2.3 Dredging, Explosive Platform Removal, and Other Activities 392

.................................................. 15.2.4 Depradation of Sea Turtle Nests 392 ................................................................................................ 15.3 Oil Pollution 392

................................................................. 15.3.1 Oil Pollution Concerns 392 1 5.3.2 Laboratory Studies ........................................................................ 394

........................................................ 15.3.3 Oil Spill Response Activities 395 15.4 Other Pollution Sources and Entanglement ............................................... 395

......................................... 1 5.4.1 Plastics and Non biodegradable Debris 396 ........................................................................................ 15.4.2 Ingestion 396

.................................... 15.4.3 Physiological Effects of Debris Ingestion 397 15.4.4 Entanglement ................................................................................ 398

........................................ 15.4.5 Types of Debris and Sources of Origin 398 .................................................................. 15.5 Fishing and Incidental Capture 398

............................ 15.5.1 Shrimp Trawling and Turtle Excluder Devices 399 15.5.2 Pelagic Fishing Gear ..................................................................... 400

............................................................. 15.5.3 Coastal Fishing Activities 401 .......................... 15.5.4 Artisanal and Commercial Sea Turtle Fisheries 402

15.6 Conclusions ................................................................................................. 403 .............................................................................................................. References 404

15.1 INTRODUCTION

As detailed in the introductory chapter by Pritchard, .sea turtles have a long and ancient history. Sea turtles arose in the early Mesozoic. and for the next 100 million years. during the rise and reign of the dinosaurs, they shared the oceans with a rich diversity of other air-breathing marine reptiles. By the end of the Cretaceous era. the sea-going ichthyosaurs and plesiosaurs were extinct, but sea turtles tenaciously survived and indeed nourished up until very recent times. But today their numbers are drastically reduced to the point that all seven remaining sea turtle species are considered either threatened or endangered on a worldwide basis. Undoubtedly, human interference is the cause of this collapse. The challenges that sea turtles now face from human activities impact every stage of their life cycle, from loss of nesting beach and foraging habitats to mortalities on the high seas through intense pelagic fishing practices. They are also harmed by the increasing loads of nonbiodegradable waste and pollutants that the oceiins and coastal zones now receive.

Clearly. a full consideration of all human activities that adversely impact sea turtles and required conservation measures would be beyond the scope of a single chapter. However, a review of [he more compelling effects will give an indication of the extent of the challenges sea turtles face and the efforts required to protect them. A word of caution: by its very nature much of the data on this subject is only found in the "grey literature" of government and conservation organization reports and such like, and is therefore scientifically unreviewed. This is sometimes the case in conservation biology, where threats to survival are first recognized and conservation remedies proposed by biologists familiar with the status of local populations.

15.2 HABITAT ALTERATION A N D LOSS

The translocation of nests into hatcheries is probably the most comrnon sea turtle conservation technique undertaken when Ivuch operations threaffn SP;! turtles. These efforts are usually practiced where serious threats to embryos or hatchlings are thought to exist. High levels of egg poaching, predation, erosion, artificial lighting, beach nourishment projects, and vehicular and foot traffic have been cited as justi- fication for nest trmslocation. However. there are potential problems inherent in moving eggs and incubating them under artificial conditions, including increased egg mortality and reductions in genetic and realized fitness.

Translocated sea turtle nests can have lower hatching rates than undisturbed natural nests,'Â¥ although under certain conditions translocated nests may do better.' Additional problems with translocation arise from changes in the incubation environment. Differences in temperature, hydric environment, and gas exchange affect hatching rates and possibly the vigor and survivorship of hatchlings! During the initial years of the Kemp's ridley conservation program, low egg incubation temperatures resulted in the production of hatchlings that were primarily males.' This example shows that merely counting the number of mostly male hatchlings produced does not reveal the success of a tr~nslocaiion progriim. Important assessments for

conservation include hot11 number of hatchlings and their Iitncss - i.e.. likelihood of surviving. returning 1 0 an appropriate beach, and leaving offspring that themselves survive.

15.2.1.1 Beach Armoring

Beach armoring consists of hardened structures meant to protect dune property from erosion. This includes vertical or inclined concrete sea walls, wooden walls, rock revetments, and sandbadsandtube structures! From the perspective of a nesting turtle, armoring is detrimental if it is rigid enough to impede access to the nesting habitat. Even "soft" structures such as sand fences pose threats similar to harder. more permanent fortifications. Structures meant to control longshore sand movement such as groins and jetties also may present similar barriers to nesting turtles.

