Sustaining America's Aquatic Biodiversity
Turtle Biodiversity and Conservation
Joseph C. Mitchell, Department of Biology, University of Richmond, Richmond, Va.
Kurt A. Buhlmann, Conservation International, Center for Applied Biodiversity Science,Washington, D.C. Turtles are freshwater, marine, and terrestrial
vertebrates with a shell. There are about 300
living species worldwide in 12 families and
about 89 genera. Of these, eight species are marine,
49 are land, and about 250 are freshwater to semiaquatic.
The inexact numbers reflect changing taxonomy and
descriptions of new species. Forty-eight species occur
in the United States and Canada, with the highest
diversity in the Southeastern United States. Most of
these are freshwater species, including the wellknown
box turtles that are primarily terrestrial. Of
the remaining species, three are tortoises and five are
marine (sea) turtles.
Turtles are found worldwide except in the coldest
regions. Their diversity is greatest in the tropical and
lower temperate regions. They have colonized many
habitats from deserts (several tortoises), forests,
wetlands, ponds, and rivers (freshwater species) to the
oceans (sea turtles).
Many species of turtles worldwide and in the United
States are in need of conservation and some are close
to extinction, particularly in Asia. The primary threats
to turtles are habitat loss, alteration, and fragmentation;
mortality from road traffic, urban predators such
as raccoons and introduced species; and the collection
of wild turtles for the commercial pet trade and
oriental food markets. Throughout the world, many
people eat turtles and/or their eggs. The demand for
turtles of all kinds in the oriental food markets, especially
in China, is driving many species to the brink of
extinction. Environmental and landscape changes in
North America threaten many populations. Pollution
(e.g., contamination by pesticides) is known to disrupt
endocrine function and cause sex reversal in some
Turtles are some of the longest-lived vertebrates.
Among the reptiles, turtles, crocodilians, and some of
the large snakes are longer-lived than most lizards and
small snakes. In studies of North American freshwater
turtles, Blanding's turtle appears to be one of
the longer lived species, as individuals older than 55
years are known to be reproductive. The oldest known
age for painted turtles in a Michigan population was
34 years old. Yellow-bellied slider turtles and eastern
mud turtles in South Carolina were both estimated
to live for about 35 years. The fact that most turtles
are long-lived, with most living for several decades
and some known to live as long as a century, makes it
difficult for these unique animals to sustain losses of
individuals from populations.
A primary reason why many tortoise and freshwater
turtles are endangered is their life history strategy.
They take a long time to reach sexual maturity (i.e.,
some species require 20 years). This is in sharp conwww.
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trast to traditionally-hunted North American wildlife
species such as rabbits or white-tailed deer that can
reproduce at six months to one year of age; these animals
may only live to be 2 or 3 years old. Conversely,
turtles spend their juvenile years building hard shells
that will enable them to survive for many years;
perhaps a century for a few species, such as the giant
tortoises of the Galapagos Islands.
Eastern box turtles, for example,
possess a life history much
like humans; they reach
maturity in their teens,
produce few offspring,
and live for
decades. The significant
differences are that in turtles
there is no known curtailment of the ability to reproduce
and egg and juvenile mortality is high. Thus,
loss of the older individuals in a population causes
major negative effects. Many box turtles are killed
on roads annually and many are collected for the pet
trade. Consider that this and other species cannot
withstand losses of adults and one will realize that the
killing and removal of even one old individual has
Conservation efforts on behalf of turtles include
protecting habitat, controlling or preventing collecting,
and reducing mortality through management of
habitats and predators. Some efforts are local, some
are national, and others are international. The list of
resources at the end of this publication provides a
window into these activities.
What Is a Turtle?
No one mistakes a turtle for anything else. One sees
them basking on logs in lakes and ponds, walking in
the forest or other terrestrial habitats, or nesting on
beaches along the shoreline. Some species are secretive
and seldom seen. Turtles are incredibly diverse.
