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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

species.

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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publication 420-529

2

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

serious consequences.

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

3

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

digging burrows.

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

previous years.

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

decades.

Turtles grow rapidly as juveniles

until they reach reproductive

maturity. Growth

4

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

except Antarctica

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

California.

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

5

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

Southeastern Asia.

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,

and plants.

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

nesting habitat.

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

Asia increases.

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

sea turtles.

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

6

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

them.

Turtle Web Links

Partners in Amphibian and Reptile Conservation

(PARC) Teacher Resources: http://www.parcplace.

org/education/index.htm

Reptiles and Amphibians of Virginia and Maryland:

http://mysite.verizon.net/vze1m6wp/

Georgia Reptiles: http://museum.nhm.uga.edu/

gawildlife/reptiles/reptiles.html

New Jersey Bog Turtle Slide Show: http://www.state.

nj.us/dep/fgw/slideshows/bogturtle/bogtrtintro.htm

Ohio Reptiles: http://www.dnr.state.oh.us/wildlife/

Resources/reptiles/reptiles.htm

Turtle Conservation Fund: http://www.biodiversityhotspots.

org/xp/Hotspots/home/news.xml

Distributions of World Turtles, The EMYSystem:

(http://emys.geo.orst.edu/

Habitat Management Guidelines for Amphibians and

Reptiles: http://herpcenter.ipfw.edu/parcmw.htm

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,

Okla.

Ernst, C.H., Lovich, J.E.,

and Barbour R.W. 1994.

Turtles of the United

States and Canada.

Smithsonian

Institution Press,

Washington, D.C.

Klemens, M.W. 2000. Turtle Conservation. Smithsonian

Institution Press, Washington, D.C.

Acknowledgements

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

Wildlife Service.

Art illustrations by Sally Bensusen, Mark Chorba,

and Mike Pinder.

Reviewed by Michelle Davis, research associate, Fisheries and Wildlife

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