The greatest threat that armoring poses for sea turtles is to eliminate nesting h-abitat. An example of how this can occur can be found in the case of the barrier island nesting beach at Jupiter Island, FL. This partially developed island suffers a net erosion of sand largely due to the sand starvation effects of an inlet jetty. Whereas both developed and undeveloped stretches of Jupiter Island are losing sand from the beach, only the developed stretches have been armored. On the natural beach. dune sand has replaced eroded beach, but on armored stretches, waves wash up to the foot of walls and revetments, leaving no dry beach for nesting.

The problems caused by beach armoring will be greatest where coastal development is most widespread. This is especially the case in the U.S. and Mediterranean where coastal development is older and dune structures have had more time to become threatened by erosion. Elsewhere, the installment of armoring and its effects on sea turtle nesting will become an important conservation issue as sea level rises. beaches erode, and buildings are defended from the sea.

Whether sea turtles kept from nesting at armored beaches may forgo nesting altogether or move to adjacent suitable nesting beaches is unknown. Although a concentration of nesting effort at suitable nesting sites would allow reproduction to continue, an increase in density-dependent mortality of eggs and hatchlings would ensue.

15.2.1.2 Beach Nourishment and Sand Mining

Beach nourishment involves mechanically dumping or pumping sand onto an eroded beach. Because this is an expensive undertakine. these activities are primarily conducted on the beaches of developed countries (especially the U.S. and E u r w where the economic value of the beach makes such an effort worthwhile.

Beach nourishment is a preferred alternative to annoring. However, beach nourishment replaces rather than maintains the original nesting habitat. and the suitability of this renourished habitat for sea turtle nesting will depend on the quality of fill material and the methods used to deposit it. Some nourished beaches have a high clay, silt, and shell content that makes them too compact for nest excavation. Often on nourished beaches. wave action causes steep escarpments to form that prevent turtles from reaching the upper beach. Properties of an artificially nourished substrate

that differ from a natural beach include sorting. moisture content, reflection, and conduction. These properties affect the architecture of the egg chamber, incubation temperature, gas exchange, and water uptake for a developing clutch and result in diminished egg and hatchling survivorship.

In Florida. exhaustion of local sand sources for beach renourishment has stim- ulated the use of aragonite sand from the Bahamas. Incubation temperatures of clutches in the white aragonite sand are 1 to Z0C lower than for natural Florida silicate sands. a factor which may have an important effect on the hatchling sex ratios (see chapter by A~kerrnan).~

There are economic incentives to nourish beaches during the summer nesting season when costs are lower due to calmer seas. Renourishment projects during the nesting season are already taking place in Florida, with an environmental cost to sea turtles. Although large-scale transloeations of eggs to hatcheries precede these projects, an estimated 8% of the nests are missed by field workers and probably destroyed during beach nourishment activities. Translocation itself can cause egg mortality, and the process of nourishment involving lighting. sand spreading, and pumping activities could disturb nesting females, and produce disorientation and mortality in hatchlings.

In sand mining operations. large quantities of sand are dug from beaches to be used as fill. in production of concrete, and for other construction activities. Sand mining destroys the beach, eliminates nesting. and is recognized as a threat to some sea turtle populations. primarily in the Medite~anean." '~

15.2.1.3 Beach Cleaning and Beach Driving

Beach cleaning and beach driving involve vehicular traffic and its effects. Heavy vehicles can crush developing eggs and pre-emergent hatchlings, and the tire ruts resulting from traffic can "entrap" hatchlings. allowing them to become exhausted or taken by predat~rs .""~ Loggerhead hatchlings can escape from a 3-cm-deep footprint, but are unable to escape a tire rut of similar depth. Hatchlings may crawl along ruts due to their tendency for orientation toward open areas."Vehicles operated at night can disturb nesting females and crush emerging hatchlings crawling toward the sea.

The principal deleterious impact of beach cleaning on sea turtles is to uncover and destroy nests. waking can also leave ruts or ridges that disrupt hatchling sea- finding behavior. Beach cleaning can be regulated so that the effect on sea turtle nests is low.

15.2.1.4 Human Presence on the Beach

Although the effects of human foot traffic on sea turtle nests are largely unstudied, these perceived impacts are commonly used as a rationale for translocating nests. As with vehicular traffic, foot traffic has the potential to damage buried eggs and harm pre-emergent hatchlings. Human visitation at night can cause turtles to abort nesting attempts, although where visitation is controlled within guided "turtle watch" groups, this disturbance is minimal.'4"'h "Turtle watch" outings have an important

conservation anil educution potential und are hecoming u common form of eco- tourism. However, even well-intentioned eco-tourism programs can lead to unex- pected conflicts. For example, in Costa Rica, former subsistence turtle hunters and "hueveros", or egg collectors, have been trained as turtle guides, and now derive income by leading nesting beach tours. There is some indication that the strong economic incentive to attract a large number of tourists to some important nesting beaches may be at odds with the need to minimize disturbance to nesting females and emergent hatchlings. Fortunately, these problems can be addressed through educational programs and goal setting by the conservation and residential communities alike.

