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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
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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
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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
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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
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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
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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.
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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.
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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,
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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
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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
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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
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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
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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
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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
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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.
Representative terms from entire chapter:
sea turtle