They come in all shapes and sizes, and each species
is unique. The massive sea turtles have limbs that
are modified to resemble paddles. They can, and do,
travel across an entire ocean, but have great difficulty
hauling themselves up on an ocean beach to dig a
nest. At the opposite end of the spectrum are the land
tortoises which have club-like feet that resembling
those possessed by elephants. Tortoises may drown if
they fall into water over their heads.
Most freshwater turtles, including the ubiquitous
box turtle, have limbs modified to allow for both
swimming and walking. However, variation within
freshwater turtles is still great. The soft-shell turtles
are fast and powerful swimmers, the snapping and
musk turtles, often called 'stinkpots,' are underwater
'bottom walkers,' while the colorful spotted turtle is
confined to shallow wetlands.
All turtles are included in the Order
Testudines. Modifications of the unique
shell and other body parts characterize
each of the 12 families worldwide. Of these,
seven families occur in North America.
They include sea turtles, tortoises, softshell
turtles, snapping turtles, box turtles,
map turtles, mud turtles, cooters, sliders,
and painted turtles, among others.
All turtles lay shelled eggs. Most deposit them in
nests constructed in the ground by the female parent
and a few lay eggs in leaf litter and on stumps in
wetlands. Most turtle species (and all crocodilians)
possess temperature-dependent sex determination
(TSD); the sex of the baby turtle is determined by
nest temperatures at a sensitive time during embryonic
development. There are no sex chromosomes as
in most other vertebrates.
Structure and appearance
The distinctive shell is the most unique feature of turtles.
The leatherback sea turtle has the largest known
shell with a length of over six feet. Turtle body armor
is made up of 59 to 61 dermal bones organized into an
upper part (carapace) and lower part (plastron) of the
shell that are connected together by extensions (bridges)
of the plastron. Many bones (ribs, vertebrae, and
sternum) are modified and expanded to form the shell.
Another unique aspect of turtles is that the pectoral
and pelvic girdles are positioned inside the rib cage
(shell); they are outside in all other vertebrates. This
body plan has been in existence for over 200 million
years, and has served turtles well, until now. Other
features include a sharp-edged beak without teeth,
hard, keratinized (fingernail-like) plates that overlap
the bony shell, and the ability of some species to pull
their heads and necks inside the protective shell.
Sea turtles are the largest of the North American
turtles. Their forelimbs are modified into flippers and
rear limbs are formed as paddles. Freshwater turtles
in the Family Emydidae all have hard shells and are
highly variable in color and pattern. They include
the largest freshwater turtles, the snapping turtles
that have large heads, massive jaws, sharp claws on
powerful limbs, and flexible shells. Mud and musk
turtles in the Family Kinosternidae are small, relatively
drab species with dark shells and skin and scent
glands that produce foul-smelling odors in some species.
Soft-shell turtles lack the hard shell and instead
have a flexible, leathery skin covering a reduced bony
structure. These highly aquatic species have long
necks and powerful limbs with expanded feet for
swimming fast. Tortoises have hard, relatively highdomed
shells, rear feet modified like elephant's feet
for walking, and wide forelimbs and toes designed for
Hatchlings and juveniles of all species have soft
shells compared to adults because the bones take
months to years to harden. The young of some Asian
species have spines along the margins of their shells
at hatching that may serve to protect the turtles until
the shells harden.
What do they eat?
Turtle diets vary widely. Some are strict herbivores,
others are herbivorous as adults but carnivorous as
juveniles, some are entirely carnivorous, and others
are strictly omnivorous. Strict herbivores include tortoises
and the green sea turtle. Those that switch from
animal prey as juveniles to plants as adults include
river cooters, red-bellied turtles, and red-eared sliders.
Strict carnivores include leatherback sea turtles (they
prefer jellyfish), loggerhead sea turtles (crabs), chicken
turtles (crayfish, other invertebrates, insect larvae),
map turtles (mussels), mud and musk turtles (snails,
mussels), soft-shell turtles (invertebrates, fish), and
juvenile alligator snapping turtles (small fish caught
by 'luring' them with a worm-like tongue). Surprisingly,
the adult alligator snapping turtle is an omnivore,
scavenging dead fish but also consuming acorns
that float on the water surface in the fall. Turtles that
eat both animal prey and plants as adults and juveniles
include common snapping turtles, box turtles, painted
turtles, and spotted turtles. Box turtles eat slugs, carrion,
fruits, berries, and leafy plants. The estuarine
diamondback terrapin specializes on snails and clams.
