Malaclemys Research Articles

Effects of terrestrial–aquatic connectivity on an estuarine turtle

AbstractAimEstuaries world‐wide have been modified or fragmented due to human stressors in their terrestrial and aquatic components. Estuary fragmentation often results in reductions in species richness, diversity and connectivity. Effects of human modification on estuaries have been well studied, but less is known about how land use alters connectivity of the terrestrial–aquatic ecotone. We studied the relationship between terrestrial–aquatic connectivity and the distribution of an estuarine turtle, diamondback terrapin (Malaclemys terrapin).LocationChesapeake Bay, Virginia, USA.MethodsWe conducted diamondback terrapin surveys at 165 sites from late spring to mid‐summer in 2012 and 2013. We evaluated associations between terrapin occurrence, land use, salt marsh, shoreline armouring and crabbing intensity in concentric–circular neighbourhoods ranging from 0.27 to 2 km to cover daily and annual terrapin movements. We used occupancy modelling and model averaging to identify key terrestrial and aquatic variables explaining heterogeneity in terrapin occupancy. We evaluated the final model with an independent data set and identified occurrence thresholds for key variables.ResultsDiamondback terrapin occupy areas with ≥ 10% of marsh within a 750‐m neighbourhood, ≤ 17% armoured shoreline within a 1‐km neighbourhood, ≤ 20% of agriculture within a 500‐m neighbourhood, ≤ 33% low‐density housing within a 270‐m neighbourhood and ≤ 9 active crab pots within a 270‐m neighbourhood. Our model performed well when evaluated with an independent data set.Main conclusionsWe are the first to identify thresholds and quantify negative associations between the distribution of diamondback terrapin and alterations to terrestrial–aquatic connectivity from land development, shoreline armouring, and fishing activity. Because diamondback terrapin responses are reflective of changes in coastal habitats, especially marshes, terrapin occurrence can be used to direct wetlands conservation and restoration efforts.

When Drivers and Terrapins Collide: Assessing Stakeholder Attitudes Toward Wildlife Management on the Jekyll Island Causeway

Roads are a pervasive fixture on most landscapes and frequently impact wildlife. Management of road effects on wildlife should consider the attitudes and areas of contention among various stakeholders using the road. To inform future management of road impacts on the diamondback terrapin (Malaclemys terrapin), a species of conservation concern, we surveyed stakeholder groups on Jekyll Island, Georgia, USA to measure overall attitudes and value orientations relating to terrapin management and to evaluate the acceptability and potential for conflict among user groups regarding specific management alternatives. A majority of respondents supported the protection of terrapins, although support varied by group membership and value orientation. Specific actions that did not impact speed limits or road aesthetics were most acceptable, but substantial conflict existed for most strategies. We intend to use these results to improve communication and buy-in of stakeholders as we develop management alternatives for the diamondback terrapin on Jekyll Island.

Size-Based Mortality of Adult Female Diamond-Backed Terrapins (Malaclemys terrapin) in Blue Crab Traps in a Gulf of Mexico Population

Mortality incidental to trapping for blue crabs is a primary threat to diamond-backed terrapin (Malaclemys terrapin) populations. Due to sexual size dimorphism in this species, crab-trap mortality is believed to be biased toward smaller adult males and juvenile females. However, a comparison of commercial trap funnel openings and adult female size from a Gulf Coast population suggested that crab-trap mortality is a larger threat than previously thought to adult female terrapins in this population and possibly others.

Temporal and Spatial Variation in Survivorship of Diamondback Terrapins (Malaclemys terrapin)

Abstract The diamondback terrapin (Malaclemys terrapin) is a species of conservation concern that has experienced noticeable declines throughout its range. Mark–recapture studies have been conducted on terrapins at Kiawah Island, South Carolina, since 1983, and during the early 1990s, this population began to decline. Our objectives were to evaluate current spatial and temporal variation in survivorship and compare current estimates of survivorship with those calculated from 1983 to 1999 in a previous study. We used an 11-year data set (2003 to 2013) in a capture–mark–recapture analysis to estimate the survivorship of terrapins in 5 creeks. Among creeks, annual survivorship estimates ranged from 61% to 82% with no difference between the sexes. Survivorship was lower than that documented for this population in the early 1990s. Recent anthropogenic habitat modification, such as the construction of docks, roads, and housing developments, as well as activities such as crab-trapping, likely play a role in low ...

