30 years of data show spotted turtle communities are still vulnerable

by Lisa Sheppard

A spotted turtle in water

Populations of the endangered spotted turtle in Illinois are holding up better than those in other states, based on 30 years of data at the University of Illinois. Still, only two populations remain, and the predictions are poor.

The small, semi-aquatic spotted turtle (Clemmys guttata) lives in sedge meadows, cattail marshes, and wet prairies, and in Illinois is found only in the northeast. Female turtles can live up to 110 years and reproduce all their adult lives.

Today, only two populations have survived. Researchers at the Natural History Survey (INHS) and the Forest Preserve District of Will County have collaboratively studied nearly 1,000 turtles in two communities since 1988.

In one population, population growth rates remained stable, but they declined slightly for the second, according to INHS ecologist Mike Dreslik. Despite threats from limited habitats, predators, poaching, and traffic, Illinois populations are not experiencing the steep declines occurring throughout the remainder of the turtle’s range in the United States.

Under the worst-case scenario, INHS scientists project both Illinois populations to decline in the future, with numbers bottoming out in 10 to 15 years for the more vulnerable community.

“The spotted turtle population doesn’t disappear from the landscape quickly, but when populations decline, they do take a long time to respond to conservation and recovery efforts,” Dreslik said. “You don’t want the populations to get below the threshold of no return. Our results show we have time to manage and recover the populations, but not too much time.”

The juvenile survival rate for the spotted turtle is fairly high compared to other turtle species, but management actions targeting adult survival will have the greatest impact on the population growth rate, Dreslik said. In Illinois, adult survival should be increased or at least maintained.

“If you lose one adult female, you not only lose 40 or so clutches she would have had in her lifetime, but you also lose the clutches her offspring would have produced,” Dreslik said. “The loss of just a few reproductive females could cause the population to decline.”

The positive outlook the results show is really a best-case scenario, according to Christina Feng, the primary author of the journal articles published in Diversity and in Herpetological Conservation and Biology.  

“With such high stakes for the species, we can’t assume persistence is guaranteed without intervention,” Feng said. “Conservation strategies need to be implemented immediately, if they have not been already, and they need to be ongoing.”

Some management actions involve predator control, such as controlling predator levels and increasing and restoring suitable habitat. The researchers also notch the turtles’ shells to monitor individuals over time, helping to discourage poaching.

It is highly unlikely the spotted turtle will ever fully recover in Illinois, given that only two populations remain and they are located close to each other. Local changes to the water supply or quality would affect both sites.

“Even if both existing populations were to double or triple in size, having more individuals doesn’t negate the fact only two populations have survived,” Feng said. “However, growing the populations will make the population at each site more secure against local extinction, which is a worthy goal on its own.”

Media contact: Mike Dreslik, 217-300-0970, dreslik@illinois.edu

This post originally appeared on the Prairie Research Institute Blog. Read the original post here.

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