How do they reproduce (life cycle)?
Adults of most species (e.g., painted turtles, cooters,
sliders) engage in elaborate courtship rituals, although
some, such as mud and musk turtles, have relatively
simple mating rituals. Fertilization is internal. Females
of small species lay one to ten eggs, mediumsized
females lay ten to 30 eggs, snapping turtles can
lay 75 eggs, and sea turtles can lay up to 200 eggs
in each nest. Sea turtle females may deposit several
clutches in a single season but most turtles will
lay only one clutch in a year. Many will skip years
between reproduction depending on food resources in
Most species in North America lay eggs in late spring
and embryos develop within the eggs for about 60 to
90 days. Hatchlings of some species emerge immediately
from the nest once they hatch from the egg.
However, hatchings of other species (often painted
turtles, chicken turtles, and red-bellied cooters)
remain in the nest after hatching, sometimes over an
entire winter, to emerge the following spring at a presumably
more favorable time. Hatchlings of painted
turtles in the north are able tolerate subzero temperatures
and being partially frozen. Hatchlings of sea
turtles are well known for their synchronous hatching
and mad dash for the sea, usually in August or
September of the same year the eggs were laid. Other
species that do not overwinter in the nest include
snapping turtles, musk turtles, and bog turtles.
How long do they live?
Turtles live long lives. The oldest documented is
an Aldabra tortoise caught as an adult and held in
captivity for 152 years until its accidental death.
Documented ages for eastern box turtles are over 100
years in the wild, and up to 75 years for Blanding's
turtles and 60 years for alligator snapping turtles and
wood turtles. Most species of freshwater
turtles live for at least several
Turtles grow rapidly as juveniles
until they reach reproductive
then slows down, although individuals are capable
of growing each year until they die. One can often
determine the age of a juvenile turtle by counting the
growth rings (annuli) on the shell, similar to looking
at rings on a tree trunk. Turtles of all species, however,
exhibit years of no or limited growth, especially
once they reach maturity. The growth rings on older
individuals are too close together to count, thus this
method is accurate only for the first four to five years
of growth, but occasionally more in some species.
Distribution and Diversity
Turtles occur in temperate and
tropical regions on all continents
and in all the major oceans.
Tortoises and freshwater
turtles are found in seven major regions of the world.
Ordered by species richness, they include: Asia (90),
South America (61), North America (48), Africa (45),
Meso-America (35), Australia (26), and the Mediterranean
Region (10). Some species occur in more
than one region and are thus counted more than once.
Centers of biodiversity for turtles are in Southeastern
Asia, the Southeastern United States, Central America,
the Amazon Basin, and Eastern Australia.
Most species in North America occur in the Southeastern
states from east-central Texas eastward to
the Atlantic states, with several species extending
their ranges well into New England and southern
Canada. Tortoises inhabit deserts of the Southwest
and dry, sandy areas of the Southeast from southern
South Carolina to the northern edge of the Florida
Everglades. Most of the freshwater pond and river
turtles occur in the eastern and midwestern portions
of the continent with two species reaching the West
Coast. Mud and musk turtles occur primarily in the
Southeast and extend into Central America. Soft-shell
turtles are primarily found in the Southeast and Midwest,
but occur up the Rio Grande into New Mexico
and have been introduced into the lower Colorado
River. The diamondback terrapin occurs only in salt
marshes along the Gulf and Atlantic coasts from near
Corpus Christi, Texas, to Cape Cod, Massachusetts.
Sea turtles occur along the Atlantic Coast as far north
as New England, although the leatherback has been
seen as far north as Nova Scotia. Sea turtles seldom
occur along the rocky Pacific Coast except in Baja
Where do they live?
Different habitats support different species of turtles.
