Systematics: Originally described as Testudo odorata by Pierre Andre Latreille in 1801 based on specimens from "les eaux dormantes de la Caroline." The type locality was restricted to the vicinity of Charleston, South Carolina, by Schmidt (1953). Sternotherus was first used for this species by Gray (1825). In the Virginia literature. Hay (1902) followed Gray (1855) by using Aromochelys odoratus. This generic name was synonymized by Stejneger (1902), who also synonymized Sternotherus and considered the appropriate genus to be Kinosternon. Dunn (1918, 1920) followed Stejneger by using Kinosternon odoratum. No other Virginia author and few herpetologists followed this recommendation, but instead used the two variations of the spelling of the most commonly used generic name, Sternotherus (e.g., Richmond and Goin, 1938; Conant, 1945; Werler and McCallion, 1951; Mitchell, 1985b, 1985d, 1988) or Sternothaerus (e.g., Hardy, 1972; Jopson, 1972; Klimkiewicz, 1972). (See "Remarks" in the S. minor account for additional comments.) No subspecies of S. odoratus are currently recognized.

Description: A small freshwater turtle reaching a maximum carapace length (CL) of 137 mm (5.5 inches) (Conant and Collins, 1991). In Virginia, known maximum CL is 129 mm, maximum plastron length (PL) is 100 mm, and maximum body mass is 318 g.

Morphology: Carapace elongated, narrow, and rounded in cross section in adults; carapace arched with a keel in immature turtles; vertebral scutes do not overlap; marginals 11/11, a single narrow cervical, pleurals 4/4, and vertebrals 5; 10th and 11th marginals on both sides are twice the height of marginals 1-9 counting anterior to posterior; 1st vertebral triangular with a squared- off posterior edge; bridge comprised of only axillary and inguinal scutes; plastron 71-79% of CL; plastron with 11 scutes reduced in size, exposing skin between them; posterior plastral lobe width <50% carapace width; single hinge allows limited movement of anterior plastral lobe; single gular scute; pectoral scute squarish in shape; chin and ventral side of neck each with a pair of barbels, pair on neck reduced in size in some individuals.

Coloration and Pattern: Carapace brown to black, often with an irregular pattern of black streaks or spots; carapacial pattern most prominent in small turtles but maybe obscured in adults and immatures by algae; plastron with brown to yellowish scutes; skin between plastral scutes white to yellowish; skin usually gray to black with a variable pattern of yellowish spots and streaks on legs and lower neck; head and upper neck tan to black; 2 distinct yellow to white stripes on each side of head, 1 above and 1 below eye, that meet on snout (also see "Geographic Variation"); surfaces of lower and upper jaws black.

Sexual Dimorphism: Sexual size dimorphism is not evident in S. odoratus. Mature males averaged 89.7 ± 15.4 mm CL (52.2-127.9, n = 560), 62.1 ± 10.3 mm PL (36.9-93.4, n = 560), and 111.0 ± 50.7 g body mass (23-292, n = 482). Mature females averaged 87.3 ± 9.9 mm CL (66.1-129.3, n = 628), 66.0 ± 8.2 mm PL (47.3-99.9, n = 628), and 109.6 ± 38.9 g body mass (46-318, n = 541). Sexual dimorphism index was -0.02. The thick tail of males terminates with a small spine and the anal opening extends beyond the posterior edge of the carapace (precloacal distance was 5-29 mm, ave. = 17.7 ± 4.6, n = 195). Males also have 2 small patches of raised scales behind the knee. The anal opening of females does not extend beyond the edge of the carapace (precloacal distance was 0-13 mm, ave. = 5.4 ± 1.8, n = 166). The amount of skin exposed between the plastral scutes is greater in males than females.

Juveniles: Hatchling Eastern Musk Turtles are patterned as adults. The carapace is black to dark brown with 3 keels, and the plastron is yellow. The head is black with 2 bright yellow stripes on each side. At hatching, stinkpots from across Virginia were 20.3-25.0 mm CL (ave. = 22.6 ± 1.4, n = 52) and 15.1-18.5 mm PL (ave. = 16.9 ± 0.8), and weighed 1.6-3.2 g (ave. = 2.4 ± 0.4). Eleven hatchlings from a Hanover County lake averaged 20.0 ± 0.5 mm CL (18.5-22.0), 15.2 ± 0.4 mm PL (13.9-16.5), and 2.1 ± 0.1 g body mass (1.8-2.5) (Mitchell, 1985d).

Confusing Species: This species could potentially be confused with Sternotherus minor, Kinosternon baurii, and K. subrubrum. Sternotherus minor has overlapping vertebral scutes, yellowish carapace and plastron, a 1st vertebral scute whose apex points posteriorly, 1 pair of barbels on the chin, and yellow and black stripes on the neck. Kinosternon baurii and K. subrubrum have 2 plastral hinges, triangular pectoral scutes, and no exposed skin between the plastral scutes. The former has 2 light lines on the side of the head and snout and usually 3 light stripes on the carapace. The latter lacks the carapacial stripes and, usually, distinct lines on the head and snout.

