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Imperiled Amphibians and Reptiles - Reptiles

species turtle habitat sea

Approximately 6,300 species of reptiles have been described. These include turtles, snakes, lizards, and crocodilians. Birds are also technically reptiles (birds and crocodiles are actually close relatives), but have historically been treated separately. Reptiles differ from amphibians in that their skin is cornified—that is, made of dead cells. All reptiles obtain oxygen from the air using lungs. Most reptiles lay shelled eggs, although many species, particularly lizards and snakes, give birth to live young.

Many reptiles are in serious decline. Numerous species are endangered due to habitat loss or degradation. In addition, humans hunt some reptiles for their skins, shells, or meat. Global climate change has affected some reptile species, particularly turtles, in ominous ways—this is because in some reptiles, ambient temperatures determine whether males or females are produced, in some cases resulting in few or no males being born. Natural disasters may also affect reptiles, as in 1999, when tens of thousands of turtle hatchlings were lost to the fury of Hurricane Floyd.

There are 78 reptiles listed as endangered, including 14 U.S. species and 64 foreign species. An additional 37 species are listed as threatened, including 22 U.S. species and 15 foreign species. Threatened and endangered U.S. reptiles are listed in Table 6.3.

Sea Turtles

Sea turtles are excellent swimmers and spend nearly their entire lives in water. They feed on a wide array of food items, including mollusks, vegetation, and crustaceans. Some sea turtles are migratory, swimming thousands of miles between feeding and nesting areas. Individuals are exposed to a variety of both natural and human threats. Because of these, only an estimated one in 10,000 sea turtles survives to adulthood.

Of the seven species of sea turtles that exist worldwide, six spend part or all of their lives in U.S. territorial waters—the loggerhead turtle, green turtle, leatherback turtle, hawks-bill turtle, olive ridley turtle, and Kemp's ridley turtle. (The seventh species, the flatback turtle, occurs near Australia.) All are listed by the Fish and Wildlife Service as either threatened or endangered. Figure 6.4 shows leatherback turtle population trends at nesting grounds in St. Croix, Virgin Islands, over the last several decades. Conservation efforts for this species have met with some success.

THREATS TO NESTING TURTLES.

Sea turtles bury their eggs in nests on sandy beaches. The building of beach-front resorts and homes has destroyed a large proportion of nesting habitat. Artificial lighting associated with coastal development also poses a problem—lights discourage females from nesting and also cause hatchlings to become disoriented and wander inland instead of out to sea. Finally, beach nourishment, the practice of rebuilding eroded beach soil, creates unusually compacted sand on which turtles are unable to nest. The sands of Tortuguero National Park in Costa Rica are believed to be the last remaining nesting ground for one species, the endangered green turtle.

SHRIMP-NET CASUALTIES.

Large numbers of sea turtles are killed in shrimp nets in the Gulf of Mexico and the Caribbean. In 1990 the National Academy of Sciences reported that shrimp trawling was the greatest cause of sea turtle deaths in U.S. waters, killing 55,000 turtles every year. In 1981 the turtle excluder device (TED), which allows sea turtles to escape from shrimp nets, was invented.

TABLE 6.3
Endangered or threatened reptiles, February 2004

Status Species name
T(S/A) Alligator, American (Alligator mississippiensis)
E Anole, Culebra Island giant (Anolis roosevelti)
T Boa, Mona (Epicrates monensis monensis)
E Boa, Puerto Rican (Epicrates inornatus)
E Boa, Virgin Islands tree (Epicrates monensis granti)
E Cooter (=turtle), northern redbelly (=Plymouth) (Pseudemys rubriventris bangsi)
E Crocodile, American (Crocodylus acutus)
E Gecko, Monito (Sphaerodactylus micropithecus)
T Iguana, Mona ground (Cyclura stejnegeri)
E Lizard, blunt-nosed leopard (Gambelia silus)
T Lizard, Coachella Valley fringe-toed (Uma inornata)
T Lizard, island night (Xantusia riversiana)
E Lizard, St. Croix ground (Ameiva polops)
T Rattlesnake, New Mexican ridge-nosed (Crotalus willardi obscurus)
E, T Sea turtle, green (Chelonia mydas)
E Sea turtle, hawksbill (Eretmochelys imbricata)
E Sea turtle, Kemp's ridley (Lepidochelys kempii)
E Sea turtle, leatherback (Dermochelys coriacea)
T Sea turtle, loggerhead (Caretta caretta)
T Sea turtle, olive ridley (Lepidochelys olivacea)
T Skink, bluetail mole (Eumeces egregius lividus)
T Skink, sand (Neoseps reynoldsi)
T Snake, Atlantic salt marsh (Nerodia clarkii taeniata)
T Snake, Concho water (Nerodia paucimaculata)
T Snake, copperbelly water (Nerodia erythrogaster neglecta)
T Snake, eastern indigo (Drymarchon corais couperi)
T Snake, giant garter (Thamnophis gigas)
T Snake, Lake Erie water (Nerodia sipedon insularum)
E Snake, San Francisco garter (Thamnophis sirtalis tetrataenia)
T(S/A), T Tortoise, desert (Gopherus agassizii)
T Tortoise, gopher (Gopherus polyphemus)
E Turtle, Alabama redbelly (Pseudemys alabamensis)
T(S/A), T Turtle, bog (=Muhlenberg) (Clemmys muhlenbergii)
T Turtle, flattened musk (Sternotherus depressus)
T Turtle, ringed map (Graptemys oculifera)
T Turtle, yellow-blotched map (Graptemys flavimaculata)
T Whipsnake (=striped racer), Alameda (Masticophis lateralis euryxanthus)
E = Endangered
T = Threatened
T(SA) = Similarity of appearance to a threatened taxon
SOURCE: Adapted from "U.S. Listed Vertebrate Animal Species Report by Taxonomic Group as of 02/17/2004," Threatened and Endangered Species System (TESS), U.S. Fish and Wildlife Service, Washington, DC, 2004 [Online] http://ecos.fws.gov/tess_public/TESSWebpageVipListed?code=V&listings=0#E [accessed February 17, 2004]