Sea turtles are exclusively marine and estuarine
except when females come ashore to lay eggs. Juveniles
of three species along the Atlantic Coast spend
summers in the Chesapeake Bay and one makes
it up to Long Island. Diamondback terrapins occur
only in estuaries and coastal bays with brackish
water. Large lakes and ponds support cooters, sliders,
snapping turtles, painted turtles, and musk
turtles. Large rivers support
river cooters, softshells, map
turtles, musk turtles, and the
alligator snapping turtle.
Smaller streams in the Northeast
support wood turtles. Mud, spotted,
bog, and wood turtles occupy shallow
freshwater marshes and marsh-like
systems along streams. Few species occur in mountainous
areas, although the eastern box turtle occurs
at over 5,000 feet elevation, and the bog turtle is
found in mountain seeps at mid-elevations in the Blue
Ridge Mountains. Large vernal pools and most Carolina
bays support populations of painted, chicken, and
mud turtles, sliders, and snapping turtles. Box turtles
occupy hardwood forests, open grasslands, and agricultural
areas. Gopher tortoises occur in the Southeastern
United States pinelands where the soil is dry
and sandy, and desert tortoises occur in the Mojave
and Sonoran deserts.
What Good Are They?
Turtles, tortoises, and sea turtles play many important
roles on the ecological stage. As consumers of plants
and other animals they are links to the energetic
webs in aquatic and terrestrial ecosystems. As prey
of other animals (as eggs, juveniles, and adults), they
are sources of energy to other links in the food web.
Movements of turtles among wetlands and between
wetlands and terrestrial habitats, especially to lay
eggs in terrestrial nests, results in a major energy
transfer link between these two ecological systems.
The loss of any turtle species, each of which represents
over 200 million years of evolution, persistence,
and genetic information, would create a void that can
never be filled by other species.
As long-lived vertebrates, they are studied to learn
how animals have evolved to cope with uncertainty
in a wide variety of environments. Turtles are models
for the study of longevity, and may show us how to
reduce senility and prolong human life. In some developing
countries, turtles provide important sources
of protein and economic stability, although hunting
wild turtles has created a major conservation crisis in
Turtles have been included in the mythologies of
many ancient cultures. In a Hindu myth, the earth is
a hemisphere resting flat side down on the backs of
four elephants standing on the back of a giant tortoise.
North American Indians included turtles in their
myths and in their daily lives, mostly as food, implements,
and ritual objects. Various forms of art have
used turtles as their subjects. Turtles have ecological
values in natural systems, and they also provide cultural,
artistic, and spiritual inspiration values.
Like all species with which we inhabit the earth, we
sometimes have a difficult time justifying why turtles
are unequivocally important to humans. However,
if we consider turtles as rivets on the wing of an
airplane, we might pop out a few rivets with no ill
effects, but if we pop out enough rivets, eventually a
wing will fall off. If too many animal species become
extinct, the natural ecosystem that supports life on
Earth will crash, perhaps bringing humans down with
it. Protecting turtle habitat will undoubtedly help to
protect ecosystems and other forms of life, animals,
Threats to Turtles
Habitat loss and exploitation for food
markets are the most important
threats to turtles worldwide. Loss
of freshwater wetlands, hardwood
forests, longleaf pine forests, and
nesting beaches along coastlines
and rivers have caused population losses
worldwide. Conversion of desert or scrub
lands to agricultural fields and monocultures
reduces habitat for tortoises. Channelization of
streams and rivers causes loss of critical basking and
Several species spend parts of their annual life cycles
in freshwater and the rest of the time on land usually
buried in the substrate. Mud and chicken turtles, for
instance, spend months, including winters, buried on
land. Forested uplands connected to wetlands are very
important habitats for turtles and other animals that
need and use both land and water habitats. Individuals
of most species occasionally wander away from their
home wetland and move long distances to other wetlands.
The habitats that connect these distant wetlands
are corridors for migrating turtles. Highways, housing
developments, and forest clear cuts are roadblocks
and deathtraps for turtles and other wildlife trying
to migrate to other wetlands. Female turtles of some
species, like the Blanding's turtle, move over a mile
to find suitable nest sites.
