The Leatherback Sea Turtle

 

 

The leatherback sea turtle is the largest of all the sea
turtles. It is also unique among sea turtles, because
instead of a bony carapace, it has leather-like outer
skin in which is embedded a mosaic of small bones. The
leatherback nests regularly in small numbers on the east
coast of Florida. The nesting and hatching season extends
from mid-February through mid-November. Sea turtles, in
general, are susceptible to human changes to the marine
environment, as well as to their nesting beaches. This
account provides an overview of the biology of the
leatherback sea turtle throughout its range. The discussion
of environmental threats and management activities,
however, pertains only to Florida and the U.S. Caribbean.
Serious threats to the leatherback turtle on its nesting
beaches include: artificial lighting, beach nourishment,
increased human presence, and exotic beach and dune
vegetation.
This account is from the 1992 Recovery Plan for
Leatherback Turtles in the U.S. Caribbean, Atlantic, and
Gulf of Mexico (NMFS and FWS 1992). Updated
information is included only for South Florida.
Description
The leatherback sea turtle is the largest of the sea turtles and
is so distinctive that it is placed in a separate family,
Dermochelyidae. The leatherback sea turtle possesses a
skeletal morphology unique among turtles (Rhodin et al.
1981) and recent karyological studies with this species
(Medrano et al. 1987) support classifications which segregate
extant sea turtle species into two distinct families (Gaffney
1975, 1984, Bickham and Carr 1983). All other extant sea
turtles are in the family Cheloniidae.
The carapace of the leatherback sea turtle is also different
from that of other sea turtles. Other sea turtles have bony
plates covered with horny scutes on the carapace, while the
slightly flexible carapace of the leatherback is distinguished
by a rubber-like texture. The carapace of the leatherback is
Leatherback Sea Turtle
Dermochelys coriacea
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Federal Status: Endangered (June 2, 1970)
Critical Habitat: Designated (September 1978
and March 1979): Sandy Point,
St. Croix, U.S.Virgin Islands, and
surrounding waters.
Florida Status: Endangered
Figure 1. Florida nesting distribution of the
leatherback sea turtle.
Recovery Plan Status: Contribution (May 1999)
Geographic Coverage: South Florida
about 4 cm thick and is made primarily of tough, oil-saturated connective tissue
raised into seven prominent longitudinal ridges and tapered to a blunt point
posteriorly. A nearly continuous layer of small dermal bones lies just below the
leathery outer skin of the carapace. No sharp angle is formed between the carapace
and the plastron, resulting in a barrel-shaped appearance. The front flippers are
proportionally longer than in other sea turtles and may span 270 cm in an adult.
The leatherback’s mean curved carapace length for adult females nesting in the
U.S. Caribbean is 155 cm (range 137 to 176). On Sandy Point NWR, weights of
262 kg to 506 kg have been recorded (Eckert and Eckert 1985, Basford et al. 1986,
Brandner et al. 1987). Adults and near adults captured in Virginia waters have
ranged from 137 to 183 cm curved carapace length (NMFS and FWS 1992). Size
and weight relationships calculated from adult females in St. Croix suggest the
Virginia leatherbacks range in weight from 204 to 696 kg. The largest leatherback
on record (a male stranded on the coast of Wales in 1988) weighed 916 kg
(Morgan 1989).
Leatherback hatchlings are dorsally mostly black and covered with tiny
polygonal or bead-like scales; the flippers are margined in white and rows of white
scales appear as stripes along the length of the back. In the U.S. Virgin Islands
hatchlings average 61.3 mm in straightline carapace length and 45.8 g in weight
(Eckert et al. 1984). Both front and rear flippers lack claws. In the adult the
epidermis is black (with varying degrees of pale spotting) and scaleless. This
scaleless condition is unique among sea turtles. The undersurface is mottled,
pinkish-white and black, the proportion of light to dark pigment being highly
variable. In both adults and hatchlings, the upper jaw bears two tooth-like
projections, each flanked by deep cusps, at the premaxillary-maxillary sutures
(Pritchard 1971).
The crawl of the nesting leatherback is very deep and broad, with symmetrical
diagonal marks left by the front flippers usually with a deep incised median
groove formed by dragging of the relatively long tail (Pritchard et al. 1983).
The internal anatomy and physiology of the leatherback is also distinctive.
The core body temperature, at least for adults in cold water, has been shown to be
several degrees C above the ambient temperature (Frair et al. 1972). This may be
due to several features, including the thermal inertia of a large body mass, an
insulating layer of subepidermal fat, countercurrent heat exchangers in the
flippers, potentially heat-generating brown adipose tissue, and a relatively low
freezing point for lipids (Mrosovsky and Pritchard 1971, Friar et al. 1972, Greer
et al. 1973, Neill and Stevens 1974, Goff and Stenson 1988, Davenport et al.
1990, Paladino et al. 1990). The skeleton of the leatherback remains extensively
cartilaginous, even in adult animals, and the species is unique among turtles in
showing an extensive cartilage canal vascular system in the epiphyseal regions
(Rhodin et al. 1981).
Taxonomy
The generic name Dermochelys was introduced by Blainville (1816). The
binomial refers to the distinctive leathery, scaleless skin of the adult turtle. The
specific name coriacea was first used by Vandelli (1761) and adopted by Linneaus
(1766) (see Rhodin and Smith 1982). Refer to Pritchard and Trebbau (1984) for a
more detailed discussion of taxonomy and synonymy.
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Distribution
The wide-ranging leatherback sea turtle nests on shores of the Atlantic, Pacific
and Indian Oceans. Non-breeding animals have been recorded as far north as
the British Isles and the maritime Provinces of Canada and as far south as
Argentina and the Cape of Good Hope (Pritchard 1992).
Efforts to determine the distribution and numbers of leatherback sea turtles
in the marine environment have met with varying degrees of success. A 1987
aerial survey of shallow Gulf of Mexico waters (Perdido Bay, Alabama to Cape
San Blas, Florida) described leatherbacks as “uncommon” in all study areas
(though relatively more common in autumn than in spring), the highest density
being 0.027 leatherbacks/100 km2 offshore Louisiana in October (Lohoefener
et al. 1988). Earlier surveys (April 1982 to February 1983) in the Atlantic
revealed leatherbacks in the study area (Key West, Florida to Cape Hatteras,
North Carolina, out to the western boundary of the Gulf Stream) year-round,
but no density estimates were given (Thompson 1984). Thompson (1984)
reported a significant negative correlation between leatherbacks and water
temperature in the spring, fall and winter, suggesting that the species is not
dependent upon warm temperatures and is likely to be associated with cooler,
perhaps more productive waters. The same study reported that leatherbacks
appeared to prefer water about 20°C (± 5°) and were rarely sighted in the Gulf
Stream sampling areas. Summarizing incidental catch and interview data (1897
to 1980), as well as at-sea observations recorded during shore to Gulf Stream
summer transects, Lee and Palmer (1981) also concluded that (at least off
North Carolina) leatherbacks were rarely seen in the Gulf Stream and were
most often seen in waters < 915 m in depth.