The use of TEDs became a requirement under the Endangered Species Act. Biologists attribute the gradual increase in some turtle species in the 1990s to the use of TEDs. In January 1996 federal courts ruled that, under provisions of the Endangered Species Act, the Commerce Department must require all nations that export shrimp to the United States to use TEDs as well.

In April 1998 the World Trade Organization (WTO), an international trade body, ruled that the United States could not prohibit shrimp imports from countries that do not use turtle excluder devices. Experts fear that when free trade conflicts with environmental protection, the WTO is likely to favor trade over environmental protection. In addition, the law requiring TEDs be used by countries that export shrimp to the United States has been FIGURE 6.4
Number of leatherback turtles and leatherback remigrants returning to nesting grounds at Sandy Point, St. Croix, U.S. Virgin Islands, 1981–97
suspended by the Bush administration, under the assumption that it would hurt commerce

KEMP'S RIDLEY TURTLE.

Kemp's ridley turtle is the smallest sea turtle, with individuals measuring some three feet in length and weighing less than 100 pounds. Kemp's ridley is also the most endangered of the sea turtle species. It has only one major nesting site, located in Rancho Nuevo, Mexico, where it faces increasing threats from human activity. In particular, eggs and hatched juveniles are collected by people or eaten by coyotes. At Rancho Nuevo, numerous female Kemp's ridley turtles nest at the same time—this is referred to as an "arribada." Female ridleys nest in daylight, unlike other sea turtle species. Kemp's ridley populations have declined drastically over the past several decades—in 1947, approximately 42,000 females nested in one day. In 1990, only 300 females were observed. Since then, Kemp's ridley numbers have improved a little, with approximately 900 females tallied in Mexico in 1999.

The decline of the Kemp's ridley turtle is due primarily to human activities such as egg collecting, fishing for juveniles and adults, and killing of adults for meat or other products. In addition, Kemp's ridleys have been subject to high levels of incidental take by shrimp trawlers. They are also affected by pollution from oil wells, and by floating debris in the Gulf of Mexico, which can choke or entangle turtles. Now under strict protection, the population appears to be in the earliest stages of recovery, with numbers having increased annually for several years. Population increase can be attributed to two primary factors—full protection of nesting females and their nests in Rancho Nuevo, and TED requirements for shrimp trawlers in the U.S. and Mexican waters. Prior to TED requirements, shrimp boats killed 500 to 5,000 Kemp's ridleys each year. Responsibility for conservation of the Kemp's ridley turtle is shared by the Fish and Wildlife Service and the National Marine Fisheries Service because turtles nest on land but otherwise live in the ocean.

In the late 1970s, biologists attempted to establish a second nesting site for Kemp's ridleys on the Padre Island National Seashore in Texas. In 2001, eight Kemp's ridley nests were found there. Padre Island is also the site of a captive breeding program for Kemp's ridleys—eggs are collected from nests and raised in a protected environment. After hatching, baby turtles are returned to the sea. This allows turtle hatchlings to bypass one of the most dangerous parts of the life cycle—approximately 85 percent of hatchlings survive incubation at the station, whereas only 17 percent survive in unprotected nests. In 2001, 656 eggs were incubated at the Padre Island Station, and several hundred turtles released. In 2002, a record 23 nests were found, and about 1,887 hatchlings were ultimately released in the fall of 2002.