Hunting and collecting wild turtles for food markets
in Southeast Asia and the pet trade worldwide threaten
most species with extinction. Laws in the United
States and Canada prevent the commercialization of
turtles, and yet turtles are still being shipped to Asia
for food. Pressure on turtle populations in the United
States are expected to grow as demand in Southeast
Commercial fisheries, including long-line and drift
gill nets in the open ocean and fish traps and shrimp
trawl nets in shallow seas have severely reduced
sea turtle populations. By-catch (accidental catch of
non-target species) in fish nets, trawls, and traps is the
most important cause for the decline of leatherback
Respiratory diseases in desert and gopher tortoises in
North America have caused population die-offs and
declines. Such an infection resulted in the addition of
the Mojave Desert tortoise population to the federal
list of threatened species. Swollen neck abscesses in
the eastern box turtle has been correlated with
pesticide pollution. Severe malformations
of the turtle shell have been
related to industrial pollution.
The introduction of exotic wetland
plants, such as phragmites and
purple loosestrife, that have out-competed
native aquatic plants, has reduced
natural turtle habitat nationwide. The bog turtle has
lost much of its native habitat because of foreign
invasive wetland plants and is now on the federal list
of endangered species.
Urbanization and suburbanization have reduced
natural turtle habitat and created good environments
for turtle predators The most notorious turtle predator
is the raccoon, which eats turtle eggs and adults.
Raccoon populations in urban areas have increased
because of garbage and artificial feeding and the
elimination of raccoon predators. Highway traffic is
responsible for the loss of thousands of turtles, especially
box turtles, annually in the United States.
What Can You Do?
Everyone should be aware of the plight of turtles
worldwide, and learn of conservation activities,
including local and state laws regulating turtle trade.
Make sure that the turtles in your pet store are legally
caught and sold. Report any suspicious activities to
the proper authorities.
Help prevent the loss of habitat, especially wetlands
and the adjacent uplands. Participate in local land-use
planning, and help to ensure that wetlands and riparian
areas are set aside and protected. Remember that
the adjacent uplands are as important for some turtles
as the wetlands they inhabit. Participate in habitat restoration
projects. Learn more about turtle conservation
and always take the opportunity to educate others
about the plight of these unique animals.
Turtles are one of the most ancient and unique of all
aquatic animals that have survived through evolutionary
time. Because they are still with us, we sometimes
take them for granted. However, if they only existed
as fossils in museums, we might view their unusual
protective bony shell with wonder. Turtles stimulate
appreciation for nature in young people. Future
human generations would be impoverished without
Turtle Web Links
Partners in Amphibian and Reptile Conservation
(PARC) Teacher Resources: http://www.parcplace.
Reptiles and Amphibians of Virginia and Maryland:
Georgia Reptiles: http://museum.nhm.uga.edu/
New Jersey Bog Turtle Slide Show: http://www.state.
Ohio Reptiles: http://www.dnr.state.oh.us/wildlife/
Turtle Conservation Fund: http://www.biodiversityhotspots.
Distributions of World Turtles, The EMYSystem:
Habitat Management Guidelines for Amphibians and
Selected Books and Publications
Buhlmann, K.A., Hudson, R., and Rhodin, A.G.J.
2002. A Global Action Plan for Conservation of
Tortoises and Freshwater Turtles: Strategy and Funding
Prospectus 2002-2007. The Turtle Conservation
Fund. Washington D.C. Conservation International
and Chelonian Research Foundation, 30 pp.
Dodd, C.K., Jr. 2001. North American Box Turtles, A
Natural History. University of Oklahoma Press, Norman,
Ernst, C.H., Lovich, J.E.,
and Barbour R.W. 1994.
Turtles of the United
States and Canada.
Klemens, M.W. 2000. Turtle Conservation. Smithsonian
Institution Press, Washington, D.C.
We greatly appreciate the editorial review of Nancy
Templeman, Virginia Cooperative Extension, and the
support of Randy Rutan and Hilary Chapman, National
Conservation Training Center, U.S. Fish and
Art illustrations by Sally Bensusen, Mark Chorba,
and Mike Pinder.
Reviewed by Michelle Davis, research associate, Fisheries and Wildlife
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