A survey conducted during March 1982 to August 1984, but restricted to
the Cape Canaveral area, reported that 94.5 percent of all leatherback sightings
(n=128 total) occurred east of the 20 m isobath, and 90.6 percent occurred
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
Juvenile leatherback sea turtle.
Original photograph courtesy
of U.S. Fish and Wildlife Service.
during the summer (Schroeder and Thompson 1987). In contrast, New England
Aquarium surveys of Florida and Georgia (1984 to 1988) reported few
leatherbacks prior to 1988, but in mid-February of that year 168 leatherbacks
were sighted along the northeast coast of Florida, with peak densities reported
along 80 km of coastline between Daytona Beach and Cape Canaveral
(Knowlton and Weigle 1989). The impetus for this sudden winter abundance in
Florida nearshore waters is unknown; by the following survey (16 March) the
animals had disappeared (Knowlton and Weigle 1989). The extent to which
distribution and abundance are defined by transient phenomena is presently
unclear.
A 1979 aerial survey of the mid- and north-Atlantic areas of the U.S. Outer
Continental Shelf (shoreline to the surface projection of the 2,000 m isobath)
between Cape Hatteras, North Carolina and Cape Sable, Nova Scotia, showed
leatherbacks to be present April to November throughout the study area (but
most likely to be observed from the Gulf of Maine south to Long Island); peak
estimates of relative abundances during the summer were in the hundreds
(Shoop et al. 1981). The same study concluded that leatherbacks were
observed more frequently in colder waters at higher latitudes during the
summer than were other sea turtle species.
Nesting grounds for the leatherback are distributed circumglobally (ca.
40°N to 35°S; Sternberg 1981), with the Pacific coast of Mexico supporting the
world’s largest known concentration of nesting turtles. Pritchard (1982)
estimates that 115,000 adult female leatherbacks remain worldwide and that
some 50 percent of them may nest in western Mexico. The largest nesting
colony in the wider Caribbean region is found at Ya:lima:po-Les Hattes, French
Guiana, where the total number of adult females is estimated to be 14,700 to
15,300 (Fretey and Girondot 1989). Lower density Caribbean nesting is also
reported from Surinam (Pritchard 1973, Schulz 1975), Guyana (Pritchard
1988a,b), Colombia and Venezuela (Pritchard and Trebbau 1984), Panama
(Meylan et al. 1985, Garcia 1987), and Costa Rica (e.g., Carr and Ogren 1959,
Hirth and Ogren 1987).
On the islands of the eastern Caribbean, Bacon (1970) estimated that 150
to 200 leatherbacks nested annually in Trinidad, primarily at Matura and Paria
bays. Shortly thereafter, Bacon and Maliphant (1971) indicated that perhaps
200 to 250 leatherbacks nested annually in Trinidad; recent population
estimates are not available. Nesting north of Trinidad in the Lesser and Greater
Antilles is predictable, but occurs nowhere in large numbers (Caldwell and
Rathjen 1969, Carr et al. 1982, Meylan 1983). The largest sub-regional nesting
colony is in the Dominican Republic, where an estimated 300 leatherbacks nest
annually (Ross and Ottenwalder 1983). The U.S. Caribbean supports relatively
minor nesting colonies (probably 150-200 adult females per annum, combined)
but represents the most significant nesting activity within the U.S.
Leatherback nesting in the U.S. Caribbean is reported from the Virgin
Islands (St. Croix, St. Thomas, St. John) and Puerto Rico, including Islas
Culebra, Vieques, and Mona. The total number of nests deposited annually on
Sandy Point NWR has ranged from 82 (1986) to 355 (1994) (Eckert and Eckert
1985, Basford et al. 1986, 1988, McDonald et al. 1991, 1992, 1993, 1994). On
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
Isla Culebra, the colony is smaller (88 to 271 nests per year 1984 to 1995,
Tallevast et al. 1990, FWS unpublished reports). Playas Resaca and Brava
receive 91 to 100 percent of all leatherback nesting on Culebra (Tucker 1988).
Throughout the southeastern U.S. the geography of beach coverage is more
or less complete, but the timing is often inadequate to gain a complete picture
of leatherback nesting. Beach patrols generally commence in May and are
designed to maximize observations of leatherback sea turtle nests. However,
leatherbacks have been known to start nesting as early as late February or
March, thus, current data may slightly underestimate the actual nesting activity.
Leatherback nests reported from Florida and Georgia are probably deposited
by 10 to 25 females annually. Leatherback turtles have been known to nest in
Georgia and South Carolina, but only on rare occasions. Hildebrand (1963)
was informed by a resident of Padre Island, Texas that a few nesting
individuals had been seen on the island in the 1930s, but none in recent years.
Leatherback nesting in Florida was once considered extremely rare (Carr
1952, Caldwell et al. 1956, Allen and Neill 1957). However, the leatherback is
now known to nest regularly in small numbers on Florida’s east coast (Meylan
et al. 1995). Leatherback nesting has also been reported on the west coast of
Florida on St. Vincent NWR (LeBuff 1990), St. Joseph Peninsula State Park
and St. George Island (S. MacPherson, FWS, personal communication 1997).
In South Florida, leatherbacks have been observed on nesting beaches in Indian
River, St. Lucie, Martin, Palm Beach, Broward and Miami-Dade counties on
the east coast (Figure 1).
Virtually nothing is known of the pelagic distribution of hatchling or
juvenile leatherback turtles. The paths taken by hatchlings leaving their natal
beaches are uncharted. Discussions of the “lost year” (the early pelagic stage
of sea turtle development) which include tabulated summaries of neonate and
juvenile sea turtles associated with Sargassum weed or taken from pelagic
habitats (e.g., Carr 1987) have not mentioned sightings of young Dermochelys.
Our knowledge of juvenile distribution rests on a handful of chance
observations, and includes sightings in waters within (Caldwell 1959, Johnson
1989) and outside (e.g., Brongersma 1970, Hughes 1974, Pritchard 1977,
Horrocks 1987) the U.S.
