An Agate Original
A conversation with herpetologist Carol Hall.
Anyone short of wonder need only consider a turtle. Here, we walk a mile in their shells with Minnesota DNR researcher Carol Hall, who shares insights from her many years studying the lives and populations of the state’s turtles.
Agate: First the basics. How many species of turtles are found in Minnesota?
Hall: There are at least nine native, naturally occurring species: Snapping Turtle, Painted Turtle, Blanding’s Turtle, Wood Turtle, Northern Map Turtle, Ouachita (Southern) Map Turtle, False Map Turtle, Smooth Softshell and Spiny Softshell. A 10th, the Eastern Musk Turtle (sometimes called the Stink Pot) is somewhat questionable, with only one documented report in the state, near Rochester. They are also known to occur in the Mississippi River and backwaters in Wisconsin. An 11th, the Pond Slider—in particular, the subspecies known as the Red-eared Slider—is outside of its range in Minnesota and doesn’t occur naturally here. They’re a common pet store turtle that people have unwisely released into the wild. Releasing captive turtles is never a good idea, and it is illegal to release nonnative species. They compete with native populations and can spread diseases.
Agate: Of these species, the Wood Turtle and Blanding’s are listed as Threatened in Minnesota, and the Smooth Softshell is listed as Special Concern. How are these species doing at the national level?
Hall: Both Wood and Blanding’s Turtles will be reviewed range-wide in 2023 for potential federal listing. In the meantime, we’ve been collecting records to improve what we know about their distribution here in Minnesota. The southeastern Minnesota population of Wood Turtles, in particular, is unfortunately in pretty dire straits. We’re not having success locating females at several former nesting sites, and are not finding them in habitat that looks ideal. This is likely due to a combination of factors including changes in habitat. If you compare old aerial photos with recent images, you can see that, in general, there are fewer forest openings where the turtles forage on strawberries, land snails, worms, and slugs, among other items. Also, many sites that previously provided open sandy areas suitable for nesting are now overgrown with reed canary grass, an invasive species. And the number of acres of ag-land has increased through the years.
Agate: So, how long have you studied turtles?
Hall: Wow, let’s see. Well, I did my thesis on Blanding’s Turtles in the late 80s, so I guess it’s been more than thirty years!
Agate: Are there certain things that stand out for you, that continue to interest or impress you about turtles?
Hall: Well, for one, just think about the age of these critters—I mean, if you’re talking about Wood Turtles, they can live to be over 50 years, and Blanding’s Turtles, over 70. A recaptured female in Michigan was known to be at least 83 years old. Their life strategy is to mature late, often not reproducing until they’re 14 or 15 years old, or even older. Once mature, they don’t necessarily nest every year; they may take a year off since nesting can be quite stressful on a female. But it is likely that they continue to reproduce into their 70s and 80s. Their nest site fidelity can be impressive, too, with some turtles returning on almost the same day, at the same nest site. They’re such a unique group of animals. And we’re continuing to learn about them. For example, there was a project in Camp Ripley where researchers took Blanding’s Turtle hatchlings that emerged from a nest, put transmitters on them, then released them in what, by everybody’s opinion, was suitable wetland habitat for hatchlings. Instead, several hatchlings left the wetland and moved to adjacent uplands, shrub swamps, or lowland forests. There are definitely more aspects of their life history that we need to understand if we want to preserve critical habitat for all life stages.
Agate: As kids, we marveled at the fact that turtles could carry their “house” with them. They’ve developed these amazing shells over some 260 million years of evolution, which offer some protection from predators and the elements. But in what ways are they vulnerable?
Hall: In terms of natural predators, mammals such as raccoons, skunks and fox can destroy nests, by digging up the eggs. A little known cause of nest failure is due to Scuttle Flies, which lay their eggs inside a turtle nest cavity and their larvae feed on the developing embryos. This would only be apparent to someone who was monitoring nesting success, otherwise this mortality would go unnoticed. Hatchlings that do emerge are taken by wading birds, crows, mammals, fish, even larger turtles. Winter kill can also be an issue, especially with Snapping and Painted Turtles, during the months when they are dormant underwater. If there isn’t snow to insulate the ice, the ice gets deep and they either freeze solid to the substrate or there is mortality due to lack of oxygen. Sun penetrates ice and causes plants to absorb oxygen, so there can be nothing left for the critters.
On the human-caused side, road mortality is a major factor, both accidental and intentional. We clearly need more education, or awareness of the value of turtles, or something to change that mentality. Curbs and railroad tracks can be obstacles that turtles can’t overcome. In agricultural areas near rivers and lakes, heavy equipment can take a toll on adults and hatchlings. And illegal collecting continues to be an issue. Observant local citizens have been important in helping to report this when they see it. There is also licensed commercial harvest of Western Painted Turtles, Snapping Turtles and Spiny Softshell Turtles.
Agate: Are the populations of these species at levels that can sustain commercial harvest?
Hall: There was a sunset law put in place years ago so there would be no new harvesters permitted, but the existing ones were grandfathered in. (See Agate Extra, following). For awhile, the harvest went down then spiked up. From my point of view, this harvest needs to be seen in the context of all the other things impacting the turtles: our turtle populations can’t tolerate being hit from so many different threats.
Agate: Is climate change one of those threats?
Hall: Yes. Flooding is an issue, and due to climate change it is increasing in frequency and intensity. Riverine species, such as Wood Turtles, that nest on sand bars and sand points are vulnerable to flooding. Eggs are often laid in June, and now we’re getting these tremendous flood events in July or August that cover nests with water for longer periods— and not only water but silt (sometimes several inches), which makes it more difficult for hatchlings to emerge.
