FAMILY: Emydidae

DESCRIPTION: The western pond turtle is a medium-sized turtle, reaching between 7 and 9 inches. Adult turtles have a yellowish belly, with dark blotches and black spots or lines found on top of their heads. Adult males tend to have a flatter shell than females, as well as thicker tails and yellow or whitish chins and throats. Female turtles have higher, dome-shaped shells, smaller heads, flatter bellies, and darker chin and throat markings. It is difficult to determine gender in juvenile turtles, but characteristics usually start showing once they become sexually mature, when their shell length is about 4 inches. Despite genetic separation, the two pond turtle species appear to have similar life-history traits and suffer from similar threats.

HABITAT: The western pond turtle is found in permanent and intermittent waters of rivers, creeks, small lakes and ponds, marshes, irrigation ditches and reservoirs. Turtles bask on land or near water on logs, branches or boulders. Terrestrial habitat may be just as important as aquatic habitat for this turtle. In some populations, males may be found on land for some portion of ten months annually, while females can be found on land during all months of the year due to nesting and overwintering (a form of hibernation).

RANGE: Historically, the western pond turtle's range reached into British Columbia, Canada, extending as far south as Baja California. Today its range has contracted considerably; the animal is now found natively in southern Washington, Oregon and California and has been introduced to Nevada. The western pond turtle can be divided into two genetically distinct portions of its range in California. Northern western pond turtles are those found north of San Francisco, including populations found in the Central Valley and further north. Southern western pond turtles are those found south of San Francisco on the central coast, including populations as far south as the Mojave River and Mexico. There is a broad zone of intergradation (populations that show characteristics of both species) where they overlap in Central California, including Yosemite National Park.

MIGRATION: Studies show that western pond turtles can be found overwintering more than 1,500 feet from aquatic habitat, as well as migrating over half a mile. There is also evidence of site fidelity, where many turtles return to the same site as the previous year to overwinter.

BREEDING: Mating typically occurs in late April or early May but may occur year-round. Females emigrate from their aquatic habitat to an upland location to nest and deposit between one and 13 eggs. Females may lay more than one clutch a year, but they most commonly deposit eggs between May and August. The western pond turtle usually nests on sandy banks near water or in fields with sunny spots up to a few hundred feet from water.

LIFE CYCLE: Hatchlings stay in the nest after hatching until spring, following a similar pattern to the adults' overwintering. On average they enter the water after 48 days, taking up to a week to move from their nesting site to aquatic habitat. Overwintering and aestivation — in which the turtles enter states of dormancy during hot and cold periods to preserve energy — are both important activities. Western pond turtles are thought to be long-lived, since the minimum age of a recaptured individual was 42 years.

FEEDING: Turtles are dietary generalists and highly opportunistic; they will consume almost anything they are able to catch and overpower. Western pond turtles exclusively forage and feed in the water. Turtles cannot swallow air, so all their food must be swallowed in the water.

THREATS: Both species face similar threats, primarily due to habitat alteration and destruction. Dam construction along the West Coast upsets their natural life cycle, disturbing river flows and draining natural wetlands for urban and agricultural development. Diseases such as ulcerative shell disease and upper respiratory disease threaten to decrease populations of both species, especially through the introduction of invasive species such as the red-eared slider, bullfrog and largemouth bass, which create competition for resources and prey on the turtles. Invasive plants such as the reed canary grass can also prevent females from navigating to nesting sites. Human disturbance is also still a major threat — from disturbance of basking turtles to people actually shooting turtles for sport. In addition, these turtles have never fully recovered from a period during which humans overharvested them for the San Francisco restaurant industry during the early 20th century. And these turtles are particularly sensitive to harm from chemical contaminants left over from the mining and agricultural industries, since their broad diet and long life span are conducive to accumulating large amounts of contaminants over time.

POPULATION TREND: Although western pond turtles are found all along the West Coast, both species have suffered an overall reduction in their population sizes, with much of this loss irreversible. Historically their range reached into British Columbia, Canada, but today no Canadian populations exist. These turtles' most abundant population lives within the Trinity River watershed, where the majority of recent studies have taken place. Total population estimates are between 10,000 to 1 million individual turtles (of both species).

Western pond turtle photo by Yathin S. Krishnappa/Wikimedia Commons