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The Turtle and the Town: Freshwater Species of the Week

  The northern map turtle (Graptemys geographica) is a relatively large aquatic turtle that is native to North America. It is named for the lines on its shell, which resemble the contour lines on a map. Map turtles show extreme sexual size dimorphism, which means the genders grow to different sizes. Northern male map turtles...


Northern map turtles are endangered in Maryland, but thriving in Port Deposit. Photo courtesy of Towson University

The northern map turtle (Graptemys geographica) is a relatively large aquatic turtle that is native to North America. It is named for the lines on its shell, which resemble the contour lines on a map.

Map turtles show extreme sexual size dimorphism, which means the genders grow to different sizes. Northern male map turtles reach a carapace (shell) length of 3.9–6.3 inches (10–16 centimeters) and weigh between 5.3–14 ounces (150–400 grams). Females are much larger, with a shell length of 7.1–11 inches (18–27 centimeters) and weight around 1.1–5.5 pounds (0.5–2.5 kilograms).freshwater species of the week

The northern map turtle inhabits a swath of the eastern U.S. and southern Canada, from south Ontario and Quebec to northern Georgia, and as far west as eastern Kansas. Along the East Coast, the turtle is found only in the Susquehanna River in Pennsylvania and Maryland and the Delaware River.

Northern map turtles prefer relatively large bodies of water with rocks and fallen trees for basking sites. They dine on mollusks, their favorite food, but will also take insects and crayfish. They prefer to lay their eggs in sandy soil near the shoreline.

Northern map turtles are considered endangered in Maryland, Kansas, and Kentucky, although the species’ overall status is not officially listed. The turtles have been impacted by development, pollution, and hunting. Collection is prohibited in nine states.

Richard Seigel, a professor of biology at Towson University in Maryland, has been studying northern map turtles in the Susquehanna River. His team has been working in the small town of Port Deposit, Maryland, a hamlet of some 653 people that is on the north bank of the river near its mouth in Chesapeake Bay.

Water Currents asked Seigel a few questions about the conservation efforts there and this shy turtle, which tends to hide at the slightest suggestion of a threat.

Tell us about the turtle and the town.

Typically when you have an endangered species that has habitat requirements within any town boundaries there is potential for conflict and fears that there will be rules and regulations that will hamper the economy. But in the case of Port Deposit, the opposite happened.

The town adopted the turtle as its symbol and mascot, and the town has put its money where its mouth is. It has gotten investment from the state and federal government and private funding, and it is making the turtle a center of economic development, through ecotourism.

Female map turtles are much larger than males. Photo courtesy of Towson University
Female map turtles are much larger than males. Photo courtesy of Towson University

How that happened is a much longer story, but the bottom line is that rather than the town responding with, “We don’t want anything to do with an endangered species,” they have been tremendously supportive of our research. They have been our eyes and ears for watching what the turtle does and they have taken all sorts of voluntary measures. It has resulted in a large series of grants and contracts to improve the habitat within the town.

They have a safe harbor agreement with the state of Maryland, which states that if by helping the turtle it starts to nest elsewhere that won’t restrict future development. The project has nine different agencies and organizations working together, very harmoniously, so it is one of those rare things in conservation biology where it seems to be working, without any legal actions or any of the things I’m more used to. We like to brag about it because it’s worked.

Gas House in Port Deposit, Maryland
The Gas House. Photo courtesy Towson University

What’s the status of the habitat restoration work and the planned ecotourism and education center (in a restored 19th century building)?

That is all going to be done after this nesting season (May 15 to July 15).

There are three main components: In part A the shoreline where the turtles emerge from the river is being rehabbed by the Maryland Department of Natural Resources, to restore what they call a “living shoreline,” since that habitat had been degraded. Part B is removing brick and soil from where the turtles currently nest and putting down replacement soil. They will surround that with a privacy fence and put up barriers so they don’t go wandering into the marina and town.

Stage C is the gutting and rebuilding of the historic Gas House as a combo environmental education center and field station for our research. A and B will be done this summer and fall but stage C is going to take longer. That’s the most expensive.

How has it brought the town together?

One of my grad students, Teal Richards-Dimitrie, understood the need to get local town folks involved, so she came up with a kind of citizen science idea. She gave tours and talks and walked around, introducing herself and showing pictures of the turtles on tablets. Then people who would see a turtle would call her.

We found that almost all the nests the turtles built outside the town were destroyed by predators. The only place where nests were surviving was in Port Deposit, where we saw 100% nest success. We showed that the town nest sites were an important part of the story, and they realized the town needs more economic engines.

It’s a unique place, very beautiful, and the river is a magnet for boaters. It’s a fairly large turtle, so they thought maybe it is something that would get people to stop in the town. It makes Port Deposit unique. It took about a two-year period to get funding, and the state agreed they wouldn’t restrict future development. Very few people, if any, have voiced any opposition.

Port Deposit, Maryland waterfront
Port Deposit, Maryland. Photo courtesy of Towson University


Port Deposit put up a turtle crossing sign
Port Deposit put up a turtle crossing sign. Photo courtesy of Towson University

You have pointed out that northern map turtles eat zebra mussels. Do you think they could help control this invasive species?

The diet of the map turtles that live in Lake Erie has shifted to eating mainly zebra mussels; they are one of the few native species that eat them. Their jaws are designed to crush shells, so they have a field day with zebra mussels, since they are relatively small and easier to crush than native mussels. It’s sort of like having boneless chicken wings instead of having to debone them.

A few zebra mussels have been found upstream in the Susquehanna River and there has always been a big fear that they could come into the Chesapeake.

Zebra mussels are so abundant when established that I’m not sure if the turtles could control them. But in the beginning, when these turtles are out there foraging and eating large quantities of mussels, could they help prevent them from getting started? I think it’s a real possibility. It’s another lesson in why you don’t want to hurt native species.

What is the most surprising thing about the northern map turtle?

I think the fact that they have existed in this river so long without a lot of people knowing about them. We do most of our observation work from spotting scopes, and people come up and ask what we are doing. We tell them we are looking at turtles, and they say they fished there for a long time and didn’t know turtles were there. But now they start seeing them.

You have been working with a power company to time water releases in the river to help the turtles. How has that been going?

Our river system changes on an hourly basis depending on how much water is released for hydropower by Exelon Corporation. Susquehanna is an Indian name for river of rocks, and the channel has thousands of giant boulders in it. When the water is low you see them, but when it is high most of them are covered up, and the turtles don’t have many basking sites.

Northern map turtles need basking sites
Northern map turtles need basking sites. Photo courtesy of Towson University


Researchers examine a northern map turtle. Photo courtesy of Towson University
Researchers examine a northern map turtle. Photo courtesy of Towson University

We’re developing floating basking platforms that we hope will mitigate flow changes on turtle behavior. When water levels are high this will always be available, if the turtles will use it.

Exelon has been tremendously supportive of our work. One of the prime nesting areas outside of town had been choked with small trees and brush, so they hired landscapers to come in and open it up to make it more attractive to turtles.

Yes you can have endangered species, science going on, and economic development, it can all be worked out to everyone’s mutual benefit, including to the species under study.

Seigel is assisted by grad students Teal Richards-Dimitrie, Kaite Anderson, and Nathan Byer.

Brian Clark Howard covers the environment for National Geographic. He previously served as an editor for and E/The Environmental Magazine, and has written for Popular Science,,,, Yahoo!, MSN, and elsewhere. He is the co-author of six books, including Geothermal HVACGreen LightingBuild Your Own Small Wind Power System, and Rock Your Ugly Christmas Sweater.

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