Strandings
Leatherbacks stranding on U.S. shores are generally of adult or near adult size,
demonstrating the importance of pelagic habitat under U.S. jurisdiction to
turtles breeding in tropical and subtropical latitudes. Direct evidence of this is
available from Caribbean and South American tagged turtles stranding on U.S.
shores. Nesters tagged in French Guiana subsequently stranded in Georgia
(NMFS and FWS 1992), as well as in New York (NMFS and FWS 1992), New
Jersey, South Carolina, and Texas (Pritchard 1976). Nesters tagged in Trinidad
and St. Croix subsequently stranded in New York (Lambie 1983) and New
Jersey (Boulon et al. 1988), respectively. Conversely, an individual tagged in
Virginia waters in 1985 was killed a year later in Cuba (Barnard et al. 1989).
Additional evidence of the importance of U.S. coastal waters for leatherbacks
is provided by the Sea Turtle Stranding and Salvage Network. During the
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
period 1980 to 1991, 816 leatherback strandings were recorded along the
continental U.S. coastline. During this same period, 161 leatherbacks were
recovered dead along Florida’s coast. Curved carapace lengths for the Florida
strandings ranged from 110 to 195 cm. Eighty-four percent of all leatherback
strandings in Florida occurred between January to April and October to
December. Strandings were lowest (16 percent) during summer months, May
to September.
Habitat
Adult leatherback sea turtles are highly migratory and believed to be the most
pelagic of all sea turtles. Habitat requirements for juvenile and post-hatchling
leatherbacks, however, are virtually unknown. Nesting females prefer highenergy
beaches with deep, unobstructed access (Hirth 1980, Mrosovsky 1983),
which occur most frequently along continental shorelines (Hendrickson 1980).
Critical Habitat
Critical habitat was designated for the leatherback sea turtle in September
1978 and March 1979. Although the designation did not include Florida, is
does include nesting beach on Sandy Point, St. Croix and the surrounding
waters. Critical habitat for leatherback sea turtles identify specific areas which
have those physical or biological features essential to the conservation of the
leatherback sea turtle and/or may require special management considerations.
Behavior
Reproduction and Demography
Mating behavior of the leatherback is described by Carr and Carr (1986) in
waters off Puerto Rico, though there is some indirect evidence that mating
typically occurs prior to (or during) migration to the nesting ground (Eckert
and Eckert 1988). Nesting behavior (i.e., the basic sequence entailing
beaching, ascent, selection of a suitable site, “body pitting”, egg chamber
excavation, oviposition, nest filling and camouflage, departure) is similar to
that of other marine turtle species (detailed descriptions in Deraniyagala 1936,
Carr and Ogren 1959). Gravid females emerge from the sea nocturnally;
diurnal nesting occurs only occasionally. Because of a proclivity for nesting in
high-energy and thus frequently unpredictable environments, it is not
uncommon that large numbers of eggs are lost to erosion (Bacon 1970,
Pritchard 1971, Hughes 1974, Mrosovsky 1983, Eckert 1987), though this is
not always the case (Tucker 1989). While the majority of females return to the
same nesting beach repeatedly throughout the nesting season, some females are
known to nest on separate beaches > 100 km apart within a season.
In the U.S. Caribbean, nesting commences in March (a very few nests are
laid in February) and continues into July. The most systematic data available on
reproductive output has been gathered at Sandy Point NWR and Isla Culebra.
Data from these projects reveal that females arrive at the nesting beach
asynchronously, renest an average of every 9 to 10 days, deposit 5 to 7 nests per
annum (observed maximum = 11), and remigrate predominantly at 2 to 3 year
intervals. The annual nest : false crawl ratio on Culebra (all beaches) is 4:1 to
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
6.2:1 (1984 to 1987; Tucker 1988); 1.2:1 to 3:1 on Sandy Point (1982-1988;
NMFS and FWS 1992). Clutch size averages 116 eggs, including 80 yolked eggs,
on Sandy Point NWR, 103 eggs, including 70 yolked eggs, on Culebra. Clutch
size averages 101 eggs, including 76 yolked, on Hutchinson Island, Florida
(NMFS and FWS 1992). Similar clutch sizes are reported elsewhere on St. Croix
(Adams 1988) and Puerto Rico (Matos 1986, 1987), as well as in Georgia
(Ruckdeschel et al. 1982) and Florida (Carr 1952, Caldwell 1959, Broward
County Erosion Prevention District/Environmental Quality Control Board--now
Department of Natural Resource Protection--1987). Eggs incubate for 55 to 75
days, consistently averaging 63 days on both Sandy Point and Culebra and 64
days on Hutchinson Island, Florida. In situ hatch success for nests surviving to
term is about 55 percent on Manchenil Bay, St. Croix (Adams 1988), about 65
percent on Sandy Point NWR (Eckert and Eckert 1985, Brandner et al. 1987,
1990), and about 66 percent on Hutchison Island, Florida (NMFS and FWS
1992). Higher success (about 75 percent) is reported on Culebra (Tucker 1988,
1989).
No data on the growth rate of juvenile leatherback turtles in the wild are
available. This situation arises from the unfortunate fact that the distribution of
juvenile leatherback turtles is unknown, and thus specimens are unavailable for
capture-recapture methodologies designed to measure growth. The problem is
exacerbated by poor survivability in captivity, which further limits
opportunities for study. Nonetheless, some investigators have been successful
in raising leatherbacks and publishing data on captive growth rates
(Deraniyagala 1936, Glusing 1967, Frair 1970, Spoczynska 1970, Phillips
1977, Witham 1977, Bels et al. 1988). With the exception of Bels et al. (1988),
turtles did not survive beyond 2 years.
Captive growth data are widely disparate, but the very rapid growth
reported by some investigators (coupled with evidence of chondro-osseous
development conducive to rapid growth) has led to speculations that
leatherbacks may reach sexual maturity in 2 to 3 years (Rhodin 1985). Bels et
al. (1988) challenge this hypothesis in their report of a healthy captive
leatherback 1,200 days of age weighing 28.5 kg, with a carapace 82 cm in
length. While leatherbacks may grow to sexual maturity at an earlier age than
other sea turtles, it is clear that more data are needed before growth rates can
be accurately calculated.
