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Southern Pacific Pond Turtle

Actinemys marmorata pallida



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Southern Pacific Pond Turtle Project on the Kern River Preserve


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Biology of Southern Pacific Pond Turtles

Kern River Research Station Turtle Project

Male Southern Pacific Pond Turtle, notice the pale throat and thick tail.

A male hatching Southern Pacific Pond Turtle.

Female Southern Pacific Pond Turtle notice the thin tail and the spotted throat.

Photos courtesy Alison Sheehey ©

The Pacific pond turtle was once abundant in California, Oregon, and in the Puget Sound area of Washington but has been declining through most of its range since the mid-1800's. Prior to the arrival of people of European descent, it is estimated that 4 million turtles lived in and around Tulare Lake in the San Joaquin Valley. Local commercial collecting activities for the restaurant trade in the Tulare Lake and Buena Vista basins caused a major decline in the population. Commercial harvest from all western state lakes decimated the population long before dams squeezed of the water supply from millions of acres of habitat. A report from San Francisco in the 1890's showed an average of 18,000 sold for food annually.  Pond turtles reproduce very slowly and populations cannot recover from mortality to adults from harvesting. Continued exploitation and habitat destruction continue to dramatically reduce pond turtle populations.


In the order Testudines and the family Emydidae, the Pacific pond turtle (Actinemys marmorata) (although some turtle biologists are now using Emys m. and some continue to use the former genus name Clemmys m.) has been known variously as the western pond turtle, western mud turtle, Pacific mud turtle, Pacific terrapin, and Pacific freshwater turtle. Baird and Girard described the Pacific pond turtle in 1852 after collecting the type specimens during an 1841 U.S. Exploring Expedition in the vicinity of Puget Sound, Washington.

Two subspecies: the northern Pacific pond turtle (A. m. marmorata) and the Southern Pacific Pond Turtle (A. m. pallida) were described in 1945. The northwestern subspecies is distributed from Washington's Puget Sound south to the Sacramento Valley. The Southern Pacific Pond Turtle is found from near Monterey, California south to Baja California, Mexico. The two subspecies are thought to interbreed in the northern San Joaquin Valley. DNA studies may change the assumed relationships between the two subspecies, as the most northerly and southerly regions may show enough distinction to be renamed as completely different species.


The Pacific pond turtle is a medium-sized turtle. Maximum size varies geographically, with the largest animals (210 mm or 8.2 in) occurring in the northern part of the range.  Turtles become sexually mature at a carapace length of about 120 mm.

Color: Carapace (upper shell) dark brown or olive above without dark streaking - Plastron (lower shell) cream to yellowish, sometimes with dark blotches in the centers of the scutes

Size: length: adults 120mm-210mm, juveniles 32-120mm, hatchlings: 25-31mm

Weight: Males: average = 554 g (1.2 lb), Females: non-gravid average = 504 g (1.1 lb),        Hatchlings: 3-7 g (0.11-0.25 oz)


Behavioral Characteristics

Turtles bask in the sun when not disturbed. Basking has been noted in all months of the year in some areas, but generally increases in frequency through the spring and peaks in early to mid-June. Basking declines in summer until September, when another peak is observed. Turtles bask in warm water concealed in or under masses of floating vegetation or algae, or in shallow water relatively close to shore. Aquatic basking peaks in early to mid-July in most areas and declines by early September.

Pacific pond turtles are wary, with a well-developed sense of sight and a moderate sense of hearing. Escape behavior has been observed when the perceived threat is within 100 m (330 ft) or even further away. In the spring, early summer, and autumn most turtle activity is diurnal. They are mostly nocturnal in summer. During the summer the species may be most active in early morning and evening, and inactive during the heat of the day.


“Overwintering” refers to periods of reduced or no activity during the winter which may include periods of a hibernation-like state of reduced physiological activity. Western pond turtles overwinter from mid-October or November to March or April. Pond turtles may overwinter on land up to 500 m from the nearest watercourse. During a study in California, 10 of 12 pond turtles overwintered at upland sites. Preliminary observations from turtles in a pond environment suggest that juveniles overwinter in the water.


Pacific pond turtles locate food by sight or by smell, and spend considerable amounts of time foraging. Under normal conditions feeding behavior is solitary. Pacific pond turtles can only swallow food under the water. They normally forage along the bottom, searching carefully in submerged leaf litter and other detritus. They feed during the day all months except during the summer when they may feed at night as well.


The Pacific pond turtle is a dietary generalist. They prey heavily on aquatic invertebrates, such as the larvae of beetles, stoneflies, caddisflies, dragonflies and other insects. They will prey upon fish and frogs in stream environments. Scavenging has been noted on the carcasses of various mammals, birds, reptiles, amphibians and bony fishes. Where bullfrogs (Rana catesbeiana) occur with Pacific pond turtles, there is no evidence that turtles feed on either larval or post-metamorphic bullfrogs, although they may feed on their carcasses. Unpalatable elements in the skin of bullfrogs may deter predation by pond turtles. Use of plants appears to be limited except in the case of post-partum females, who may ingest large quantities of cattail or bullrush roots at certain seasons. Water lily pods and alder catkins are also eaten. In certain circumstances, turtles may eat large quantities of filamentous green algae.


Most Pacific pond turtles are somewhat sedentary, although they are capable of moving significant distances and occasionally travel several hundred meters in just a few days.


