As a California herpetologist and western pond turtle expert, I often joke about how I have the easiest job: identifying the one turtle species native to California. In California—and along the greater Pacific Coast, for the most part—western pond turtles are the only native freshwater turtle species you’re supposed to encounter in the wild. But laypersons and professional scientists alike are regularly confounded when trying to distinguish them from any number of non-native pond sliders (Trachemys spp.) that find their way into urban waterways and beyond, via the pet trade.
At the start of the pandemic, I set myself the goal of helping identify every turtle observation reported in California, Oregon, and Washington on iNaturalist ^(https://www.blogquicker.com/goto/https://www.inaturalist.org/), the biodiversity database powered by public observations, as a way to hone my identification skills and contribute my expertise to the community. iNaturalist’s image recognition software can be spot-on, but it isn’t perfect, and this—paired with incorrect identifications contributed by the well-meaning public—can muddy the waters when it comes to properly identifying turtles in California.
This is all the more important today because western pond turtles are now candidates for the federal endangered species list, and the state and federal agencies have turned to iNaturalist as a key resource in establishing where western pond turtles are and are not.
A good year into the pandemic and my assignment, I crossed paths with Brian Acord, a biologist with the California Department of Fish and Wildlife’s California Natural Diversity Database (CNDDB). He had been set the same task of identifying and verifying California turtle observations in iNaturalist. Together, we realized that the public and professionals alike were regularly confounded by “melanistic” pond sliders—especially adult male Trachemys turtles. Their markings can darken as they age, masking their vibrant yellows and reds, and revealing speckles and marbling against a matte background that more closely resembles western pond turtles. (I’ve highlighted some examples of this on iNaturalist.org ^(https://www.blogquicker.com/goto/https://www.inaturalist.org/journal/matthew_bettelheim/90937-examples-of-melanistic-pond-sliders-that-look-a-lot-like-western-pond-turtles).)
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To address this misidentification issue, Acord and I, along with Rachel Freund and Annie Chang, developed a photo-illustrated guide applicable up and down the West Coast that identifies 11 important diagnostic traits, including two key traits (the shape and arrangement of two different “scutes,” the plates on a turtle’s top shell) that any layperson can hang their hat on if they can get a good look at the turtle in question from any one angle. Of course, nothing beats a clear, sharp, close-up photo. In lieu of a Bay Nature-quality cover photo, the guide should help provide enough clues for the public to make a simple, educated decision: native turtle, or not native turtle. Simple, sure, but incredibly important for agency staff and land managers working to conserve the species.
Diagnostic traits aside, we have a few additional words of wisdom:
- Don’t assume it is a slider because you are in an urban setting;
- Don’t assume it is a native turtle because you are in a natural area;
- Don’t assume it’s either species because the other has never been reported there before.
These can be context clues, but not the sole basis of an identification.
To learn more about distinguishing western pond turtles from non-native sliders, or about the “melanism” in pond sliders that obscures their beautiful markings, check out our photo-illustrated guide below. I also go into a bit more detail on the physiological details in this post on iNaturalist ^(https://www.blogquicker.com/goto/https://www.inaturalist.org/journal/matthew_bettelheim/90583-guide-to-distinguishing-western-pond-turtles-actinemys-spp-from-common-pond-sliders-trachemys-spp).
Your Bay Area Turtle Guide
Printable version here: Guide to distinguishing California freshwater turtles ^(https://www.blogquicker.com/goto/https://bioaccumulation.files.wordpress.com/2024/03/03102024_final-poster_v4.pdf)
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