Migration
The leatherback migrates farther (Pritchard 1976) and ventures into colder
water than does any other marine reptile (e.g., Threlfall 1978, Goff and Lien
1988). The evidence currently available from tag returns and strandings in the
western Atlantic suggests that adults engage in routine migrations between
boreal, temperate and tropical waters, presumably to optimize both foraging
and nesting opportunities (Bleakney 1965, Pritchard 1976, Lazell 1980,
Rhodin and Schoelkopf 1982, Boulon et al. 1988). The composition of
epibiotic barnacle communities on Caribbean-nesting leatherbacks provides
indirect evidence that gravid females embark from and subsequently return to
temperate latitudes (Eckert and Eckert 1988).
Direct evidence of long-distance movement is scarce, but is available from
leatherbacks tagged while nesting in the Caribbean and subsequently stranding
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
in northern latitudes (Pritchard 1973, 1976, Lambie 1983, Boulon et al. 1988);
and also from a turtle tagged in Chesapeake Bay in 1985 and killed in Cuba in
1986 (Barnard et al. 1989). In addition, a nester tagged at Jupiter Beach,
Florida, was recaptured near Cayo Arcas, Gulf of Campeche (Hildebrand
1987), and a nester tagged at Sandy Point NWR, St. Croix, was recaptured near
Cayos Triangulos, also in the Gulf of Campeche, 2 years later and some 3,000
km from the tagging site (Boulon 1989). The longest known movement is that
of an adult female who traveled 5,900 km to Ghana, West Africa, after nesting
in Surinam (Pritchard 1973). An adult female tagged with a satellite transmitter
while nesting in French Guiana in 1986 traveled 820 km in three weeks (an
average speed of 40 km/day, Duron-DuFrenne 1987). A nester tagged with a
satellite transmitter on Sandy Point NWR, St. Croix in 1989 travelled 515 km
(and ventured some 200 km south of St. Croix) before the transmitter was
removed 18 days later when the turtle emerged to nest on Isla Culebra (NMFS
and FWS 1992).
Foraging
Food habits are known primarily from the stomach samples of slaughtered
animals (Brongersma 1969, Hartog 1980, Hartog and Van Nierop 1984).
Leatherbacks feed on pelagic medusae (jellyfish), siphonophores, and salpae in
temperate and boreal latitudes (e.g., Bleakney 1965, Brongersma 1969, Duron
1978, Eisenberg and Frazier 1983, Musick 1988). Aerial surveys document
leatherbacks in Virginia waters, especially May to July during peak jellyfish
(Chrysaora spp., Aurelia spp.) abundance (Musick 1988, NMFS and FWS
1992). Further south, foraging on the cabbage head jellyfish (Stomolophus
meleagris) has been observed in waters off North Carolina (NMFS and FWS
1992). In February 1989, an adult female leatherback (originally tagged in
French Guiana) stranded on the Georgia coast and stomach contents revealed
unidentified medusae and Libinia sp., a small crab commensal on Stomolophus
(NMFS and FWS 1992). Captain Joe Webster has observed leatherbacks feeding
on “jellyballs” (Stomolophus) in Georgia waters and notes that the turtles are seen
in water as shallow as 5.6 m where jellyballs are abundant (NMFS and FWS
1992). In the Gulf of Mexico, aerial survey data often show leatherbacks
associated with Stomolophus (Leary 1957, Lohoefener et al. 1988). Other
observers have also reported a “co-incidence” of leatherbacks and maximum
jellyfish abundance, especially Aurelia, in the Gulf (NMFS and FWS 1992).
Foraging has most often been observed at the surface, but Hartog (1980)
after finding nematocysts from deep water siphonophores in leatherback stomach
samples, speculated that foraging may occur at depth. Limpus (1984) reported a
leatherback feeding on octopus bait on a handline at 50 m depth off western
Australia. Based on offshore studies of diving by adult females nesting on St.
Croix, Eckert et al. (1989) proposed that the observed internesting dive behavior
reflected nocturnal feeding within the deep scattering layer (strata comprised
primarily of vertically migrating zooplankters, chiefly siphonophore and salp
colonies in the Caribbean, (Michel and Foyo 1976). Eckert et al. (1989) calculate
a maximum dive depth of 1,300 m, but report that 95 percent of all dives are <
20 minutes in length and < 200 m in depth.
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Relationship to Other Species
In South Florida, the leatherback sea turtle shares nesting beaches with the
threatened loggerhead turtle (Caretta caretta) and the endangered green sea turtle
(Chelonia mydas) in several counties where it nests, most commonly in Martin
and Palm Beach counties. Other federally listed species that occur in coastal dune
and coastal strand habitat, and that need to be considered when managing nesting
beaches, are the southeastern beach mouse (Peromyscus polionotus niveiventris)
and the beach jacquemontia (Jacquemontia reclinata). Beach nourishment
projects, in particular, could affect these species as well as the turtles. The range
of the beach mouse in South Florida is estimated to include Indian River County
south to Broward County. The beach jacquemontia is found in Palm Beach
County south to Miami, Miami-Dade County.
A variety of natural and introduced predators such as raccoons (Procyon
lotor), feral hogs, opossums (Didelphis virginiana), ghost crabs (Ocypode
quadratus), and ants prey on incubating eggs and hatchlings. The principal
predator of leatherback sea turtle eggs is the raccoon. Raccoons are particularly
destructive and may take up to 96 percent of all nests deposited on a beach (Davis
and Whiting 1977, Hopkins and Murphy 1980, Stancyk et al. 1980, Talbert et al.
1980, Schroeder 1981, Labisky et al. 1986). In 1996, Hobe Sound NWR
experienced depredation in 23 percent of the nests enumerated. In addition to the
destruction of eggs, certain predators may take considerable numbers of
hatchlings just prior to or upon emergence from the sand.
Status and Trends
The leatherback sea turtle was listed as endangered under the Endangered
Species Act on June 2, 1970 (35 FR 8495). Internationally, it is considered
“endangered” by the International Union for Conservation of Nature and
Natural Resources (IUCN). It is also included on Appendix I of the Convention
on International Trade in Endangered Species of Wild Fauna and Flora
(CITES), which the U.S. ratified in 1974. The nesting beach at Sandy Point
NWR, St. Croix, became the first nesting beach of any marine turtle to be
proposed as critical habitat (Federal Register, 23 March 1978; 43 FR 12050-
12051) (Dodd 1978). In September 1978, the FWS designated the nesting
beach on Sandy Point, St. Croix, as critical habitat; in March 1979, the NMFS
determined the surrounding waters as critical habitat.