15.2.1.5 Artificial Lighting

Artificial lighting on nesting beaches is detrimental to sea turtles because it disrupts critical behaviors, including nest-site choice and the nocturnal sea-finding behavior of both hatchlings and nesting females. There is both associative and direct exper- imental evidence showing that artificial lighting on beaches deters sea turtles from nesting." Reduced nesting on lighted beaches appears to be the result of fewer attempts at emerging onto the beach rather than the abandoning of attempts after turtles emerge onto the beach. Nesting that does occur on or near lighted beaches can produce high hatchling mortality. Hatchlings move toward artificial light sources rather than the sea. and succumb to exhaustion, dehydration, and predation. 14~'9~21

Hatchling mortality from artificial lighting is difficult to detect and is generally underestimated. Effects of lighting vary with the lunar cycle and are greatest during the new moon period.22As a general rule, any artificial light source that is visible from the nesting beach may disorient sea turtles.

Many options exist for managing light near nesting beaches. Light sources can be minimized in number and wattage, shielded, redirected, lowered, recessed, or repositioned behind shielding objects so that light from the source does not reach the beach. Installation of timers and motion-detector switches will ensure that lighting is on only when needed. Interior lighting can be reduced by moving lamps away from windows, drawing blinds after dark, and tinting windows.

Light sources that emit comparatively low levels of short-wavelength (blue and green) light affect both hatchlings and nesting adults less than sources emitting higher levels of short-wavelength light.'n~23 For this reason, low-pressure sodium vapor luminaires (a monochromatic yellow source) make good substitutes for more disruptive lighting.24Yellow-tinted incandescent "bug light" bulbs are another appropriate substitute where lighting problems have been only partially solved by other means.

In the U.S.. Costa Rica. Greece, and Australia, there are conservation programs in place to educate beach visitors and residents about the harmful effect of lighting on sea turtles. In Florida and South Carolina, local power companies have distributed educational materials to coastal consumers. Presently, most Florida communities near nesting beaches have light-management ordinances designed to protect sea turtles.

Sea turtle stranding data for the U.S. Gulf of Mexico and Atlantic coasts, Puerto Rico. and the U.S. Virgin Islands show that between 1986 and 1993, about 9% of living and dead stranded sea turtles had propeller or other boat strike injuries (n = 16,1U2).1"-26 In Florida where coastal boating is popular, frequency of boat injuries between 1991 and 1993 was 18% of 2,156 strandings. Countless numbers of loggerheads and 5 to 50 Kemp's ridley turtles are estimated to be killed by vessel traffic per year in the U.S.?' Although some of these strikes may be post-mortem, the data show that vessel traffic i s an important cause of sea turtle mortality.

Dredge and till activities occur in many of the nearshore seasonal habitats of sea turtles worldwide. Operations range in scope from incidental propeller dredging by recreational boats to large-scale drcdging of channels and fill for land reclamation. Sea turtles have been killed by hopper dredging in Florida and Georgia, but the extent of mortality in other geographic regions is ~nknown.~"

Sea turtles associate with offshore oil and gas platforms, and can be harmed by underwater explosions detonated to remove platforms no longer in service.3 These explosions can cause capillary damage, disorientation, and loss of motor control in sea turtles. Although sea turtles far from explosion sites may suffer only disorientation, those near detonation sites will most likely sustain fatal injuries.3o Estimates of sea turtles killed from explosive platform removal in the Gulf of Mexico range from 50 to 500 per year.^7 Petroleum seismographic canons and military maneuvers involving explosives also have the potential to harm sea turtles, but specific information on their impacts i.s Jacki~g.?~

Companion animals and pests attracted to trash and food remains left by humans can have a devastating impact on the success rates of sea turtle nesting beaches.'? Nesting depredation by feral hogs, pigs, foxes, coyotes, coatis, mongooses, and dogs can destroy up to 100% of nests." Municipalities have taken steps to eliminate or reduce this disturbance with predator removal programs and the use of tamper-proof trash receptacles.