The Pacific pond turtle is found associated with a variety of aquatic habitats, both permanent and intermittent. They are found from sea level to approximately 1,375 m (4,500 ft) in elevation. The name western "pond" turtle is something of a misnomer, as it is more often associated with streams where ponds are scarce. Historically, Pacific pond turtles occurred in large numbers in the warm, shallow lakes and sloughs on the floor of the San Joaquin and Sacramento valleys. It is in the few remaining areas that approximate these habitat conditions that this species reaches its highest densities. Western pond turtles are usually rare or absent in reservoirs, canals, or other bodies of water heavily altered by humans. Pacific pond turtles may inhabit some large rivers, but are usually restricted to areas near the banks or in adjacent backwater habitats where the current is relatively slow and abundant emergent basking sites and sanctuary sites exist. They generally avoid heavily shaded areas.

Substrate and Vegetation

Habitats used by Pacific pond turtles may have a variety of substrates including solid rock, boulders, cobbles, gravel, sand, mud, decaying vegetation, and combinations of these. In many areas turtles are found in rocky streams with little or no emergent vegetation. In other areas they occur in slow-moving streams or backwaters with abundant emergent vegetation such as cattails or bulrush. Dense growths of woody vegetation along the edges of a watercourse, which may shade potential emergent basking sites, and make otherwise suitable habitats unsuitable for pond turtles.

Basking Sites

Pacific pond turtles spend a considerable amount of time engaged in emergent basking, and they are more abundant in habitat that have basking sites. Turtles use a variety of areas for emergent basking, such as rocks, sand, mud, downed logs, submerged branches, and emergent or submerged aquatic vegetation.

Water Conditions

Turtles have been observed with water temperatures as low as 1-2ºC (37ºF) and as high as 38ºC (100ºF). In general, turtles avoid prolonged exposure to water above 35ºC (95ºF).


Courtship and mating behavior have been observed from February to November. Age and size at development of secondary sexual characteristics varies geographically, but these are generally evident in both sexes by the time an animal reaches 110 mm (4.3 in) carapace length. The time required for males to achieve sexual maturity is not known, but is thought to be at least 10-12 years. Females as small as 111 mm (4.3 in), with an approximate age of 6-7 years, have been observed carrying eggs in southern California.

When preparing to lay eggs, females typically leave the water in late afternoon or early evening and travel a considerable distance. Females moisten the soil around the nest by urinating prior to digging the nest chamber. Excavation of the flask-shaped nest may require several hours to complete and the female commonly remains on or near the nest site overnight.

Clutch size varies from 2 to 13 eggs with the larger females laying more eggs. Unusually cold wet weather can cause total nesting failure. In southern California, some hatchlings leave the nest in early fall while in the northern part of the species range hatchlings overwinter in the nest.


Under undisturbed conditions possibly only 10-15% of the animals that hatch in a given year survive until the end of the first year. Survival from the first to second and second to third year is similarly low, but increases slightly by the fourth and fifth years. The average life expectancy of adults is not known, but is at least 42 years. The estimated maximum life-span based upon an extrapolation from known adult growth rates is 50-70 years.


There are many predators of pond turtles. The introduced bullfrog preys on juvenile Pacific pond turtles and other small turtles. Bullfrogs are native to the eastern United States, but have become abundant and widely distributed in the west since their introduction to Idaho in the 1890's, and to Oregon in the 1920's. Bullfrogs may be an important predator on hatchlings because both frequent shallow water habitat. Predation by bullfrogs and other predators may be responsible for the lack of juveniles in many pond turtle populations.

Other known predators include: Largemouth bass (Micropterus salmoides), Black bear (Ursus americanus), coyote (Canis latrans), raccoon (Procyon lotor), striped skunk (Mephitis mephitis), Bald Eagle (Haliaeetus leucocephalus), Osprey (Pandion haliaetus), gray fox (Urocyon cinereoargenteus), and domestic dog (Canis familiaris).  Predation by humans may take the form of wanton shooting, capture by hook and line fishing or entanglement in nets, collection for the pet trade or collection for food.

Suspected predators include bobcat (Lynx rufus), Great Blue Heron (Ardea herodias), Black-crowned Night-heron (Nycticorax  nycticorax), Golden Eagle (Aquila chrysaetos), Red-shouldered Hawk (Buteo lineatus), Sierra garter snake (Thamnophis couchii), rainbow trout (Oncorhynchus mykiss), and channel catfish (Ictalurus punctatus).


A prolonged drought in California (1985-1990) apparently resulted in declines of up to 85 percent in some populations and the outright elimination of others. Drought may function as a direct mortality factor by eliminating the habitat or prey base required by turtles for survival. Without adequate body fat reserves normally produced by late-season feeding, turtles may be unable to survive the stress of overwintering.

Disease and parasites

Pacific pond turtles may develop a syndrome similar to upper respiratory disease, the causes remains a mystery but may be a virus or mycoplasma. Pacific pond turtles essentially have evolved in isolation from most other turtle species for most of their history. Therefore exotic species most likely introduce pathogenic agents to which Pacific pond turtles have never been exposed, and thus have had no chance to evolve any level of resistance. If this is the case, the introduction of exotic species, particularly from unhealthy captive situations, (e.g. red-eared slider) may have catastrophic consequences for Pacific pond turtle populations. A herpes-like virus has been reported to kill captive Pacific pond turtles in California.


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