Chesapeake Bay Species Article Series: Diamondback Terrapins

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Environment

Mitigating threats to the most beloved reptile in the Chesapeake Bay

An iconic symbol of Maryland’s heritage, diamondback terrapins boast a rich history and play an integral role in the Chesapeake Bay ecosystem. Known for the distinctive diamond-shaped patterns on their shells, terrapins are the only turtle species in North America that live exclusively in brackish water. They thrive in tidal marshes, rivers, and sandy beaches—making the Bay an ideal habitat. Although terrapins spend most of their time in the water, females lay their eggs in sandy areas above the high tide line.  

In addition to their close connection to the Bay, diamondback terrapins also serve as a symbol of Maryland’s cultural identity. Not only are they the official state reptile, but Testudo, a diamondback terrapin, is also the mascot of the University of Maryland, College Park. In fact, Maryland celebrates Diamondback Terrapin Day every year on May 13 to pay tribute to this iconic species and raise awareness about its importance to the Bay ecosystem. 

But despite their popularity, diamondback terrapins face serious threats. According to the International Union for Conservation of Nature (IUCN), the species is currently listed as vulnerable. So, it’s critical to continue to focus on conservation efforts and implement management strategies to protect them. 

“Many of the threats to diamondback terrapins are due to humans,” says Chris Rowe, Ph.D., an associate professor at the University of Maryland Center for Environmental Science (UMCES) Chesapeake Biological Laboratory, who conducts field work at Naval Air Station (NAS) Patuxent River. “Human actions have an impact on terrapins’ environment and their ability to survive. So, it’s important to think about threats from the terrapins’ perspective—not the humans’ perspective—and ask ourselves, ‘What can we do to help?’” 

Threats to Diamondback Terrapins 

According to the Maryland State Archives, diamondback terrapins were once abundant in the Chesapeake Bay and were a popular source of food for colonists. However, historical overfishing, especially during the 18th and 19th centuries, led to serious declines in the population. It wasn’t until 2007 that Maryland banned the commercial harvest of terrapins.  

The exact population of diamondback terrapins in the Bay is not known. Scientists say it’s difficult to estimate, and despite localized research, terrapin distribution and abundance are not well understood. But it is clear that the species faces numerous threats to its survival.  

Since terrapins are attracted to the same bait as blue crabs, they can become trapped and drown in crab pots. (Like all turtles, terrapins cannot breathe underwater.) To reduce bycatch among recreational crabbers, the Maryland Department of Natural Resources (DNR) implemented a regulation in 1999 that requires all waterfront property owners to equip each entrance funnel of their crab pots with Bycatch Reduction Devices (BRDs), also known as Turtle Excluder Devices (TEDs).  

An innovative idea, BRDs, which were developed by turtle conservationists, are rectangular inserts that prevent most terrapins from entering the crab pot, while still trapping blue crabs. According to the DNR, waterfront property owners are legally allowed to crab with a maximum of two recreational crab pots. Commercial crabbers aren’t required to use BRDs. 

Willem Roosenburg, Ph.D., professor emeritus, Ohio University, who grew up in Maryland and refers to it as his home state, says crab pots are an immediate threat to terrapins.   

“While BRDs are effective, there is no way to ensure compliance,” Roosenburg says. “So, we don’t know how many recreational crabbers are actually using them. BRDs can be an important tool to help terrapins survive and live a long life. But compliance remains a significant concern.” 

Habitat loss is also a major threat to diamondback terrapins. The brackish marshes and sandy beaches that they rely on for survival are being lost due to erosion. Although bulkheads and riprap are used to harden shorelines and prevent erosion, these man-made structures negatively impact the environment and can result in the loss of vital habitat for terrapins. Living shorelines offer a natural alternative to address erosion and are beneficial to the environment. 

The loss of sandy beaches is a significant concern since females use these areas for nesting habitat. Terrapins mate in the water in early spring. Females come onto the beach and dig a shallow nest in the sand during late spring and summer. They lay 10 to 15 eggs and may lay several clutches during the breeding season. The eggs hatch in 60 to 100 days. 

“Hardened shorelines present barriers to the movement of terrapins between the water and their nesting sites on land,” Rowe says. “Erecting a bulkhead or riprap shoreline destroys the natural land-water interface and physically isolates potential nesting sites where female terrapins cannot reach them. Living shorelines preserve the natural continuity between land and water that terrapins require.”  