15.3 OIL POLLUTION

Sea turtle populations around the world coexist with oil and gas exploration, trans- portation, and development. The risk of this association is demonstrated in the growing record of turtles harmed by oil in the Gulf of Mexico?' the Atlan~ic,'~ the Caribbean Sea," the Gulf of iraq,34 the Mediterranean.j5 and the Red Sea.^ Indeed,

the extent of oil anil tar pollution in ocean surface WiitCrs i s entÃˆrmous The Surgasso Sea alone entraps an estimated 70,000 metric tons of tar."

Sea turtles are exposed to the harmful effects of oil pollution in many ways (Figure 15.1). By continuously resurfacing through an oil slick to breathe, adulln would experience prolonged physical contact with the floating oil. Ocean convergent zones and drift lines, where pelagic juveniles are found, are also regions where floating tar accumulates. The sea turtle's mode of respiration, a rapid inspiration of surface layer air before diving, would introduce petroleum vapor into the lungtt. Eating contaminated food or tar balls brings petroleum materials into the intestine. On nesting beaches, oil deposits could interfere with normal development of the embryos in the egg clutch as well as present a lethal hazard to newly emerged hatchlmgs. It is clear that all sea turtle species and life stages are vulnerable to the harmful effects of oil, through direct contact or by fouling of their habitat^?^,^'

SKIN -

Parasitism, Disease Ã‘Â Viability Ã‘Ã‘Ã‘Ã‘ PREDAm Decreased INCREASKt

Aerobic scope LUNG ' decreased Foraging time

\ /reduced \ Dive time ------- decreased - REDUCED

OIL : Assimilation --------- GUT ---- decreased 1 J ., Organ PERFORMANCE

^ - Internal affects Dysfunction DEPRESSED -.. \ Hormone .-Ã̂ R E P R O D M

Balance disturbed D E C W

SENSE Ã‘k Interference -- .- - - BEHAVIOR ORGANS PERTURBED

EGGS - -k> Abnormal Development ---Ã‘Ã‘Ã‘Ã‘Ã‘Ã‘Ã‘Ã‘ DEATH

FIGURE 15.1 Conceptual model of potential effects of prolonged oil exposure on W turtles. The primary impacts on organ systems, drawn from documented effects in laboratory studies, may work synergistically to produce behavioral changes, interference with sensory systems, reduced fitness, and eventual death. (From Lutz el a l . 9

There is direct evidence that sea turtles have been seriously harmed by oil spill8. A recent fuel oil spill oiled loggerhead nests and jeopardized hatchlings and adult females in Tampa Bay. FL. In 1979, the Mexican Ixtoc blowout oil breached Rancho Nuevo, the only known major nesting beach of the Ken~p's ritlley, and oiled sea turtles were subsequently seen in Texas coastal waters.-*" There is evidence that in 1983. 180 hawksbill turtles were killed by oil spilled off the islands of h a and Karan, near Saudi Arabia!' Although the documentation of the numbers of sea turtle8

killed by oil spilled during the Gulf of Iraq conflict is scanty, estimates range from tens to hundredsY2

On a yearly basis about 1% of strandings identified by the U.S. sea turtle stranding network are associated with oil, with higher rates in South Florida (3% of strandings) andTexas beaches (3 to 6.3% of st ran ding^)."'^'.^^ From 1980 to 1984, 37.5% of Dade County, FL sea turtle strandings were petroleum related, probably due to the heavy surface and beach tar occurrences reported in South Fl~rida.~'Rates may also be high in transport routes through the Caribbean and other areas. Oil removed from stranded sea turtles in Florida and Texas has been identified primarily as tanker washings from diverse sourcesY5 Pelagic size-class loggerheads, hawksbills, and green turtles are known to strand, having been mired in oil,32

In the western Atlantic and Gulf of Mexico offshore, sea turtle distribution has been linked to zones of convergence.1334 Convergence fronts and Langmuir cells concentrate zooplankton and other prey items, serving as dependable feeding zones for sea turtles, marine birds, and other pelagic foragers. Unfortunately, marine debris and oil also collect in these areas, which increases the probability of prolonged contact with oil. tar, and harmful d e b r i ~ . ~ " ' ~ In convergence fronts east of Florida, tar was found in the mouth, esophagus, or stomach of 65 out of 103 post-hatchling loggerheads."A loggerhead sea turtle sighted during a Gulf of Mexico aerial survey surfaced repeatedly within a surface oil slick for over an hour."

Dramatic as it is. direct evidence of the effects of oil on sea turtles must grossly underrepresent the problem. Oiling on the high seas and inaccessible beaches are not likely to be documented. Secondly, only a small percentage of the animals killed by oil would presumably strand, and of these, even fewer are likely to be found and recorded.

