Emys marmorata

Geographic Range

Western pond turtles (also known as Pacific pond turtles and Pacific mud turtles) are native to the west coast and are found from Baja California, Mexico north through Klickitat County, Washington. Within this region, there are two subspecies: northwestern pond turtles ( E. m. marmorata ) are found in areas north of the American River in California; southwestern pond turtles ( E. m. pallida ) are found in areas south of San Francisco. There are isolated inland populations in Washington, Oregon, California, Nevada and Idaho. It has been suggested that some of these isolated populations represent introductions through human transport, although there is no clear evidence for this.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Western pond turtles use both aquatic and terrestrial habitats. They are found in rivers, lakes, streams, ponds, wetlands, vernal pools, ephemeral creeks, reservoirs, agricultural ditches, estuaries, and brackish waters. Western pond turtles prefer areas that provide cover from predators, such as vegetation and algae, as well as basking sites for thermoregulation. Such cover also provides shelter when wintering. Western pond turtles are observed in aquatic habitats ranging from 1 to 40 degrees Celsius. Juveniles are found primarily in areas between 12 and 33 degrees Celsius, whereas adults are found between 10 and 17 degrees Celsius. Adults tend to favor deeper, slow moving water, whereas hatchlings search for slow and shallow water that is slightly warmer. Terrestrial habitats are used for wintering and consist usually of burrows in leaves and soil. Western pond turtles also lay their eggs in terrestrial habitats.They are rarely found at altitudes above 1500m.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• brackish water brackish water

• Wetlands
• marsh marsh
• swamp swamp

• Other Habitat Features
• suburban suburban
• agricultural agricultural
• riparian riparian
• estuarine estuarine

Physical Description

Western pond turtles are generally yellowish with dark blotches in the center of the plastron. There is marbled patterning throughout the body. The dorsal area is generally dark brown to olive. The shell tends to be low, wide, and smooth. Adult males have a larger head, pointier snout, thicker tail base, and a wider neck characterized by white and yellow on the chin and throat. Adult females tend to have a blunt snout, thinner tail base, and darker markings on the chin and throat. Western pond turtles have webbed feet. Hatchlings tend to have a longer tail, soft shell, and be a lighter brown; darkening as they age. They weigh approximately 5g at hatching and measure around 28 mm in shell length. The southern subspecies tends to grown only to 115 mm in shell length, northern subspecies reach 210 mm in shell length.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes colored or patterned differently
• sexes shaped differently

Development

Females deposit eggs in a nest they dig on land at night. After incubation, hatchlings leave the egg only if the temperature is below 81 degrees Fahrenheit. Hatchlings tends to be male if the incubation temperature was below 86 degrees Fahrenheit or female if the incubation temperature was above 86 degrees Fahrenheit). Hatchlings immediately return to the water and grow at a rate of 3.29 mm/month, .08 mm/month, .05 mm/month, and .04 mm/month during successive growth seasons. Growth is accompanied by darkening of the body and hardening of the shell. After about 8 years of growth, the rate slows as the turtles mature into adults. Growth rate depends on environmental factors such as water, temperature, and food abundance. Colder water and less food slows growth.

• Development - Life Cycle
• temperature sex determination

Reproduction

Western pond turtle males court females using their forelimbs to scratch the anterior edge the female’s carapace. This is followed by the female raising her posterior end, after which mating occurs. Due to the seclusive nature of these animals there is not much known about the mating process.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Western pond turtles mate from May through August, with most females laying eggs in alternating years. Although the average age of maturity is between 8 and 14 years of age, females in the southern subspecies occasionally reach maturity at an earlier age. Nests are built up to 402 m from the water with an average distance of 28 m and require at least 10 cm of soil. Hatching success rates are approximately 70%, as there is a high rate of nest predation and complete nest failure. Nests are generally found in flat areas with low vegetation and dry, hard soil. Incubation takes approximately 3 months, with most hatchlings staying in the nest chamber until the following spring. Some hatchlings in southern and central California emerge in the fall.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

After the eggs are laid, there is no evidence of parental care.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

As hatchlings, western pond turtles are easy prey and have a survival rate of 8 to 12%. Adults can live 40 to 70 years or even longer. As adults the average survival rate increases to around 45%. In adults there is a 4:1 male to female ratio, which is probably a reflection of the prolonged amount of time females are exposed to terrestrial predators while laying eggs.

Behavior

Western pond turtles are not generally territorial although aggressive encounters including ramming, biting, and threatening with open-mouth gestures are common over basking areas. They tend to hunt late in the day and bask intermittently in order to maintain an average body temperature of 28 degrees Celsius. The maximum body temperature is 40 degrees Celsius, although they usually avoid going over 34 degrees Celsius. This species is most active in water that reaches 15 degrees Celsius. Although primarily associated with an aquatic environment, these turtles also spend significant amounts of time in terrestrial habits, primarily during overwintering and moving between aquatic areas. They move between overwintering sites as well, usually 4 times.

• Key Behaviors
• terricolous
• natatorial natatorial
• diurnal diurnal
• motile motile
• sedentary sedentary
• hibernation hibernation
• solitary solitary

Home Range

Male western pond turtle home ranges average 1 hectare, or around 200 to 5623 square meters. Female home ranges average only 0.3 hectares or up to 2100 square meters. Juveniles have home ranges up to 3175 square meters or around 0.4 hectares.

Communication and Perception

Western pond turtles find food using both sight and smell. Moreover, based on the mating ritual it is clear that touch is important in communication among sexes.

