Hart Welsh, Ph.D.
Research Wildlife Biologist (retired)
Guest Contributor
Northwestern Pond Turtle (Actinemys marmorata); Southwestern Pond Turtle (Actinemys pallida)
Pond turtles are ancient freshwater denizens of the Pacific slope of North America, ranging from northern Baja California to Puget Sound in Washington, below 4,000 feet elevation. They were once so abundant in the lakes, ponds, creeks, and rivers of this region that they could be purchased in the food markets of San Francisco for 3-6 dollars per dozen. Now however, they are in decline, rare, or absent throughout much of their range, the result of the rapacious nature of humankind to abuse natural ecosystems everywhere. The damming of streams and rivers and their diversions for human uses have altered aquatic habitats throughout the region to the detriment of their abilities to support native aquatic species (hello salmon and yellow-legged frogs).
Recent research has indicated genetic differences in pond turtle populations sufficient to identify two distinct species, with those from the San Francisco Bay Area south and west of the Coast Ranges members of Actinemys pallida, and those east of the Coast Ranges and northward members of Actinemys marmorata. The southern species is in more extreme decline from habitat losses and the impacts of drought, however both species are vulnerable and in need of protection, which is why the US Fish and Wildlife Service has recommended them for listing at Threatened under the Endangered Species Act.
These turtles are long-lived animals (individuals marked as adults for a Ph.D. study in Trinity County in the early 1970’s are still thriving) that reproduce slowly, and therefore the loss of reproductive capacity (i.e., female demise) can have devastating effects on population status over the long term. Females in their reproductive life stage are the most vulnerable given their need to leave aquatic habitats to access upland terrestrial areas to nest. This often requires them to cross roads where many are killed by car and truck traffic.
Secondarily, the nests themselves are highly vulnerable to predation, mostly by meso-carnivore species (skunks, racoons, foxes, otters, etc.) that have greatly increased in local ecosystems as humankind has eliminated the alpha-predators that once keep their numbers in check.
Lastly, are the new hatched turtles themselves, no bigger than an Oreo cookie when they hatch; they must dig out of their nests and make their way across dry land to the aquatic habitat where their parents’ dwell. A highly dangerous journey for such a delectable meal for any roving carnivore. Several local zoos have started turtle head-starting programs to compensate for this vulnerability.
Finally, a more subtle threat that has recently come to light from research on the Trinity River is the negative impacts of an altered thermal regime on these turtles. As poikilotherms (cold-blooded) reptiles these turtles require daily solar basking to achieve body temperatures sufficiently high to allow foraging underwater for their food base of invertebrates and plant materials. The cold water that results from the dam releases on the main stem Trinity requires the turtles to spend significantly more time basking than their counterparts on the warmer undammed South Fork Trinity, thus allowing them less time foraging. These differences over the long term have resulted in physiological differences sufficient to alter reproductive capacity of the females between the two river forks by reducing their size on the main fork and thereby reducing the number of eggs each can carry. While clearly a subtle negative effect, over the long-term it will adversely influence population viability.
If you see a pond turtle crossing a road, it is either a female seeking a nesting site (spring or early summer) or a turtle on its way to hibernate for the winter (late summer and fall). Please stop and help it on its way in the direction it is heading. The turtle and I both thank you.