Agate: Can the eggs handle being submerged?
Hall: To a degree. It depends on their stage of development: the farther along they are in their development, the longer they can tolerate being submerged. But the literature suggests about 24 to 48 hours. There are other potential implications of climate change for turtles. If temperatures are too high, nest sites on sparsely-vegetated south-facing slopes can overheat, causing desiccation (drying) of the eggs. Also, we know that temperature can influence the sex of turtles: that is, temperature determines whether a turtle is born male or female. Sea turtles are that way. Snapping, Painted, and Map Turtles are temperature dependent. In Snapping Turtles, for example, warmer temperatures during the egg development produce more females. So, that could have an increasing impact on a population’s sex ratio. And if climate change leads to drought and loss of wetlands, turtles will lose habitat and be concentrated into fewer areas.
Agate: Judging by the number of people who will stop to help a turtle across the road, there are many people who care about turtles. In addition to acting on climate change, are there any great turtle conservation projects that interested people could support, or things to keep in mind to help turtles in our local communities? Maybe it’s time for a turtle license plate to raise awareness and some funds for conservation?
Hall: License plates would be great! (and appropriate pay-back given the mortality caused by cars). People can watch for turtles on the road, especially during the nesting season from late May into July. The DNR, MN Zoo and MNDOT are working together to identify significant road crossings and ways to manage them, in some cases partnering with local watershed districts using signs to alert drivers and tunnels under the road to provide safe passage for the turtles. On private land, you can preserve wetlands, and try not to disturb known nest sites along roadsides, in yards, gardens and fields. You could build a simple basking platform if you’re on a lake or pond, lashing together some cedar logs, for example, and anchoring them with sufficient chain or cable to allow for changing water levels. That can be a nice way to see what species you have in your area. Also, recreational boaters can be mindful not to disturb the sandy beaches where turtles are nesting. Safely helping turtles cross roads is an easy way to literally give them a hand.
Agate: So, it’s July, mid-summer. Where are we now, in a turtle’s world? What are they up to, and what’s next?
Hall: It varies by species and by which part of the state you’re in, but most will have likely nested in June, traveling to nest sites and returning to a pond, wetland, or river. Map and Painted Turtles may lay multiple clutches during one nesting season, often laying a second nest with a few eggs in July. Eggs develop in the nest cavity during the heat of the summer and young will emerge from the nest between August and October. Young hatchlings have a little yolk sac that provides nourishment as the hatchlings seek out places of refuge. Painted Turtle hatchlings often overwinter right in the nest, emerging the following spring. Adults overwinter underwater in deep wetlands, lakes, and rivers, typically on or near the surface of the substrate. Technically, it’s not hibernation but brumation, because reptiles don’t rely on fatty tissue required for hibernation. But in any case, they spend the winter in a state of dormancy, although some may move short distances. In spring, turtles emerge from their winter refuges to bask on nearby logs and shorelines. Then they disperse, moving to warm waters to find mates and food.
Agate: Maybe we could try to give those hatchlings and the next generation a better chance of growing old.
Hall: We are looking at options to improve nesting success and recruitment of young into local populations. Given Minnesota’s vast number of lakes, rivers, and wetlands hopefully turtle populations will be around for many generations to come, but it is increasingly evident that they will need our help.
Carol Hall has been a Herpetologist with the Minnesota Biological Survey since 1991, conducting surveys on MN’s amphibians and reptiles throughout the state. Over the years she has participated in several collaborative efforts to improve our understanding of the habitat use and movements of our rare salamanders, turtles, snakes and lizards.
Commercial turtle harvest in Minnesota
When legislation passed in 2003 to discontinue issuance of new commercial licenses to turtle trappers in Minnesota, those with existing licenses were “grandfathered in” and allowed to continue operating. But despite the fact that the number of licenses in the state has since dropped by more than half (now down to 22), the number of turtles harvested in some years may not have dropped as expected. According to DNR Nongame Research Biologist Krista Larson, the fact that 29 other states have banned commercial harvest of wild turtles has put increased pressure on states that still allow harvest. “Minnesota’s existing law regulates the number of traps allowed on a body of water, but does not limit the number of turtles harvested,” notes Larson. How many is too many? She points to a recent Missouri study. In 2018, the state of Missouri instituted a ban after studies demonstrated that the commercial harvest, as practiced, exceeded sustainable levels. Researchers used the same methods as commercial harvesters to collect Snapping, Smooth Softshell, and Spiny Softshell Turtles, then calculated the abundance of turtles and proportion of turtles harvested to model the effects. “Removal of even a small number of adult females, in particular, can have a devastating impact on a population,” notes Larson.
While turtle populations may not be expanding, the market is. From 2002-2012, the U.S. reportedly exported 126 million turtles overseas, a figure that includes both wild-caught and farmed turtles.
Minnesotans will have the opportunity to revisit this issue. A bill to ban commercial turtle harvest was introduced and passed in the Minnesota House in the last legislative session, but did not make it into law. Proponents—including the bill’s co-author, Rep. Fue Lee—intend to take up the measure again. Stay tuned. In the meantime, how about those turtle license plates?
Contact Minnesota Sea Grant for information on periodic public “Habitatitude Surrender” events to re-home unwanted pet turtles.
Thank you to Vera Ming Wong and David Spohn for allowing Agate to use their artwork and photos.