15.3.2 LABORATORY STUDIES

Although lethal effects of oil pollution on sea turtles have been demonstrated, e.g., hatchlings apparently starved to death as a result of their beaks and esophagus being blocked with tar balls, sublethal encounters are likely to be much more common. and may have a greater deleterious impact on sea turtle populations. Laboratory studies indicated that sea turtles will pursue and swallow tar balls indiscriminately and that they a p p a r to be unable to detect and avoid oil ~ l icks .4~

Despite the high tolerance of sea turtles to physical damage, they are surprisingly sensitive to oil. In laboratory studies on juvenile loggerhead turtles, almost all of the major physiological systems were adversely affected by short exposures to weathered South Louisiana crude ~ i l .~"~~Sign i f i can t changes in respiration, diving patterns, energy metabolism, and blood chemistry occurred following oiling. A three- to sixfold increase in white blood cell count suggested that a rapid immune response was initiated in oiled turtles. Hematocrit and hemoglobin concentration decreased slightly during oiling.These parameters are critical components of the oxygen transport system of the blood. Changes in metabolic indicators showed temporary interference with digestion. The salt glands, paired organs located in the eye orbits (see Chapter 13). failed to produce fluid several days after oil exposure, although function returned within two weeks."^Mechanical blockage of tear ducts or an inflammatory

response to the presence of oil may have inhibited salt gland function. Prt)longed salt gland failure could have serious if not fatal consequences, since it would interfere with water balance and ion regulation. Turtles also experienced acute contact der- matitis, or disruption of the architecture of the skin, mucous membranes, and sensory ~ r g a n s . ' ~ - " ~ ~ ~ A break in the skin barrier could act as a portal of entry for pathogenic organisms. leading to infection and debilitation.

Petroleum hydrocarbons were not detected in skin or blood samples from log" I I

gerhead sea turtles that were exposed to a weathered oil slick for no more than 96 h." However. there is some evidence of bioaccumulation in sea turtles exposed for longer periods. After the Gulf of Iraq war, a stranded green sea turtle had 4050 and 3 10 mg of oil per kilogram of tissue in its liver and stomach. respe~tively.4~ Externally the turtle did not appear to have been oiled, and until necropsy had been assumed to have died of natural c a u ~ e s . 4 ~

Kemp's ridley sea turtle embryos from eggs incubated in sand contaminated in situ by the Ixtoc blowout had survival rates similar to eggs incubated in unoiled sand.4"However. Ixtoc oil was highly weathered, and would have lacked most of its volatile components. In contrast, the number of viable eggs and hatchlings surviving to be released from nests incubated in the laboratory were significantly lower in nests contaminated by unweathered crude oil than that of control^.^ It should be emphasized that the laboratory studies only concerned the effects of weathered oil - prolonged contact with freshly spilled oil would undoubtedly be considerably more harmful. It stands to reason that the cumulative harmful effects of an oil spill can be catastrophic.

Oil-spill response activities have great potential to harm sea turtles if carried out without regard to sea turtle behavior. Beach cleaning operations involve artificial lighting and heavy machinery which may disturb the beach profile and disorient nesting sea turtles and hatchlings. Because of the timing of critical events during embryogenesis, sea turtle eggs can only be moved during specific periods of incubation. which limits relocation as a mitigation opt i~n.""~~ '

Booms used to contain oil may impede access, cause direct fouling or entanglc- ment, and increase predation risks to hatchlings. Increased vehicular and vessel traffic in shallow areas such as seagrass beds can adversely affect foraging habitat and cause displacement from preferred areas. Oil spill contingency plans for areas where sea turtles are found should have specific response procedures in place to protect sea turtles.

15.4 OTHER POLLUTION SOURCES A N D ENTANGLEMENT

Sea turtles can achieve life spans greater than 50 years, and have a potential 10 bioaccumulate heavy metals and pesticides. In the coastal zone. chronic pollution from industrial, agricultural wastes, and urban runoff is a threat to sea turtles.27'34-52'53 Unfortunately, there is little information about this problem. In Chesapeake Bay,

D c h r i s ingestion is not often d i rcr t ly in1plic:itrd i n turtlr 111onality. n:inlely I x - r . i i ~ ~ . ~ ~ only sni;ill tpi;itititirs o f (1'-hris wel l mixed w i th n;iiiir:il food ifems ;ire p - i i i ~ i . ~ I l ~ seen in tile i l i w i v e t r :~ r t . ' " " '~ Debris i n !lie i l i ~ i v e tr:ict i s coni i i innly seen (1111 111"

nt.".ropsi~.s" .mil i s c lc fL ' r :~~e~l hy l ive c : ip tnr~( l se;i t~ir t I i~s." '"~+~" I s the incrs i inn 1 1 1