Declines in the number of nesting females have been documented in
Malaysia (Brahim et al. 1987), India (Cameron 1923, Kar and Bhaskar 1982),
Thailand (Polunin 1977), and the West Indies (Bacon 1970, Eckert and
Lettsome 1988, Eckert 1989). It is not known whether leatherback populations
within the U.S. are stable, increasing or declining, but there is no question that
some nesting populations (e.g., St. John, St. Thomas) have been virtually
exterminated. The number of leatherbacks nesting in the past at what is now
Sandy Point NWR is unknown, but studies of the population since 1981 show
annual fluctuations which do not project a long-term decline.
Today, most beaches in Florida are monitored for sea turtle nesting. Here,
leatherback nesting has fluctuated widely during the survey period between
1979 and 1994 (Meylan et al. 1995, DEP 1996). Between 1988 and 1992,
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County Average
Indian River* 3.3
St. Lucie 14
Martin 43
Palm Beach 66
Broward 10
Dade 3.2
Monroe** -
Collier** -
Lee** -
Charlotte** -
Sarasota** -
Table 1. Average number
of leatherback nests by
*Nesting activity reported
from 1993-1995 only
**Nesting activity not
reported
annual reported leatherback sea turtle nests varied between 98 and 188
statewide. The distribution of these nests differs from the loggerhead and green
sea turtle nests. Leatherback nests have a center of distribution at Palm Beach
County which supports half of the total nests reported throughout Florida.
Martin and St. Lucie county beaches have been the site of 27.7 percent and
13.2 percent of leatherback nests, respectively. South of Palm Beach County,
the number of leatherback nests declines more sharply. Broward County
supported 3.0 percent of leatherback nesting and Miami-Dade County
supported 1.6 percent.
The average number of nests annually for leatherback turtles within South
Florida is shown in Table 1. These data show that Palm Beach County is clearly
the most important nesting location within the region for the endangered
leatherback. Leatherback nests constitute 0.8 percent of the total in Palm Beach
County but only 0.4 and 0.5 percent in Broward and Miami-Dade Counties,
respectively. We chose to represent only the past 10 years of survey data in
Table 1, because there was less beach surveyed and the data were not complete
prior to 1985.
Environmental Threats
A number of threats exist to sea turtles in the marine environment, including: oil
and gas exploration, development, and transportation; pollution; trawl, purse
seine, hook and line, gill net, pound net, longline, and trap fisheries; underwater
explosions; dredging; offshore artificial lighting; power plant entrapment;
entanglement in debris; ingestion of marine debris; marina and dock development;
boat collisions; and poaching. These threats and protective measures are discussed
in detail in the Recovery Plan for Leatherback Turtles in the U.S. Caribbean,
Atlantic and Gulf of Mexico (NMFS and FWS 1992). In South Florida, and for
this Recovery Plan, we are focusing on the threats to nesting beaches, including:
beach erosion, armoring and nourishment; artificial lighting; beach cleaning;
increased human presence; recreational beach equipment; exotic dune and beach
vegetation; nest loss to abiotic factors; and poaching.
Beach Erosion: Erosion of nesting beaches can result in partial or total loss
of suitable nesting habitat. Erosion rates are influenced by dynamic coastal
processes, including sea level rise. Man’s interference with these natural
processes through coastal development and associated activities has resulted in
accelerated erosion rates and interruption of natural shoreline migration
(National Research Council 1990).
Beach Armoring: Where beachfront development occurs, the site is often
fortified to protect the property from erosion. Virtually all shoreline
engineering is carried out to save structures, not dry sandy beaches, and
ultimately results in environmental damage. One type of shoreline engineering,
collectively referred to as beach armoring, includes sea walls, rock revetments,
riprap, sandbag installations, groins and jetties. Beach armoring can result in
permanent loss of a dry nesting beach through accelerated erosion and
prevention of natural beach/dune accretion and can prevent or hamper nesting
females from accessing suitable nesting sites. Clutches deposited seaward of
these structures may be inundated at high tide or washed out entirely by
increased wave action near the base of these structures.
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
As these structures fail and break apart, they spread debris on the beach
trapping both adults and hatchlings, thus impeding access to suitable nesting
areas and causing higher incidences of false crawls (non-nesting emergences).
Sandbags are particularly susceptible to rapid failure and result in extensive
debris on nesting beaches. Rock revetments, riprap, and sandbags can cause
nesting turtles to abandon nesting attempts or to construct improperly sized and
shaped egg cavities when inadequate amounts of sand cover these structures.
Information obtained during preparation of the sea turtle recovery plans
indicated that approximately 21 percent (234 km) of Florida’s beaches were
armored at that time (NMFS and FWS 1992).
Groins and jetties are designed to trap sand during transport in longshore
currents or to keep sand from flowing into channels in the case of the latter.
These structures prevent normal sand transport and accrete beaches on one
side, of the structure while starving neighboring beaches on the other side
thereby resulting in severe beach erosion (Pilkey et al. 1984) and
corresponding degradation of suitable nesting habitat.
Drift fences, also commonly called sand fences, are erected to build and
stabilize dunes by trapping sand moving along the beach and preventing
excessive sand loss. Additionally, these fences can serve to protect dune
systems by deterring public access. Constructed of narrowly spaced wooden or
plastic slats or plastic fabric, drift fences when improperly placed can impede
nesting attempts and/or trap emergent hatchlings and nesting females.
Beach Nourishment: Beach nourishment consists of pumping, trucking, or
scraping sand onto the beach to rebuild what has been lost to erosion. Although
beach nourishment may increase the potential nesting area, significant adverse
effects to sea turtles may result if protective measures are not taken. Placement
of sand on an eroded section of beach or an existing beach in and of itself may
not provide suitable nesting habitat for sea turtles.
Beach nourishment can impact turtles through direct burial of nests and by
disturbance to nesting turtles if conducted during the nesting season. Beach
nourishment may result in changes in sand density (compaction), beach shear
resistance (hardness), beach moisture content, beach slope, sand color, sand
grain size, sand grain shape, and sand grain mineral content, if the placed sand
is dissimilar from the original beach sand (Nelson and Dickerson 1988a).
These changes can affect nest site selection, digging behavior, incubation
temperature (and hence sex ratios), gas exchange parameters within incubating
nests, hydric environment of the nest, hatching success and hatchling emerging
success (Mann 1977, Ackerman 1980, Mortimer 1982, Raymond 1984a).
Beach compaction and unnatural beach profiles that may result from beach
nourishment activities could adversely affect sea turtles regardless of the
timing of the projects. Very fine sand and/or the use of heavy machinery can
cause sand compaction on nourished beaches (Nelson and Dickerson 1988a).