However, in 2002, the National Park Service issued permits to BNP Petroleum for drilling gas wells in Padre Island's seaside dunes. The Sierra Club filed a lawsuit against the Fish and Wildlife Service, the National Park Service, and Secretary of the Interior Gale Norton for failing to adequately assess the impact of drilling on Kemp's ridley.

FIGURE 6.5
The desert tortoise is threatened due to habitat destruction, livestock grazing, invasion of non-native plant species, collection, and predation by ravens. (U.S. Fish and Wildlife Service)

Desert Tortoise

The desert tortoise (see Figure 6.5) was listed in 1990 as threatened in most of its range in the Mojave and Sonoran Deserts in California, Arizona, Nevada, and Utah. Decline of this species has resulted from collection by humans, predation of young turtles by ravens, off-road vehicles, invasive plant species, and habitat destruction due to development for agriculture, mining, and livestock grazing. Livestock grazing is particularly harmful to tortoises because it results in competition for food, as well as the trampling of young tortoises, eggs, or tortoise burrows. Invasive plant species have caused declines in the native plants that serve as food for tortoises. Off-road vehicles destroy vegetation and sometimes hit tortoises.

Desert tortoise populations are constrained by the fact that females do not reproduce until they are 15 to 20 years of age (individuals can live 80–100 years), and by small clutch sizes, with only 3–14 eggs per clutch. Juvenile mortality is also extremely high, with only 2 to 3 percent surviving to adulthood. About half this mortality is due to predation by ravens, whose populations in the desert tortoise's habitat have increased with increasing urbanization of desert areas—human garbage provides food for ravens and power lines provide perches.

Protected habitat for the desert tortoise includes areas within Joshua Tree National Park and Lake Mead National Recreation Area in Nevada and Arizona. There is also a Desert Tortoise Research Natural Area on a Bureau of Land Management habitat in California. A Habitat Conservation Plan for the area around Las Vegas requires developers to pay fees for tortoise conservation.

Snakes and Lizards

There are approximately 2,400 species of snakes and 3,800 species of lizards. Although they represent the largest group of reptiles, snakes and lizards are also among the least studied. There are numerous groups of lizards, including iguanas, chameleons, geckos, and horned lizards, among many others. There are even "flying" lizards found in the tropical forests of Southeast Asia—these are not capable of true flight, like birds and bats, but actually glide with "wings" formed by skin stretched over mobile and elongated ribs. Most lizards are carnivorous, although there are some herbivorous species as well, including the iguanas. Snakes are elongate reptiles that have, during the course of evolution, lost their limbs. All species are carnivorous. Most snakes are adapted to eating relatively large prey items, and have highly mobile jaws that allow them to swallow large prey. In some species, the jaw can be unhinged to accommodate prey. Several groups of snakes are also characterized by a poisonous venom which they use to kill prey.

In 2004 there were 12 U.S. snakes and 9 U.S. lizards listed as threatened or endangered.

SAN FRANCISCO GARTER SNAKE.

The San Francisco garter snake is one of the most endangered reptiles in the United States. It was one of the first species to be listed under the Endangered Species Act. The decline of this species can be attributed primarily to habitat loss resulting from urbanization. Most of the snake's habitat was lost when the Skyline Ponds, located along Skyline Boulevard south of San Francisco County along the San Andreas Fault, were drained in 1966 for development. In addition, the building of the San Francisco International Airport and the Bay Area Rapid Transit regional commuter network destroyed additional snake habitat. Pollution and illegal collection have also contributed to the species' decline. Most San Francisco garter snakes today inhabit areas in San Mateo County, south of San Francisco. The species lives close to streams or ponds and feeds mainly on frogs, including Pacific tree frogs, small bullfrogs, and California red-legged frogs, which are also endangered.

LAKE ERIE WATERSNAKE.

The Lake Erie watersnake inhabits portions of the Ohio mainland, as well as several small islands in Lake Erie. Its population has declined due primarily to habitat loss and human persecution, among other factors. Table 6.4 summarizes the sources of stress on Lake Erie watersnake populations, as well as the severity of stress and restoration feasibility. Historical and current ranges for the species are described in Figure 6.6. The Lake Erie watersnake is now extinct on three islands that it previously inhabited. The species was listed as threatened in 1999, and a recovery plan was completed by the Fish and Wildlife Service in September 2003.

MONITO GECKO.