Jel-iris. i n p;inicii!;ir pliistic ;in4 l:itr\. hy w tufllcs t h e r ~ ~ f n r c ;iny c;111se for C I ~ I ~ L ~ ~ - I I I ' C1e;irly. it' sut'ticient i i i : i~cri; i l i s w i l l o w e d to I~:IIISI> ;I i.on~pIrtt* s t o p p : ~ ~ ~ 01' tile i+111,

(ic;11ti w i l l result h m s~;~rv; i i ior~. This ;ippc;irs to he ;I rclntivcly rare WÃ .̂-11 111

i*{.11~111;irison \ v i t l i the frequency \vi l l i which smaller ;1n1011nts ;ire in~estc. '" ' l l ~ n v t ^ i-r,

i l ie siit~:it ion is much more ~ r r i o ~ ~ s i f Â¥ie; 111rt1cs lire Iviirnieil hy i n x s i i o n ot p l ; ~ \ i i i ~ ml l : ik~ :II 1111;1ntitic"' much s11i:illcr tti;in ttiosc ncci"'s:~r\' l o r yl s l r : ~ n ~ ~ l ; i t ~ i Ã ˆ n

CII~I~I~\ILY~ SIIIIIIVS ts lierv 111rtl~s \ w r c p r c ~ ~ n i c i l wilh sn1:lll : t t i i o ~ ~ ~ i t s o r t \ c * I ~ i I,-

i lCnioiistr;~tcd th:it when I i ~ i ~ i c r y . sc;i lurlltxs w i l l : ic t iv r l \ cons~in ic plastic ;IIII~ l : i t r t

materi;il. '" ' I The yioiim of [l ie ingested l;nc\ 111;11cri;il i n tlic yut ranye<! f rnm ;I t i ; \ \ cl;iys 1.1uir 1110nths. i n i l i c ; i t ~ ~ l r thl some of' tlie l;itcx pieces were I w i n ~ i e l i l 111' in

the intestine. Although little change in blood chemistry was noted following ingestion in these experiments, except for a fall in blood glucose levels, some tunics became positively buoyant.'"^'' In the wild, positive buoyancy would render afflicted individuals more susceptible to collisions with boats, increase the chance of incidental capture in some commercial fisheries, and increase predation riskJO Clearly, information is needed on the physiological effects of ingestion of larger quantities of plastics by sea turtles and the levels at which adverse impacts occur.27 It has also been suggested that ingested plastic could result in PCB a c c ~ m u l a t i o n . ~

Entanglement in derelict fishing gear is a serious problem for sea turtles. Entangle- ment may occur when sea turtles accidentally swim into the derelict fishing gear or when they are attracted to the accumulated epibionts encrusting old floating debris. Leatherbacks have been reported entangled in active crab and lobster traps and even whelk line^,^^'^^ and there are records of juvenile hawksbills trapped in plastic-woven sacks4 Entanglement can result in reduced mobility, making the turtle unable to feed or flee from predators. If forced to remain at the surface they may become more susceptible to collision with boats or incidental capture. Trailing debris may trap sea turtles between rocks or ledges, resulting in death from drowning, and constric- tion of the neck and flippers can amputate limbs and consequently lead to death from infection.

15.4.5 TYPES OF DEBRIS AND SOURCES OF ORIGIN

Much of the marine debris that entangles sea turtles originates from boats and ships and from offshore oil, gas, and chemical platforms. Some marine debris comes from land, entering the oceans via rivers and beaches. Plastics are the most abundant type of anthropogenic debris found on beaches and in the oceans." Plastics are also the most common type of debris sea turtles become entangled in and inge~t:'~ As the general use of plastics for industrial and commercial purposes increased over the last 40 years, so have the amounts and types of plastic appearing in the oceans.

Fishing gear. and in particular monofilament line, is one of the most commonly encountered anthropogenic debris that endangers sea turtles, and may account for 68% of all entanglement case^.^^'^' In addition to material commonly perceived as gear, plastic-fiber bags, sheeting, strapping, cloth, burlap bags, plastic 6-pack yokes. steel cable, aluminum beach lounge chairs, and polypropylene rope are also impli- cated,274.5h.65

15.5 FISHING A N D INCIDENTAL CAPTURE

In a comprehensive review of sources of mortality in sea turtles conducted by the National Academy of Science, incidental capture in shrimp trawls was said to account for more deaths than all other sources of human activities combined.27 Before the implementation of protective measures, direct mortality of an estimated 5.000 to 50.000 loggerheads and 500 to 5.000 Kemp's ridleys was believed to occur yearly

in U.S. waters ax a result of drowning in shrimp trawls." Sen tunics have also been killed when incidentally captured in purse seine, gill nets, and various types of untended fishing gear. Lobster and crab pots and hook and line fishing also cauw entanglement, mutilation, and debilitation. The mortalities associated with thew fishing categories are estimated to be about 10% of that attributed to shrimp trawling?'