In addition to the loss of much-needed sandy beach habitat for use as nesting sites, nest predation is also a threat to terrapins. Foxes, raccoons, snakes, and other animals eat terrapin eggs, resulting in a high offspring mortality rate. Rowe says placing protective cages, typically made of wire mesh, around the nests can protect the eggs from predators.  

“Nest and hatchling survivorship is very low among diamondback terrapins,” Roosenburg says. “To maintain the population, it’s critical to ensure that adults have high survival rates. If terrapins survive their younger years, they can live for long periods of time.”   

And, of course, climate change is an ongoing threat with potentially serious consequences, including increased habitat loss due to sea level rise and changes in sex ratios among hatchlings due to warming temperatures. Reproduction of diamondback terrapins, like most turtle species, depends on temperature, a process known as temperature-dependent sex determination (TSD). More specifically, the incubation temperature of the eggs determines the sex of the hatchlings. Lower temperatures result in male hatchlings, while higher temperatures produce females. 

“Climate change can have a major impact on terrapins—leading to difficulties with reproduction, a higher proportion of females, and potential population decline,” Rowe explains. “Cooler incubation temperatures, which can be achieved by shading terrapin nests, may produce a higher proportion of male hatchlings.”  

Additional threats to terrapins include road mortalities, especially among females crossing the road to seek nesting sites, and boat strikes, which can cause serious injury or death. Drivers and boaters should stay alert to protect terrapins from harm. 

Since diamondback terrapins face several threats to their survival, large-scale restoration projects, educational programs, and citizen science programs are critical. The following is a snapshot of a few conservation efforts that help protect terrapins and demonstrate Maryland’s commitment to its beloved state reptile. 

Living Shoreline Construction  

Launched in 2021, the Hog Point Living Shoreline Project will not only protect Navy test and training operations but also diamondback terrapin nesting habitat. The project, which involves the design and restoration of six key shoreline reaches, will protect 4,870 linear feet of coast adjacent to NAS Patuxent River.  

A partnership between the NAS Patuxent River Environmental Division, the Naval Air Warfare Center Aircraft Division (NAWCAD) Sustainability Office, the Middle Chesapeake Sentinel Landscape, Southern Maryland Resource Conservation and Development (RC&D), UMCES Chesapeake Biological Laboratory, and many others, construction of the $6.36 million project began in January 2025. 

According to the project partners, the shoreline in this area has been receding at an alarming rate of seven to 11 feet per year—with some stretches losing up to 90 feet. In less than a decade, more than 2.5 acres of land and vital marsh habitat have disappeared. Without intervention, more land could be lost in the next 10 to 20 years.  

“Rock breakwaters, marsh sills, sand fill, and native marsh grasses are being used not only as the best engineering option to buffer wave energy and halt erosion at the site but also to rebuild coastal habitats and restore ecological function,” says Jessica McGlinsey, a Ph.D. student who studies diamondback terrapins at UMCES Chesapeake Biological Laboratory. “For over a decade, researchers have documented terrapin nesting on this shoreline, and the [project] design was [prioritized] to ensure continued access to nesting habitat. With more than 80 percent of the Chesapeake Bay’s shoreline already altered by human activity, preserving what remains is vital.” 

The project was funded by the Readiness and Environmental Protection Integration (REPI) project, Navy Conservation support, and a grant from the National Fish and Wildlife Foundation (NFWF).  

Terrapin Education and Research Partnership 

Diamondback terrapins play a vital role in educational programs in Maryland classrooms and offer hands-on learning opportunities for students. The programs, which are part of the Terrapin Education and Research Partnership (TERP), allow students to care for the terrapins, observe their behavior, collect growth data, and research the species’ natural history and its connection to the Bay. Maryland Environmental Service (MES), on behalf of the Maryland Department of Transportation Maryland Port Administration, partners with local organizations and schools to place the hatchlings in classrooms. 

Each fall, hatchlings are gathered from Poplar Island and provided to Maryland schools, where they stay until late April or early May. In the spring, students take a field trip to Poplar Island to release the terrapins back into their natural habitat—bringing the experience full circle.  

