Western pond turtle (Actinemys marmorata)

Also known as: Pacific pond turtle
Synonyms: Clemmys marmorata, Emys marmorata
GenusActinemys (1)
SizeLength: 14 – 22 cm (2)

Classified as Vulnerable (VU) on the IUCN Red list 2007 (1).

The Latin name ‘marmorata’ refers to the marbled pattern of both the soft parts and carapace of many western pond turtles (3). The low, broad, smooth carapace is usually light to dark brown or olive in colour, either with no pattern or with an attractive pattern of fine, dark radiating lines on the scutes (2) (3). The limbs and head are olive, yellow, orange or brown, often with darker flecks or spots (3). Males are usually identified from females by the position of the cloaca. In males, the cloaca is positioned beyond the edge of the plastron, whereas it does not reach the edge of the plastron in females. Males also have a yellow or whitish chin and throat (4), a flatter carapace, a more concave plastron (indented underside of shell), and a more pointed snout than females (5). The taxonomy of the western pond turtle is currently under debate; at present, the IUCN Red List recognises that the western pond turtle belongs in its own genus, Actinemys marmorata (1), however, there is deliberation that it may belong to the genus Emys (6). There were previously thought to be two subspecies of the western pond turtle: the southern western pond turtle (Actinemys marmorata pallida) and the northern western pond turtle (Actinemys marmorata marmorata) (5), but now there is evidence for four separate groups, which do not match the distribution of the earlier described subspecies (7).

The range of the western pond turtle extends from Baja California Norte, north through the Pacific States of the USA, and barely into British Columbia, Canada. The handful of specimens found in British Columbia, Canada could represent introductions rather than native populations (8).

The western pond turtle species occurs from sea level to around 1,500 metres in mountains (2) (3). It is found in ponds, lakes, streams, large rivers, slow-moving sloughs, and quiet waters. The turtles prefer aquatic habitats with exposed areas for basking, with aquatic vegetation, such as algae and other water plants, but they also live in clear waters, especially where there is cover such as boulders or fallen trees in the water (4). The western pond turtle also spends significant amounts of time in upland terrestrial habitats and has been found more than one kilometre from water (5).

Breeding occurs in late spring to mid-summer (4), with mating taking place under water (5). Most mature females nest every year, some laying two clutches per season (5). In early summer the eggs are deposited in the nest, which is generally dug in soil, close to a water source, but some females may dig their nests many metres away from the water’s edge (9). The female lays an average of four to seven eggs (range 1 to 13) per clutch, which hatch after approximately 13 to 17 weeks (4); however, hatchlings from northern California northward over-winter in the nest (10). Western pond turtles develop slowly in areas with short or cool summers, taking up to eight years to reach sexual maturity. They can grow relatively fast in warmer regions and in some nutrient-rich habitats, where they can reach maturity in half that time (4). Turtles are thought to live up to 40 years (5).

Adults face predation by a number of carnivores including racoons, otters, ospreys and coyotes. Hatchling turtles, being small with soft shells, are easily preyed upon by raptors, ravens, weasels, bullfrogs and large fish. The diet of the western pond turtle includes some plants, small fish, frogs, carrion and, most importantly, aquatic insects and larvae (4). Western pond turtles bask on mats of floating vegetation, floating logs or on mud banks just above the water’s surface. In warmer climes they engage in aquatic basking by moving into the warm thermal environment in or on top of submerged mats of vegetation (4).

The western pond turtle is rare from mid-Oregon north and from the Los Angeles basin south, but is relatively abundant in the centre of its range in southern Oregon and northern California (2). In specific parts of its range, the greatest current threat for the western pond turtle is loss of habitat and fragmenting populations, through conversion of wetlands to farmlands, water diversions and urbanisation (5). In the past the western pond turtle, like other turtles, was intensively collected for the pet trade, but this has declined dramatically in recent years (4). Occasional losses occur through the illegal collection of turtles for food by immigrant populations from Asia, mortality from motor vehicles and predation from introduced species such as the bullfrog (5).

Commercial harvest or take of western pond turtles has been prohibited in all U.S. states where it is found since the 1980s (5). It is listed as Endangered in Washington State, and protected in Oregon and California (4). The recent increase in stock ponds and other man-made water sources appears to have a positive impact on population numbers and a few “head-start” programmes claim to have had excellent survivorship rates after being released into the wild (3). “Head-start” programmes are where the young are raised in captivity until their shells begin to harden and they are less susceptible to predation. However, re-introduction is limited if the habitat of the species is not protected.

For further information on the western pond turtle see:

Authenticated (30/01/08) by Dr. R. Bruce Bury, Zoologist, U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center.

  1. IUCN Red List (July, 2014)