Because sea turtles are exceptional breath-hold divers, there was initial skepti- cism about the estimated numbers of turtles caught and killed by inadvertent capture in trawls. This was shortly cast aside by a series of field and laboratory studies examining the impacts of enforced submergence. A study examining the relationship of tow time and sea turtle mortality showed that mortality was strongly dependent on trawling duration, with the proportion of dead or comatose sea turtles rising fmm 0% for the first 50 min of capture to 70% after 90 min capture." Loggerhead tunics captured in shrimp trawls with tow times of less than 30 min showed severe acidosis, and acid-base recovery times took as much as 20 hJ4 In laboratory and field studies, forcibly submerged loggerhead, green, and Kemp's ridley sea turtles suffered nub- stantial acidosis within 30 min, and also required many hours to restore a c i d - b ~ balance.".17 The physiological disruptions associated with enforced submergence (see Chapter 10) would be sufficient to cause a comatose state leading eventually to d e a ~ h . ~ ~ S e a turtles forcibly submerged in any type of restrictive fishing gear would eventually suffer fatal consequences from prolonged anoxia and/or seawater infll- tration of the lung.

15.5.1 SHRIMP TRAWLING AND TURTLE EXCLUDER DEVICES

In 1978. the U.S. National Marine Fisheries Service and Sea Grant Program under- took development of trawl modifications (turtle excluder device, or TED) that would allow captured sea turtles to escape the trawl through an escape hatch (Figures 15.3 and 15.4). By 1987. regulations required seasonal TED use in offshore shrimp trawlers from North Carolina to Texas, although these were not finalized and fully enforced until September 1989. Following years of unsuccessful voluntary compli- ance programs, legislation was passed in 1994 requiring year-round use of certified TEDs by U.S. shrimpers from North Carolina to Texas. The use of TEDs in South Carolina waters is believed to have reduced annual loggerhead strandings by 44%.79 Repeated capture by trawlers in intensely fished areas may cause some sea turtle mortality (despite the use of TEDs) in cases where sea turtles are unable to com- pensate for repeated metabolic stress.

Because of the high product value, shrimping intensity is high in coastal region! ~or ldwide .~ ' Given the highly migratoq nature of sea turtles, protective measures on the part of one country would shortly be undone by unrestricted fishing practices of adjacent countries. In order to conserve the sea turtles, mitigation of incidental catch must be addressed by all shrimp-fishing nations. In 1993. Mexico rquired that offshore trawlers use TEDs in Atlantic and Caribbean fishing zones. The concent and application of the TED has expanded, and these devices are now known "bycatch excluder devices" in recognition of their value in reducing undesired bycatch of finfish by as much as 50 to 70%?"The U.S. National Marine Fishenel

St':i turtles are :ilso viilncr;ihlc to c;1;>tiIre in ptbl;i~ic lor~ylinc. p;iirctl tr:1\1,1, ml ,vill m't Iislirriw. ;I soIirce of iric~rC:isini: t.oriL'cbrn fur holh fistierifs ni;in:iTrs ;ind [hr

industry. lnciclenl;il sc:i lnrllc hike en swordtisli ;ind tiin;i tishiny yr~)innIs 11;itl hren

If we are to protect sea turtles from further population decline we clearly need to encourage the development of fishing techniques that minimize or eliminate incidental take. This task is difficult to achieve until we understand the nature of sea turtle migration and foraging routes, particularly in offshore areas where migm- tion routes are poorly known. Incidental take records and anecdotal observations from the fisheries document a notable abundance of sea turtles on shelf break (200- m depth contour) or at edges of oceanic gyre systems such as the Gulf Stream western boundary and Gulf of Mexico Loop Current.33-34-57-ffl'88-89 New technologies such as satellite tracking, remote sensing of the environment, and other techniques may help quantify the types and degrees of interaction of sea turtles with human activities on the high seas. Observer programs and better recordkeeping by fishermen may also help quantify the impacts of fishing and offer solutions for mitigation efforts.

