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A USGS study examined adult southwestern pond turtles, a CA Species of Special Concern, at study sites along the Mojave River in California during turtle activity season from 1998-1999 and 2016-2019 for injuries and abnormalities from predation, human activities, and natural environmental influences.

A southwestern pond turtle (Actinemys pallida) in riparian vegetation in the sun next to water, Mojave River, CA
A male southwestern pond turtle (Actinemys pallida), Mojave River, CA. This turtle is missing its left foot. Photo by Shellie Puffer, 2017, SBSC, USGS.

The southwestern pond turtle (Actinemys pallida) is a rare, semiaquatic turtle that occasionally spends time on land to bask, lay eggs, make intermittent overland movements, and overwinter on land. It was until recently considered a subspecies of the western pond turtle (Actinemys marmorata), which is a Species of Special Concern in California, and has now been recognized as a distinct full species.

Little is known about the ecology of Actinemys pallida. Its range, as currently known, extends from the southern portion of California into northern Baja Mexico, and it inhabits ponds, rivers, streams, and other natural or artificial pools where water is present throughout most of the year.

Semiaquatic turtles’ use of both aquatic and terrestrial environments exposes them to an increased risk of injury or mortality and threats from a variety of factors. Environmental factors include flooding, drought, and predation. Human activities that pose hazards are unethical target shooting of turtles, the introduction of invasive species, livestock grazing, land development, roadway infrastructure, vehicle strikes, and dams in rivers that cause unnatural flows and barriers to turtle movements.

Although California has lost over 90% of its wetlands and experienced significant water losses from groundwater pumping, the Mojave River still flows intermittently at places along its course. Small, relict populations of Actinemys pallida still exist in perennial pools along some of these stretches.

USGS researchers conducted studies of physical abnormalities and injuries to adult Actinemys pallida at study sites along the upper and lower lengths of the Mojave River in San Bernardino County, California. The studies were timed during periods when turtles were most active, between May and October 1998–1999, and again from April to September 2016–2019.

Southwestern pond turtle (Actinemys pallida) partially emerged from the water, Mojave River
A female southwestern pond turtle (Actinemys pallida) basks in the sun, Mojave River, CA. Photo by Shellie Puffer, 2017, SBSC, USGS.

During these time periods and at all sites combined, they found 84 pond turtles.

Here’s what they observed:

Shell injuries at the study sites were common, with nearly 75% of turtles across all sites exhibiting injuries and 5% with both body and shell injuries.

  • In the upper half of the Mojave River sites, 78% of the turtles had injuries (damage inflicted by force to the shell or body), and 17% showed abnormalities (natural variations in the shells or bone morphology).
  • In the lower half of the Mojave River study sites, 68% of the turtles had injuries.
  • 4 turtles were found dead, at all sites combined.

The researchers found no statistical difference in the proportion of injured and non-injured turtles between the sexes, nor was the carapace (shell) length significantly different between injured and non-injured turtles at any of the sites. Injuries occurred in the majority of turtles at all sites and may be an indicator of the extent of threats facing these turtles.

Human influences present new and different challenges to semiaquatic animals like pond turtles. While the researchers suspect that attempted predation was the cause of most turtle injuries in the study, natural and human environmental influences must also be considered. Although previous studies suggest that females and larger turtles are more vulnerable to injury from predation and human threats, this study suggests that injuries to adult Actinemys pallida at these study sites are common regardless of sex or size.

This research was supported by the US Bureau of Land Management, California Department of Fish and Wildlife, The Living Desert, and the Mojave Desert Resource Conservation District.

Read the paper: 

Cummings, K.L., Lovich, J.E., Puffer, S.R., Greely, S., Otahal, C.D., and Gannon, J., 2022, Injuries and abnormalities of the southwestern pond turtle (Actinemys pallida) in the Mojave River of California: Western North American Naturalist, v. 82, no. 4, article 7, p. 719-733,

Associated data: Cummings, K.L., Puffer, S.R., and Lovich, J.E., 2023, Injury and abnormality data for southwestern pond turtles (Actinemys pallida) from 3 sites along the Mojave River, California from separate surveys in 1998-1999 and 2017-2019: U.S. Geological Survey data release,

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