Significant reductions in nesting success have been documented on severely
compacted nourished beaches (Raymond 1984a). Increased false crawls result
in increased physiological stress to nesting females. Sand compaction may
increase the length of time required for female sea turtles to excavate nests,
also causing increased physiological stress to the animals (Nelson and
Dickerson 1988c). Nelson and Dickerson (1988b) evaluated compaction levels
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
at 10 renourished east coast Florida beaches and concluded that 50 percent
were hard enough to inhibit nest digging, 30 percent were questionable as to
whether their hardness affected nest digging, and 20 percent were probably not
hard enough to affect nest digging. They further concluded that, in general,
beaches nourished from offshore borrow sites are harder than natural beaches,
and, while some may soften over time through erosion and accretion of sand,
others may remain hard for 10 years or more.
On nourished beaches, steep escarpments may develop along their water
line interface as they adjust from an unnatural construction profile to a more
natural beach profile (Coastal Engineering Research Center 1984, Nelson and
Dickerson 1987). These escarpments can hamper or prevent access to nesting
sites. Female turtles coming ashore to nest can be discouraged by the formation
of an escarpment, leading to situations where they choose marginal or
unsuitable nesting areas to deposit eggs (e.g., in front of the escarpments,
which often results in failure of nests due to repeated tidal inundation). This
effect can be minimized by leveling the beach prior to the nesting season.
A change in sediment color due to beach nourishment could change the
natural incubation temperatures of nests. This, in turn, could alter natural sex
ratios. To provide the most suitable sediment for nesting sea turtles, the color
of the nourished sediments must resemble the natural beach sand in the area.
Natural reworking of sediments and bleaching from exposure to the sun would
help to lighten dark nourishment sediments; however, the time frame for
sediment mixing and bleaching to occur could be critical to a successful sea
turtle nesting season.
Nourishment projects result in heavy machinery, pipelines, increased human
activity and artificial lighting on the project beach. These activities are normally
conducted on a 24-hour basis and can adversely affect nesting and hatching
activities. Pipelines and heavy machinery can create barriers to nesting females
emerging from the surf and crawling up the beach, causing a higher incidence of
false crawls (non-nesting emergences) and an unnecessary energy expenditure.
Increased human activity on the project beach at night may cause further
disturbance to nesting females. Artificial lights along the project beach and in the
nearshore area of the borrow site may deter nesting females and disorient or
misorient emergent hatchlings from adjacent non-project beaches.
Beach nourishment projects require continual maintenance (subsequent
nourishment) as beaches erode; therefore their negative impacts to turtles are
repeated on a regular basis. Nourishment of highly eroded beaches (especially
those with a complete absence of dry beach) can be beneficial to nesting turtles
if conducted properly. Careful consideration and advance planning and
coordination must be carried out to ensure timing, methodology, and sand
sources are compatible with nesting and hatching requirements.
Artificial Lighting: Extensive research has demonstrated that the principal
component of the sea finding behavior of emergent hatchlings is a visual
response to light (Daniel and Smith 1947, Hendrickson 1958, Carr and Ogren
1960, Ehrenfeld and Carr 1967, Dickerson and Nelson 1989, Witherington and
Bjorndal 1991). Artificial beachfront lighting from buildings, streetlights, dune
crossovers, vehicles and other types of beachfront lights have been
documented in the disorientation (loss of bearings) and misorientation
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
(incorrect orientation) of hatchling turtles (McFarlane 1963, Philibosian 1976,
Mann 1977, Ehrhart 1983).
The results of disorientation or misorientation are often fatal. Many
lighting ordinance requirements do not become effective until 11 p.m., whereas
over 30 percent of hatchling emergence occurs prior to this time (Witherington
et al. 1990). As hatchlings head toward lights or meander along the beach, their
exposure to predators and likelihood of desiccation is greatly increased.
Misoriented hatchlings can become entrapped in vegetation or debris, and
many hatchlings are found dead on nearby roadways and in parking lots after
being struck by vehicles. Hatchlings that successfully find the water may be
misoriented after entering the surf zone or while in nearshore waters. Intense
artificial lighting can even draw hatchlings back out of the surf (Daniel and
Smith 1947, Carr and Ogren 1960). During the period 1989 to 1990, a total of
37,159 misoriented hatchlings were reported to the Florida Department of
Natural Resources. Undoubtedly a large but unquantifiable number of
additional misorientation events occurred but were not documented due to
obliteration of observable sign, depredation, entrapment in thick vegetation,
loss in storm drains, or obliteration of carcasses by vehicle tires.
The problem of artificial beachfront lighting is not restricted to hatchlings.
Raymond (1984a) indicated that adult loggerhead emergence patterns were
correlated with variations in beachfront lighting in south Brevard County,
Florida, and that nesting females avoided areas where beachfront lights were
the most intense. Witherington (1986) noted that loggerheads aborted nesting
attempts at a greater frequency in lighted areas. Problem lights may not be
restricted to those placed directly on or in close proximity to nesting beaches.
The background glow associated with intensive inland lighting, such as that
emanating from nearby large metropolitan areas, may deter nesting females
and disorient or misorient hatchlings navigating the nearshore waters.
Cumulatively, along the heavily developed beaches of the southeastern U.S.,
the negative effects of artificial lights are profound.
Beach Cleaning: Beach cleaning refers to the removal of both abiotic and
biotic debris from developed beaches. There are several methods employed
including mechanical raking, hand raking, and picking up debris by hand.
Mechanical raking can result in heavy machinery repeatedly traversing nests
and potentially compacting sand above nests and also results in tire ruts along
the beach, which may hinder or trap emergent hatchlings. Mann (1977)
suggested that mortality within nests may increase when externally applied
pressure from beach cleaning machinery is exerted on soft beaches with large
grain sand. Mechanically pulled rakes and hand rakes can penetrate the surface
and disturb the sealed nest or may actually uncover pre-emergent hatchlings
near the surface of the nest. In some areas, collected debris is buried directly
on the beach, and this can lead to excavation and destruction of incubating egg
clutches. Disposal of debris near the dune line or on the high beach can cover
incubating egg clutches and subsequently hinder and entrap emergent
hatchlings and may alter natural nest temperatures.
Increased Human Presence: Residential and tourist use of developed (and
developing) nesting beaches can result in negative impacts to nesting turtles,
incubating egg clutches, and hatchlings. The most serious threat caused by
increased human presence on the beach is the disturbance to nesting females.