Geographic Variation: Studies by Seidel et al. (1981) and Reynolds and Seidel (1983) revealed no consistent geographic variation in morphology and genetics among populations throughout the broad range of this species. There is considerable geographic variation in body and head size in Virginia. Populations inhabiting the upper Tennessee River drainage and the New River have consistently larger heads as adults and are larger, on average, than populations east of the Blue Ridge Mountains. Increased head size is a growth phenomenon presumably associated with the mollusk diet, as juveniles do not have large heads. Eastern Musk Turtles in the larger eastern rivers that feed on mollusks also have large heads, but they are not as large as those of S. odoratus in southwestern Virginia.

Eastern Musk Turtles inhabiting the southwestern Virginia rivers exhibit considerable variation in the head pattern. The lower stripe may be faint or absent altogether. The upper stripe is often broken posterior to the tympanum and may have a short lateral projection. These turtles are also light brown to tan in color. Populations in eastern and northern Virginia do not possess these characters.

Biology: This is a highly aquatic turtle that seldom wanders far from water. It has been found in ponds, lakes, swamps, ditches, streams, and rivers. It does not occur in brackish water, as stinkpots cannot tolerate salt water (Dunson, 1986). None have been found in estuarine habitats or brackish marshes in Virginia. Preferred habitat in the Coastal Plain is swamps, ponds, and ditches with an organic substrate and vegetation. These turtles are abundant in ponds with these features in the Piedmont and in the reaches of southwestern rivers that harbor vegetation. Eastern Musk Turtles prefer crevices (resting sites) that are dark and low enough to touch the carapace (J. Jackson, 1988). The organic substrate in which these turtles burrow may also satisfy the same needs. Basking occasionally occurs, but there are few records of this behavior for Virginia populations. Eastern Musk Turtles have been found active March through November in Virginia; most records (99.9% of 1,352) are March-October. Body temperatures of active stinkpots in water averaged 18.9 ± 4SC (14.6-23.6, n = 3), similar to the corresponding water temperatures. One turtle caught on a branch above water had a body temperature of 19SC (air temperature = 20. 3°C). These turtles overwinter in soft organic substrate, in muskrat burrows, and under debris in the water.

Sternotherus odoratus is omnivorous. Most prey are picked up from the substrate after probing with their snouts. The following have been recorded for Virginia turtles: unidentified seed pods and seeds, beetles, moths, dragonflies, crayfish, and freshwater snails and mollusks. Three species of snails have been identified from Virginia specimens: Leptoxis subglobossa, Oxytrema simplex, and Pleurocera unciale (R. L. Hoffman, pers. comm.). Ernst (1986b) recorded algae (Cladophora, Spirogyra), leeches, snails, crayfish, larval and adult insects, tadpoles, and dead fish in a Pennsylvania population. Numerous predators eat Eastern Musk Turtles. These include raccoons (Procyon lotor), skunks (Mephitis, Spilogale), large wading birds, foxes (Urocyon, Vulpes), large fish, American Bullfrog (Lithobates catesbeianus), Snapping Turtles (Chelydra serpentina), and Northern Watersnakes(Nerodia sipedon) (Ernst, 1986b). Clark (1982) reported a shell in a bald eagle (Haliaeetus leucocephalus) nest on Virginia's Eastern Shore. Knight and Loraine (1986) incubated three Eastern Musk Turtle eggs after they had been eaten and defecated by an Eastern Kingsnake (Lampropeltis getula) in South Carolina; they hatched 50 days later. One juvenile Eastern Musk Turtle was found in a 239-mm largemouth bass (Micropterus salmoides) taken from Lake Anna, Louisa County, on 17 March 1977. Humans often kill them by decapitation after they are caught on fishing lines, and many drown in fish traps left unchecked. Eggs are probably eaten by raccoons and skunks.

All mating occurs in water. Elsewhere in its range, the mating behavior of S. odoratus occurs in spring (Ernst, 1986b) and fall (Mendonca, 1987). Mendonca found that short day length was the environmental cue stimulating male sexual behavior in South Carolina and Tennessee. Ernst (1986b) observed mating between 0915 and 1027 hours in Pennsylvania. The highly aquatic habits of Eastern Musk Turtles make it difficult to see mating behavior in the field. Mahmoud (1967) described the mating behavior of kinosternid turtles, which is similar for all species. Reproductive behaviors can be grouped into three phases: tactile (male chases, nudges shell, bites head, and attempts to mount female), mounting and intromission (male mounts female, grasping edge of her carapace with all four feet; male clasps her tail with the scale patches on his rear leg, holding it to one side; male loops tail under female and inserts penis), and biting and rubbing (male bites and rubs female head and neck while in intromission; female bites head and feet of male; ejaculation is accompanied by spastic contractions and stiffening of male's body). This style of mating has been called forced insemination (Berry and Shine, 1980).