The endangered Monito gecko is a small lizard less than two inches long. This species exists only on the 38-acre Monito Island off the Puerto Rican coast. Endangerment of the Monito gecko has resulted from human activity and habitat destruction. After World War II the U.S. military used Monito Island as a site for bombing exercises, causing large-scale habitat destruction. The military also introduced predatory rats, which

TABLE 6.4
Threats to the Lake Erie watersnake

Stress Source of stress Severity Restoration feasibility Score
Mortality intentional human-induced killing high medium 5
Hibernation habitat alteration interior island development—homes, roads, commercial development medium low 5
Summer habitat alteration shoreline development—construction of docks, marinas, erosion protection, etc. low low 4
Summer habitat degradation incompatible shoreline management practices low medium 3
Habitat loss weather events low low 4
Mortality weather events low low 4
Mortality roadkill low medium 3
Note: Threats were scored based on level of severity and feasibility of restoration. The score of the stress increases as severity increases and restoration feasibility decreases. Scores for secerity are as follows: low = 1; medium = 2; high = 3. Scores for restoration feasibility are as follows: low = 3; medium = 2; high = 1. Scores are achieved by adding the value of the severity and restoration feasibility columns. A score of 6 represents the most severe threat, while 2 represents the least severe threat.
SOURCE: "Table 2. Assessment of Threats to the Lake Erie Watersnake," in Lake Erie Watersnake Recovery Plan (Nerodia sipedon insularum), U.S. Fish & Wildlife Service, Great Lakes-Big Rivers Region (Region 3), Fort Snelling, MN, September 2003

FIGURE 6.6
Historic range of the Lake Erie watersnake on western basin Lake Erie islands

eat gecko eggs. In 1982 the FWS observed only 24 Monito geckos on Monito Island. In 1985 Monito Island was designated critical habitat for the species. The Commonwealth of Puerto Rico is now managing the island for the gecko and as a refuge for seabirds; unauthorized human visitation is prohibited.

FIGURE 6.7
Once abundant across Texas, the Texas horned lizard has disappeared from much of its habitat. (Corbis Corporation. Reproduced by permission.)

MONITOR LIZARDS.

In contrast to the Monito gecko, monitor lizards are among the largest lizard species in existence. The Komodo dragon, native to only a few islands in Indonesia, is the world's largest lizard. It reaches lengths of as much as ten feet and weighs as much as 300 pounds. Despite the fact that the Komodo dragon is protected under Appendix I of the CITES treaty, one of the greatest threats to this species is illegal trade. The price on delivery is approximately $30,000 for one Komodo dragon specimen.

Gray's monitor, a species found in forested low mountain habitats on the Philippine Islands, is also prized in illegal trade. Gray's monitor is also protected under CITES Appendix I.

HORNED LIZARDS (HORNY TOADS).

Horned lizards, sometimes called "horny toads," are native to the deserts of North America. There are 14 species of horned lizards. All species have flat, broad torsos and spiny scales and feed largely on ants. Although all horned lizards are reptiles, they are often referred to as horny toads because they bear some resemblance to toads in size and shape.

The Texas horned lizard (see Figure 6.7) was once abundant in the state of Texas and was designated the official state reptile in 1992. It has declined largely as a result of pesticide pollution, the spread of invasive fire ants across the state, and habitat loss. It is protected by state law in Texas.

Crocodilians

There are 22 existing species of crocodilians, a group that includes crocodiles, alligators, caimans, and gavials. Crocodilians play a crucial role in their habitats. They control fish populations and also dig water holes, which are important to many species in times of drought. The disappearance of alligators and crocodiles has a profound effect on the biological communities these animals occupy.

FIGURE 6.8
Range of the American alligator (alligator mississippiensis)

Worldwide, 17 species of crocodilians are in serious danger of extinction. Illegal trade poses one of the greatest threats to crocodilians, despite CITES restrictions. Conservation efforts include enforcement of trade restrictions and habitat restoration. Captive breeding programs are also underway for several species.

The Chinese alligator is one of many species listed in CITES Appendix I. Unfortunately, this species is among those most prized by collectors, commanding a black market price of as much as $15,000. The false gavial, a crocodilian that grows to 13 feet in length and is native to Indonesia, sells for an estimated $5,000 per specimen. Like the Chinese alligator, the false gavial is protected under CITES Appendix I.

In the United States, the American alligator was once a threatened species but has now recovered enough to qualify for delisting. Figure 6.8 shows the range of the American alligator. The elusive and reclusive American crocodile, however, remains highly endangered. Less than 500 American crocodiles remain in Florida swamps.

Tuatara

The two-foot-long, lizard-like tuatara is sometimes called a living fossil, being the sole existing representative of a once diverse group. Tuataras are native to New Zealand and the Cook Strait. Like many other reptiles, tuataras are valued by collectors. They are protected by CITES under Appendix I.

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