The worldwide decline of nearly all sea turtle populations can be attributed in part to the direct take of turtles and their eggs by commercial and subsistence sea turtle fisheries. Particularly in developing countries, the need for protein and income generated by sea turtles and their by-products greatly exceeds any desire for their preservation. Although all sea turtle life stages have been exploited, perhaps with the exception of hatchlings, breeding adults and their eggs have been most vulnerable. Nesting females and the eggs they leave buried in the sand have provided easy access to an otherwise difficult to reach resource. Mating areas and nearshore feeding grounds, particularly reefs frequented by hawksbills, also provide relatively easy access to large numbers of sea turtles.

In many cultures, sea turtle eggs are eaten not only for nutrition, but also because of purported aphrodisiac qualities. Green turtles are sought after primarily for their meat and cartilage (calipee). as well as their shells and bodies, which are sometimes stuffed and sold as curios for the tourist trade. Even bones are used to make houseware items, decorative artwork, ornaments, jewelry, and fertilizer.wy1 Pacific ridley skin is used to fashion boots, shoes, handbags, and other accessories, and oil rendered from the carcass is used for everything from skin lotion additives to boat caulking agents. Hawksbills are highly desired for their beautiful shells, which are polished and hung on the wall as a decorative ornament. or the scutes from their shells ("bekko") used to craft jewelry, combs, and eyeglasses.

Since prohibited by the Endangered Species Act of 1973. commercial sea turtle harvests no longer exist within continental U.S. waters, and were recently banned in Mexico.92 Sea turtle fisheries, nonetheless, continue elsewhere. Since the mid- 1970% the primary importers of sea turtle shell and skin have been Japan, Hong Kong, China, Singapore, Taiwan, and some European c o u n t r i e ~ . ~ ~ ' , ~ ~ The major exporters have been Panama. Honduras. Jamaica, Haiti. Cuba, Cayman Islands, Maldives, Fiji, Solomon Islands, Indonesia. Philippines, Thailand, Kenya, and Tan- ~ a n i a . ~ ~ ~ ' - ~ ~ These countries generally harvest only turtles from their beaches and territorial waters, and in many instances feel their activities are justified because they exploit their own resources. But in reality, sea turtles are highly migratory

species that, on a geouruphic scale, are a regional resource to he ni11naged and shared among many countries.

Commercial exploitation has resulted in overharvesting and in declines or local extinctions of the populations harvested. Unfortunately, the effects of a commercial harvest are not immediately apparent and may give the false impression that continued exploitation will not be detrimental to the population being harvested. This is best illustrated by the Pacific sea turtle fishery in Mexico which harvested hundreds of thousands of olive ridleys annually over several decades. This lead to the demise of at least three local nesting populations and a precipitous decline of the species in the eastern Pacific Ocean.",*

Legal and illegal subsistence sea turtle hunts and egg harvests occur worldwide, but in contrast to commercial sea turtle fisheries, they supply local markets or tribe^, and in some instances the international tourist trade.9' The level of subsistence take and the corresponding threat to a purlicular population is difficult to determine because the number of sea turtles and eggs taken generally is not documented or reported. In some regions subsistence hunts are controlled by annual quotas and appear to pose little threat to the resource." In other areas where quotas are nonex- istent, indigenous peoples have long ago exceeded the sustainable level of take and have extirpated sea turtle populations.

15.5 CONCLUSIONS

There is ample evidence that human activity is seriously eroding once abundant sek turtle populations. Much of the impact is unintentional, a consequence of the increased exploitation of marine and coastal waters - the more intense fishing effoIl results in an increase in the incidental catch of sea turtles and a higher risk of entanglement in discarded gear. Debris and pollution in coastal areas take their toll year after year. The inexorable spread of beach development eats away at natural sea turtle nesting habitats and deters nesting females. Even well-intentioned eco- tourism programs, which seek to educate visitors to turtle nesting beaches and offer alternative employment for subsistence turtle hunters, have the potential for harm. Poorly regulated foot traffic, noise, and lights create disturbances that may deter nesting females and threaten hatchlings. There are also deliberate threats to sea h d e survival, a consequence of both local economic pressures and international c o m e r - cia1 interests which drive continued (even if illegal) fishing for juveniles and adults and a massive taking of eggs.

In order to be biologically effective, conservation programs must be firmly based on knowledge of how and to what extent humans are jeopardizing turtle survival. In order to be accepted both politically and practically, conservation programs must also recognize the economic forces behind the disturbing influences. These will be different in different countries and even in different regions, so that implementable solutions are/will be complex. Nevertheless, action is urgently need to halt the decline and turn the situation around. Otherwise, the extinction of local populations and even some species is inevitable.

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Documents

Human Sea Turtle Survival · or taken by predat~rs.""~ Loggerhead hatchlings can escape from a 3-cm-deep footprint, but are unable to escape a tire rut of similar depth. Hatchlings