• Communication Channels
• tactile tactile

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

Western pond turtles are omnivores. Animal prey includes crustaceans , midges , fish , dragonflies , beetles , stoneflies , grasshoppers , and caddisflies . They will eat carrion as well. The plant portion of their diet consists primarily of willow ( Salix ) and alder catkins ( Alnus ), tule grass ( Scripus ), ditch grasses ( Ruppiaceae ), pond lily inflorescences, and green filamentous algae. They have been observed using a "gape-and-suck" form of taking in small invertebrates in the water column. Males tend to eat more insects and vertebrates and females eat more algae and other plant material.

• Primary Diet
• omnivore omnivore

• Animal Foods
• amphibians
• fish
• carrion carrion
• insects
• aquatic crustaceans
• other marine invertebrates

• Plant Foods
• flowers
• algae

Predation

Their primary anti-predator adaptation is their thick carapace and wariness. At hatching, young turtles are both small enough and soft enough to make easy prey, so achieving adult size best protects these turtles from predation.

Ecosystem Roles

Western pond turtles are prey for numerous species and predators of other, smaller species. These turtles act as hosts for several parasitic organisms.

Economic Importance for Humans: Positive

There is no current documented economic benefit of western pond turtles. From the 1800s to the 1930s these turtles were sold for human consumption and collected for pet trade. This kind of trade is largely illegal today, although poaching may still occur.

• Positive Impacts
• pet trade pet trade
• food food

Economic Importance for Humans: Negative

There are no adverse effects of western pond turtles on humans.

Conservation Status

Current threats to western pond turtles are numerous and include fire, flooding, drought, upper respiratory disease, habitat destruction, and lack of genetic variation. The lack of variation is due to the isolation of individual populations over ranges to large to be covered by migration. Habitat destruction is the result of intense urbanization. Additionally humans pose a great threat via off-road vehicles, chemical spills, and incidental catch by fishermen. Lack of research has prevented western pond turtles from being added to the federal endangered species list.

Although recommended for the federal endangered species list, western pond turtles are currently only recognized as state species of special concern by the California Department of Fish and Game (CDFG). Western pond turtles have been extirpated for nearly 20 years in British Columbia, are listed as endangered in Washington, and as sensitive with critical standing in Oregon.

Other Comments

Western pond turtles are currently recognized as Emys marmorata , previously they were recognized as Clemmys marmorata .

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Joshua Nachman (author), University of Maryland, Baltimore County, Kevin Omland (editor, instructor), University of Maryland, Baltimore County.

References

Bettelheim, M. 2006. "Western Pond Turtle Natural History" (On-line). Atlantis Magazine: Rediscovering Our Lost World. Accessed April 20, 2008 at http://www.atlantismagazine.com/bettelheim/pondturtle.html .

Gray, E. 1995. DNA Fingerprinting Reveals a Lack of Genetic Variation in Northern Populations of the Western Pond Turtle (Clemmys marmorata). Conservation Biology , Vol. 9, No. 5: 1244-1254. Accessed April 20, 2008 at http://www.jstor.org/stable/view/2387062?seq=2 .

Ingles, L. 1930. A New Species of Telorchis from the Intestine of Clemmys marmorata. The Journal of Parasitology , Vol. 17, No. 2: 101-103.

Reese, D., H. Welsh. 1998. Comparative Demography of Clemmys marmorata Populations in the Trinity River of California in the Context of Dam-induced Alterations. Journal Of Herpetology , Vol. 32, No. 4: 505-515. Accessed April 20, 2008 at http://www.fs.fed.us/psw/rsl/projects/wild/reese/reese1x.PDF .

Reese, D., H. Welsh. 1998. Habitat use by western pond turtles in the Trinity River, California. Journal of Wildlife Management , Vol. 62/3: 842-853. Accessed April 20, 2008 at http://www.treesearch.fs.fed.us/pubs/3654 .

Reese, D., H. Welsh. 1997. Use of terrestrial habitat by western pond turtles (Clemmys marmorata): implications for management. Proceedings: Conservation, Restoration, and Management of Turtles and Tortoises. An International Conference. New York Turtle and Tortoise Society.: 352-357. Accessed April 20, 2008 at http://www.treesearch.fs.fed.us/pubs/3652 .

Office of Environmental Health Hazard Assesment. Exposure Factors for Western Pond Turtle (Clemmys marmorata). California: The California Wildlife Biology, Exposure Factor, and Toxicity Database (Cal/Ecotox). 1999. Accessed April 22, 2008 at http://www.oehha.ca.gov/cal_ecotox/report/clemmef.pdf .

USDA Forest Service. WESTERN POND TURTLE (Clemmys marmorata). Natural History.. Redwood Sciences Laboratory: Pacific Southwest Research Station. 1997. Accessed April 20, 2008 at http://www.krisweb.com/biblio/gen_usfs_ashtonetal_1997_turtle.pdf .

East Contra Costa County HCP/NCCP. Western Pond Turtle (Clemmys Marmorata). California: 2005. Accessed April 20, 2008 at http://www.cocohcp.org/hcp_nccp_content/hcp_nccp/app_figs/App%20D%20components/APP_D-10a_Western_pond_turtle_1-18-05.pdf. .

Herpetology Northwest. 2004. "Western Pond Turtle (Clemmys Marmorata)" (On-line). Herpetology Northwest. Accessed April 20, 2008 at http://www.herpetologynorthwest.org/nwherps/turtles/western-pond-turtle.html .

U.S. Department Of The Interior. Western Pond Turtle: Clemmys marmorata. California: Bureau Of Land Management. 1999. Accessed April 22, 2008 at http://www.blm.gov/ca/pdfs/cdd_pdfs/clemmys1.PDF .