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
Nighttime human activity can cause nesting females to abort nesting attempts
at all stages of the behavioral process. Murphy (1985) reported that disturbance
can cause turtles to shift their nesting beaches, delay egg laying, and select
poor nesting sites. Heavy utilization of nesting beaches by humans (pedestrian
traffic) may result in lowered hatchling emerging success rates due to
compaction of sand above nests (Mann 1977), and pedestrian tracks can
interfere with the ability of hatchlings to reach the ocean (Hosier et al. 1981).
Campfires and the use of flashlights on nesting beaches misorient hatchlings
and can deter nesting females (Mortimer 1979).
Recreational Beach Equipment: The placement of physical obstacles (e.g.,
lounge chairs, cabanas, umbrellas, Hobie cats, canoes, small boats and beach
cycles) on nesting beaches can hamper or deter nesting attempts and interfere
with incubating egg clutches and the sea approach of hatchlings. The
documentation of false crawls at these obstacles is becoming increasingly
common as more recreational beach equipment is left in place nightly on
nesting beaches. Additionally, there are documented reports of nesting females
becoming entrapped under heavy wooden lounge chairs and cabanas on South
Florida nesting beaches (NMFS and FWS 1992). The placement of recreational
beach equipment directly above incubating egg clutches may hamper
hatchlings during emergence and can destroy eggs through direct invasion of
the nest (NMFS and FWS 1992).
Exotic Dune and Beach Vegetation: Non-native vegetation has invaded
many coastal areas and often outcompetes native species such as sea oats,
railroad vine, sea grape, dune panic grass and pennywort. The invasion of less
stabilizing vegetation can lead to increased erosion and degradation of suitable
nesting habitat. Exotic vegetation may also form impenetrable root mats which
can prevent proper nest cavity excavation, invade and desiccate eggs, or trap
hatchlings. The Australian pine (Casuarina equisetifolia) is particularly
detrimental. Dense stands of this species have taken over many coastal strand
areas throughout central and South Florida. Australian pines cause excessive
shading of the beach that would not otherwise occur. Studies in Florida suggest
that nests laid in shaded areas are subjected to lower incubation temperatures,
which may alter the natural hatchling sex ratio. Fallen Australian pines limit
access to suitable nest sites and can entrap nesting females. Davis and Whiting
(1977) reported that nesting activity declined in Everglades National Park
where dense stands of Australian pine took over native beach berm vegetation
on a remote nesting beach. Conversely, along highly developed beaches,
nesting may be concentrated in areas where dense stands of Australian pines
create a barrier to intense beachfront and beach vicinity lighting.
Nest Loss to Abiotic Factors: Erosion or inundation and accretion of sand
above incubating nests appear to be the principal abiotic factors that may
negatively affect incubating egg clutches. While these factors are often widely
perceived as contributing significantly to nest mortality or lowered hatching
success, few quantitative studies have been conducted. Studies on a relatively
undisturbed nesting beach by Witherington (1986) indicated that excepting a late
season severe storm event, erosion and inundation played a relatively minor role
in destruction of incubating nests. Inundation of nests and accretion of sand
above incubating nests as a result of the late season storm played a major role in
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
destroying nests from which hatchlings had not yet emerged. Severe storm events
(e.g., tropical storms and hurricanes) may result in significant nest loss, but these
events are typically aperiodic rather than annual occurrences. In the southeastern
U.S., severe storm events are generally experienced after the peak of the hatching
season and hence would not be expected to affect the majority of incubating
nests. Erosion and inundation of nests are exacerbated through coastal
development and shoreline engineering. These threats are discussed above under
beach armoring.
Predation: Predators, particularly exotics such as fire ants (Solenopsis
invicta), and human-associated ones including raccoons and opossums are
becoming increasingly detrimental to nesting beaches.
Poaching: In the U.S., killing of female turtles is infrequent. However, in
a number of areas, egg poaching and clandestine markets for eggs are not
uncommon. From 1983 to 1989, the Florida Marine Patrol, DEP, made 29
arrests for illegal possession of turtle eggs.
Management
Conservation efforts for the leatherback have greatly improved since it was
federally listed as endangered on June 2, 1970. During the 1970s, nest survey and
protection efforts were generally sporadic and did little to reduce the widespread
egg poaching on U.S. Caribbean beaches. Beginning in 1981, however, intensive
nest survey and protection efforts were initiated on the single most important
leatherback nesting beach in the U.S. Caribbean, Sandy Point, St. Croix. Prior to
this, the majority of the 150 to 350 nests deposited annually were lost to poaching
or erosion. Now overall hatch success exceeds 50 to 60 percent in most years.
The FWS, in cooperation with Earthwatch, initiated similar measures on the
other main U.S. Caribbean leatherback nesting beaches on Isla Culebra in 1984.
Prior to the intensive nighttime patrolling, a high percentage of the nests on this
island were poached. Overall hatch success is now greater than 75 percent in
most years. Nest survey and protection efforts occur on several other U.S.
Caribbean beaches of lesser but still significant importance such as Manchenil,
St. Croix, and Pinones, Humacao, and Luquillo beaches in Puerto Rico.
In Florida, leatherback nesting data are collected in conjunction with
loggerhead nesting surveys, which generally begin in early to mid-May. While a
portion of the leatherback nesting season is missed by the systematic loggerhead
and green sea turtle surveys, most nests are observed by someone and probably
reported because of intensive public use of the main leatherback nesting beaches
in Florida.
Along with the basic information on nest numbers, clutch size, and hatching
success, the Sandy Point and Culebra projects have included additional studies
of the nesting females and provided information on intra- and inter-nesting
frequency, movements, survivorship, turtle size and weight, diving behavior, prereproductive
migrations, nest temperature and expected hatchling sex ratio,
depredation rates, nest site selection, and embryonic deformities.
In 1982, 310 ha of land on Isla Culebra, including Playas Resaca and
Brava, were transferred to Culebra NWR. In 1984 the FWS purchased the 2.4
km long leatherback nesting beach at Sandy Point, St. Croix, establishing
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
Sandy Point NWR. These actions ensure the long-time protection of the most
important leatherback nesting beaches in the U.S. Virgin Islands and Puerto Rico,
although neither area is immune from external threats such as light pollution.
Recent reviews of sea turtle conservation efforts in the southeastern U.S.
appear in Hopkins-Murphy (1988) and Possardt (1991). In addition to
management of coastal habitats, NMFS and FWS (1992) discuss conservation
measures for the leatherback turtle in the marine environment. In the South
Florida Ecosystem, there are a number of management activities ongoing to
benefit the leatherback sea turtle.