Poplar Island is a unique 1,750-acre restoration project located off Tilghman Island. The island is an ideal terrapin nesting site due to its lack of land predators, its sandy shorelines, and its variety of habitats. A method known as mark and recapture monitors the terrapins after they are released. This process involves marking them with a tag, releasing them, and capturing them at a later date. If a terrapin from one of the classrooms is recaptured, it can be scanned and identified. Roosenburg says mark and recapture is the best tool to study terrapin population. TERP is part of an ongoing research study conducted by Roosenburg, who has engaged in field work in Maryland since 1987 and monitored terrapins on Poplar Island since 2002. His study seeks to determine whether head-starting gives terrapins a higher chance of surviving in the wild.  

“Raising terrapins in the classrooms gives them a ‘head start’ before they are released into the wild,” Roosenburg says. “This conservation strategy helps them avoid predation or other threats they may encounter during the early stages of life when they are most vulnerable. TERP can help us determine if head-starting is an effective way to conserve terrapins.” 

According to MES, Poplar Island terrapins are raised and released through various programs operating under the umbrella of TERP, including the National Aquarium’s Terrapins in the Classroom program, which provides terrapins to 30 schools, and Arlington Echo’s Terrapin Connection program, which serves Anne Arundel County Public Schools. In addition, MES facilitates TERP for some schools on the Eastern Shore. 

“As a scientist who loves the Chesapeake Bay, working on Poplar Island and with TERP has been one of the most rewarding experiences of my life,” Roosenburg says. “When I see students who participated in the program, they always tell me how cool it was and how much they enjoyed it. I’m proud of the work we’re doing, and I hope it has an impact not only on the students but also on future generations.” 

Diamondback Terrapin Surveys  

The need for coordinated terrapin surveys was first identified by concerned individuals from across the state with a common goal: to gain a better understanding of terrapins and protect the species. Surveys during the peak breeding season (late May through early June) to estimate terrapin presence and distribution throughout Maryland were initiated in 2012. Participants used a tally sheet to record observations, and the process evolved over time. 

“Our surveys were initially carried out by interns,” says Sandi Smith, outreach and marketing coordinator, Maryland Coastal Bays Program (MCBP). “Recognizing the broader value of the effort, the program soon transitioned the surveys into a citizen science initiative. This shift not only expanded data collection efforts but also created valuable opportunities to engage and educate the public about the importance of diamondback terrapins and the challenges they face.”  

Since the results of the surveys were often random and inconsistent, a new program is currently under development that will standardize terrapin surveying throughout the Mid-Atlantic.  

The Delaware Center for the Inland Bays is the lead on this major effort, which will hopefully launch in 2026. The nonprofit organization has been working with Mid-Atlantic terrapin groups to streamline the process. This year, only land-based surveys will be conducted. Since the sites are limited, Smith says MCBP will not promote surveys this year, but they are looking forward to a bigger and better program next year, which will be land- and water-based. 

In addition, MCBP launched a nest protection program last year, which offers opportunities for volunteers to build cages to provide to the community to protect terrapin nests.  

“Working with the Maryland Department of Natural Resources Wildlife & Heritage Service, we connected with a group in New Jersey that developed a program that offered protection cages to place around terrapin nests,” Smith explains. “We have mirrored that program, thanks to material donations and volunteers from Home Depot. And we have cages available for anyone who has seen a terrapin laying eggs and would like to protect the nest.” 

To learn more about MCBP’s terrapin programs, contact Smith at sandis@mdcoastalbays.org. 

Looking Forward 

Rowe says the future of the Chesapeake Bay’s diamondback terrapins will be challenging, given the current threats and the changes that are occurring to the climate. Thus, community engagement remains critical to help protect this beloved state reptile for future generations.  

“Ongoing issues, such as anthropogenic [environmental change caused by humans] habitat destruction and bycatch in crab pots will be exacerbated by rising sea levels and warmer temperatures,” Rowe suggests. “Despite this, it’s unlikely that the Bay’s terrapins will disappear in the near term. But they are [likely] to become less abundant in their distribution as they cling to what high-quality habitat remains. Terrapins are just one part of the Bay ecosystem. If people make choices that are considerate of the health of the Bay, terrapins will benefit as well.”  

Special thanks to Chris Rowe, Ph.D., the University of Maryland Center for Environmental Science (UMCES) Chesapeake Biological Laboratory; Willem Roosenburg, Ph.D., professor emeritus, Ohio University; and the Maryland Coastal Bays Program for providing the photographs for this article.