Reproductive cycles of males and females were studied for a Hanover County, Virginia, population (Mitchell, 1985b, 1985d). Males in this population matured at 52 mm CL (age 2-3) and females matured at 66 mm CL (age 4). Females produced one to two clutches per year (Mitchell, 1985d, 1988). Nests are often shallow depressions in leaf litter and rotting stumps; they can also be found under logs, shore debris, and vegetation mats, or in the walls of muskrat houses (Ernst and Barbour, 1972). Ernst (1986b) found flask-shaped nests dug to a depth of 10 cm by the hind feet of females in loamy soil at distances of 3-11 m from the water. Shelled eggs have been found in Virginia females 14 April to 17 July, but most of the records (64.8% of 71) were in June (Mitchell, 1985d, 1988). Clutch size in females from throughout Virginia was 1- 9 eggs (ave. = 3.6 ± 1.4, n = 30). I recorded a clutch size of 1-7 eggs (ave. = 3.2 ± 0.4, n = 42) from a Hanover County lake (Mitchell, 1985d), and an average clutch size of 2.7 in a Henrico County lake (Mitchell, 1988). C. H. Ernst (pers. comm.) found an average of 3.4 eggs (2-4) for Eastern Musk Turtles in Fairfax County. Throughout its range, clutch size and body size increase south to north (Tinkle, 1961; Mitchell 1985d). Clutch size and measurements of egg size are positively correlated with female body size (Mitchell, 1985d, 1988). Eggs from Virginia females averaged 25.9 ± 1.5 x 14.7 ± 0.9 mm (length 22.2-28.5, width 13.0-16.8, n = 109) in size and weighed 2.1-4.6 g (ave. = 3.3 ± 0.7). In the laboratory, eggs hatched in 67-80 days (ave. = 75.5 ± 3.4) from 13 August to 20 September. I found in a Henrico County population that hatching occurred in the fall under natural conditions and Eastern Musk Turtles did not appear to overwinter in the nest (Mitchell, 1988). Overwintering in the nest does occur in South Carolina (Gibbons and Nelson, 1978).

In a population ecology study of Eastern Musk Turtles in a Henrico County, Virginia, location, population size was estimated to be 534 ± 45 individuals in a golf course lake (188 per hectare) (Mitchell, 1988). Survivorship was estimated at 83.4-85.8% for all age classes. Overall sex ratio was 1:1 and the population was estimated to be growing by 3.2% per year. Most Eastern Musk Turtles remained in the lake during the study period and little immigration or emigration occurred. Dodd (1989) found a population density of 149 turtles per hectare in an Alabama lake and a sex ratio skewed toward females. Ernst (1986b) found a density of 24 per hectare in a Pennsylvania marsh and mill pond and a sex ratio skewed toward males. Obviously, there is considerable variation in the population characteristics of this turtle. Gibbons (1987) recorded Eastern Musk Turtles living as along as 15-19 years under natural conditions in South Carolina.

Sternotherus odoratus is highly aquatic and these turtles may be characterized as bottom walkers (Berry and Shine, 1980). Most of their time is spent bumping along the bottom searching for prey or mates. Basking does occur on occasion but is usually on an overhanging limb. Eastern Musk Turtles of all sizes may attempt to bite when caught. The curved beak can inflict a moderate wound.

Remarks: Other common names applied to S. odoratus are stink pot and marsh turtle (Hay, 1902), stinking jim (Dunn, 1918), and moon turtle.

The musk of Eastern Musk Turtles is derived from four glands located under the carapace anterior and posterior to the bridge. Stinkpots discharge about a drop of the fluid from each gland when disturbed, although not all individuals do so. The odor has been described as musky; it is vile enough to earn this turtle its common name. The fluid is a form of phenylalkanoic acid (Eisner et al., 1977).

Conservation and Management: Eastern Musk Turtle are commonly found in a wide variety of habitats and are quite abundant in some locations. Its status in Virginia is apparently secure. Sternotherus odoratus may, however, be a good indicator of habitat quality since it is highly aquatic. Population changes, changes in reproductive characteristics, and signs of disease based on changes in body mass and shell erosion could be used to monitor the effects of pollution in and perturbations of freshwater habitats. Management of aquatic systems to ensure the presence of viable populations of Eastern Musk Turtles requires the maintenance of emergent and submergent vegetation and shallow areas with organic substrates, along with hardwood forests along the shore for egg-laying sites.