(Baird and Girard, 1852)
Pacific pond turtle
This is a small to medium-sized (to 19 cm) turtle with a low carapace and, usually, a pattern of spots or lines that radiate from the centers of the scutes. The short, broad carapace is smooth, keelless, widest behind the bridge, and unserrated posteriorly. Vertebrals are broader than long; the 1st touches four marginals and the cervical. The carapace is olive, dark brown, or black, and the pattern may be absent in some individuals. Undersides of the marginals and bridge are marked with irregular dark blotches or lines along the seams. The pale-yellow plastron sometimes carries a pattern of dark blotches along the posterior margins of the scutes. Its hindlobe is notched posteriorly, and the plastral formula is: an > abd >< pect > gul > fem > hum. The head is moderate with a nonprojecting snout and a medially notched upper jaw, it may be plain gray to olive or have numerous black speckles or reticulations, and the jaws and chin are pale yellow. Other skin is gray, with some pale yellow on the neck, forelimbs, and tail.
The karyotype is 2n = 50: 16 macrochromosomes with median or submedian centromeres, 10 macrochromosomes with terminal to subterminal centromeres, and 24 microchromosomes (Bickham, 1975).
In males the plastron is concave; in females it is flat. In males the vent is posterior to the carapace margin; in females it is anterior to the margin.
The Pacific pond turtle ranges chiefly west of the Cascade-Sierra crest from western Washington to northern Baja California. Isolated colonies existed in the Truckee and Carson rivers in Nevada, but these are apparently extirpated (Buskirk, 1991a). Another isolated, but extant population is found in the interior-draining Mojave River of California as far into the Mojave Desert as Afton Canyon. There is a questionable record from Jerome County, Idaho, and the species has been seen in Grant Canyon, Oregon. Individuals collected on Vancouver Island, British Columbia, Canada, are thought to have been escaped or released captives originally from the United States, and records from the lower Fraser River watershed on the mainland of British Columbia are questioned by Buskirk (1991a).
Two poorly defined subspecies are recognized. Clemmys marmorata marmorata (Baird and Girard, 1852), the northern Pacific pond turtle, ranges from British Columbia south to San Francisco Bay and also occurs in western Nevada. It has a pair of well-developed, triangular inguinal scutes on the bridge, and the neck and head are well-marked with dark dashes. The throat is pale in contrast with the sides of the head. The southern Pacific pond turtle C. m. pallida Seeliger, 1945 occurs from San Francisco Bay south into Baja California. It can be distinguished by its poorly developed inguinal scutes (absent in 60% of individuals) and by the uniform color of the throat and neck. The Baja population may prove to be an additional subspecies.
Buskirk (1991a) reviewed the characters used by Seelinger (1945) to separate the two subspecies, and questioned their validity because of the ambiguity of several.
Clemmys marmorata is primarily riparian, most often living in sloughs, streams (both permanent and intermittent), and large rivers, although some may live in impoundments, irrigation ditches, and other artificial waterbodies (Buskirk, 1991a; Holland, 1994). In streams, pools are preferred over shallow reaches, and habitats are either rocky or mud bottomed, but usually contain some aquatic vegetation and basking sites. It has been collected from brackish estuarine waters at sea level to over 1800 m elevation in mountain streams. The turtles may leave the water and seek shelter in rock crevices on land (Holland and Goodman, 1996).
In the south, mature females are at least 10.0 cm in carapace length and 6-7 years old; but most do not reproduce until 12 cm and at least 8-10 years (Holland, 1994). In the north, the smallest gravid females are 13 cm and 10-12 years old. Males probably follow similar maturation patterns. The germinal reproductive cycles of both sexes are unknown.
Copulation occurs from May to late August in the wild, and to early September in captivity (Buskirk, 1991a). Holland (1988) observed that occurred on the bottom at a depth of 2 m. At first both turtles moved very slowly along the bottom. The female had pulled in her head but partially extended her legs. The male swam to one side behind and slightly above with his head and limbs fully extended. He made several scratching motions to the anterior rim of her carapace with his forefoot, which caused her to stop, retract her legs, and elevate the posterior portion of her shell 2-3 cm off the bottom by extending her hindlimbs. He then swam in front of her, turned to face her, and again scratched the anterior rim of her carapace with his foreclaws. His extended head also touched her carapace, but he did not bite her. He then moved 15-20 cm to the front and slightly to the left, fully extended his head, partially extended his left front and hind legs, and made several short, horizontal, coordinated sweeping/fanning movements which lasted about 25 sec. He then repeated the scratching and limb-sweeping sequences while elevating his body and extending his head and all four limbs. At this point the male discovered Holland and broke off contact with the female.
Nesting extends from late April through August, depending on the latitude; the peak period is late May to early July (Buskirk, 1991a; Holland, 1994). Nests may be dug either in the morning or evening; full sunlight seems to be requirement. The nests are flask-shaped, 6.5-12.5 cm deep, and 6.5-7.0 cm wide in the egg chamber.
Clutch size is 2-11 eggs, and some southern females lay two clutches a year (Goodman, 1997). The hard white eggs are elliptical-oval and 30.0-42.6 x 18.5-24.0 mm. In nature, known incubation time ranges from 80-100+ days in California to 94-106 days in Washington (Holland, 1994). In the south most hatchlings emerge in the fall, but a few hatch and remain overwinter in the nest; in the northern part of the range all hatchlings overwinter in the nest (Holland, 1994).
Hatchlings are 25-29 mm in carapace length. Their rounded and keeled carapace is brown or olive, with yellow markings at the edge of the marginals. Carapacial scutes have numerous small tubercles, which give them a grainy appearance. The plastron is yellow and has a large, irregular, dark central blotch. Head, limbs, and tail are marked with pale yellow.
Clemmys marmorata is a generalist feeder. Most food is obtained by opportunistic foraging, but neustophagia (modified filter feeding) is also used for capturing small, plentiful foods at the surface (Holland, 1985; Bury, 1986). Known foods are: pods of Nuphar, snails, crustaceans (crayfish, Daphnia), isopods, various insects, spiders, fish, frogs (tadpoles and adults), birds, and small mammals (Holland, 1985, 1994; Buskirk, 1991a; Ernst et al., 1994). Captives do well on canned and fresh fish, liver, raw beef, canned dog food, trout chow, earthworms, and romaine lettuce.
C. marmorata often can be seen sunning itself on rocks, logs, mudbanks, or mats of vegetation. Shy and wary, it dives into the water at the least disturbance. According to Pope (1939), during the middle of the day those not basking rest on the bottom of pools, but in the early morning and evening they move upstream or downstream, from one pool to another.
IUCN Red List Status (1996)
Vulnerable (A1cd). Clemmys marmorata has declined greatly in numbers in some places due to development, pollution of its habitat, disease and the pet trade; in past years it was exploited for food. This species is especially imperiled in the northern portion of the range, as well as the more developed areas in its southern range.