Conservation of sea turtle nesting habitat is continuing on several NWRs in
South Florida, including Archie Carr, Hobe Sound, Ten Thousand Islands, and
the complex of satellite refuges in the Florida Keys. Acquisition of high-density
nesting beaches between Melbourne Beach and Wabasso Beach, Florida, is
continuing to complete the Archie Carr NWR. The State of Florida purchased the
first parcel specifically for the refuge in July 1990. Federal acquisition began in
1991. When completed, the refuge will protect up to 16 km of nesting beach.
Since the initial acquisition, Brevard County and the Richard King Mellon
Foundation have joined in as acquisition partners. Hobe Sound NWR, located
north of West Palm Beach in Martin County, contains 5.25 km of Atlantic coast
shoreline for nesting habitat. In addition to providing some of the most
productive sea turtle nesting habitat in the U.S., the refuge is also home to Florida
scrub-jays (Aphelocoma coerulescens) and gopher tortoises (Gopherus
polyphemus). The most longstanding beach management program has been to
reduce destruction of nests by natural predators, such as raccoons. Control of
numerous exotic plants such as Australian pine and Brazilian pepper (Schinus
terebinthifolius) are also major issues in managing the refuge.
One of the most difficult habitat protection efforts throughout South Florida
is trying to minimize or eliminate the construction of seawalls, riprap, groins,
sandbags, and improperly placed drift or sand fences. State and Federal laws
designed to protect the beach and dune habitat in South Florida include the
Coastal Barrier Resources Act of 1982 and the Coastal Zone Protection Act of
1985. These have had varying degrees of success at maintaining suitable nesting
sites for sea turtles. Prior to 1995, DEP permits were required for all coastal
armoring projects prior to construction. When issuing these permits, DEP
incorporated sea turtle protection measures, and sea turtle concerns were
generally well addressed.
However, in 1995, the Florida Legislature passed a law giving coastal
counties and municipalities the authority to approve construction of coastal
armoring during certain emergency situations. (All non-emergency armoring
situations must still receive an DEP permit prior to construction.) Although the
new law weakened prior regulations on armoring, it does require that emergency
armoring structures approved by a coastal county or municipality be temporary
and that the structure be removed or a permit application submitted to DEP for a
permanent rigid coastal structure within 60 days after the emergency installation
of the structure.
In addition, to implement this new law, DEP finalized a formal agency rule
on coastal armoring on September 12, 1996. The new rule recommends that local
governments obtain the necessary approval from the FWS prior to authorizing
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
armoring projects. The new rule also requires that several measures be
undertaken to address sea turtle concerns for non-emergency armoring and for
placement of permanent rigid coastal structures subsequent to an emergency
(temporary) armoring event. For example, the new regulations require that (1)
special conditions be placed on permitted activities to limit the nature, timing,
and sequence of construction, as well as address lighting concerns; (2) structures
not be used where the construction would result in a significant adverse impact,
and (3) armoring be removed if it is determined to not be effective or to be
causing a significant adverse impact to the beach and dune system.
Beach nourishment is a better alternative for sea turtles than seawalls and
jetties. When beach nourishment was done mostly in the summer, all nests had
to be moved from the beach prior to nourishment. Now FWS and State natural
resource agencies review beach nourishment projects to ensure appropriate
timing of nourishment during the nesting and hatching season. In southeast
Florida, the leatherback nesting and hatching season is from February 15 through
November 30. Any management decisions regarding beach nourishment, beach
armoring and other coastal construction, marina and dock development, and
artificial lighting should consider these dates. Beaches where compaction after
nourishment is a problem are plowed to a depth of 92 cm to soften the sand so
that it is useable for nesting turtles (Nelson and Dickerson 1987). Progress is
being made toward better timing of projects and sand quality.
Progress is being made by counties and cities to prevent disorientation and
misorientation of hatchlings due to artificial lighting (Ernest et al. 1987, Shoup
and Wolf 1987). In South Florida, lighting ordinances have been passed by
Indian River, St. Lucie, Martin, Palm Beach, Broward, Monroe, Collier,
Charlotte, Sarasota and Lee counties, as well as numerous municipalities. Most
recently, Witherington and Martin (1996) provide a thorough discussion of the
effects of light pollution on sea turtle nesting beaches and on juvenile and adult
turtles, and offer a variety of effective management solutions for ameliorating
this problem.
Information on the status and distribution of the leatherback sea turtle is
critical to its conservation. Monitoring the various life stages of the turtles on
nesting beaches is being conducted to evaluate current and past management
practices. Data are collected on the number of nests laid, the number of nests that
successfully hatch, and the production of hatchlings reaching the ocean.
Standardized ground surveys on index beaches are underway throughout Florida
by the FWS, DEP, and private groups and universities. Because of the turtles’
slow growth rates and subsequent delayed sexual maturity, all monitoring will
need to be conducted over a long period of time to establish population trends.
Mortality of leatherback turtles has been monitored since 1980 through the
implementation of a regional data collection effort. This voluntary stranding
network from Maine to Texas is coordinated by the NMFS and serves to
document the geographic and seasonal distribution of sea turtle mortality
(Schroeder 1987). Since 1987, four index zones have been systematically
surveyed. It is clear that strandings represent an absolute minimum mortality.
However, they can be used as an annual index to mortality and are an indication
of the size and distribution of turtles being killed. They can also provide valuable
biological information on food habits, reproductive condition, and sex ratios.
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LEATHERBACK SEA TURTLE Multi-Species Recovery Plan for South Florida
A substantial effort is being made by government and non-government
agencies and private individuals to increase public awareness of sea turtle
conservation issues. Federal and State agencies and private conservation
organizations, such as the Center for Marine Conservation, Greenpeace, and
National Audubon Society, have produced and distributed a variety of audiovisual
aids and printed materials about sea turtles. These include: a booklet on
the different types of light fixtures and ways of screening lights to lessen their
effects on hatchlings (Raymond 1984b), the brochure “Attention Beach Users”,
“Lights Out” bumper stickers and decals, a coloring book, video tapes,
slide/tape programs, full color identification posters of the various species of
sea turtles, and a leatherback poster. Florida Power and Light Company also
has produced a booklet (Van Meter 1990) and two leaflets with information on
sea turtles, as well as a coastal roadway lighting manual. Many beaches have
been posted with signs informing people of the laws protecting sea turtles and
providing either a local or a hotline number to report violations.

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