Distribution and Abundance of Diamondback Terrapins (Malaclemys terrapin) in Southwestern Louisiana

Abstract The diamondback terrapin (Malaclemys terrapin) is a brackish-water turtle ranging from Texas to Massachusetts, as well as an isolated population on the island of Bermuda. Louisiana likely holds the most available habitat of any other state for the species (over 650,000 ha of brackish and salt marshes), yet little is known about terrapin distribution and abundance throughout coastal Louisiana. Knowledge is particularly scant in southwestern Louisiana, where only 12 specimen records exist, the most recent record being from 1972. We wanted to determine whether 1) terrapin populations persist in historical collection localities, 2) terrapin populations are present in additional coastal marsh localities, and 3) terrapin abundance differs among sites in southwestern Louisiana. We sampled for diamondback terrapins during 2011–2013 at 16 sites across southwestern Louisiana; all sites were near historical localities or other apparently suitable brackish or salt marsh habitats. We used unbaited fyke nets w...

Effects of Vegetation Structure and Artificial Nesting Habitats on Hatchling Sex Determination and Nest Survival of Diamondback Terrapins

Abstract It is often the case that multiple factors contribute to wildlife population declines such that management will require simultaneous, integrated interventions to stabilize and recover populations. Diamondback terrapins Malaclemys terrapin are a species of high conservation priority, and local populations can be threatened by multiple factors, including bycatch in commercial and recreational crab pots, vehicle strikes on coastal roads, nest depredation from subsidized and introduced predators, and terrestrial habitat alteration. Mitigation of just one of these factors will often be insufficient for recovering at-risk populations; thus, information to manage multiple threats is needed. We measured the effects of natural vegetation structure and constructed (artificial) nesting habitat on hatchling sex ratios and nest depredation for a declining terrapin population on Jekyll Island, Georgia. Nest temperatures were highest on constructed nesting mounds, intermediate in open grass areas, and coolest under the shrub-dominated hedgerows. Higher nest temperatures led to shorter incubation times for nests on mounds and open habitat, such that all surviving nests on nesting mounds and open areas produced female hatchlings. In contrast, surviving nests under hedge produced 85% male hatchlings. Raccoon Procyon lotor predation rates of simulated (chicken egg) nests were highest on nesting mounds (95.3%), followed by hedge (84.4%) and open habitats (45.2%). Our results demonstrate that vegetation management can positively affect both production of female hatchlings and nest survival. Artificial nest mounds were successful at producing female hatchlings, but we documented high predation of simulated (chicken egg) nests despite structures to exclude predators. Further modifications to nest boxes atop constructed nesting mounds are needed for these devices to effectively contribute to population management. We suggest the relatively low cost and maintenance associated with removing shrubs and trees can be a viable strategy to manage large areas of nesting habitat for the increased production of female turtles, and to reduce the impacts of subsidized predators.

Nesting Habitat Creation Enhances Recruitment in a Predator‐Free Environment: Malaclemys Nesting at the Paul S. Sarbanes Ecosystem Restoration Project

AbstractAquatic turtles worldwide are plagued with habitat loss due to development and shoreline alteration that destroys the terrestrial–aquatic linkage which they must cross to reproduce successfully. Furthermore, nesting habitat loss can concentrate nesting, increasing nest predator efficiency. We describe how the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island created nesting habitat for Malaclemys terrapin (Diamondback Terrapin), and document nesting success in response to construction progress and the absence of raccoons and foxes, the primary nest predators. We monitored terrapin nests throughout the nesting seasons from 2002 to 2011 to determine overall and within‐nest survivorship. Female terrapins began nesting on the restoration project within 1 year but planned construction during the study eliminated some nesting areas and opened previously inaccessible areas. Overall, nest survivorship was considerably higher than mainland nesting areas due to the absence of raccoons and foxes on the island and within‐nest survivorship was similar. Egg size, hatchling size, and the frequency of shell scute anomalies were similar to other terrapin populations, suggesting normal developmental conditions on the island. We documented annual variation in hatchling size that correlated negatively with mean air temperature during the incubation season. Our results indicate that restored or created isolated island habitat can be located rapidly by terrapins and can become an important source of recruitment in regions where nesting habitat is limited and predation is high. Poplar Island illustrates how habitat loss and restoration can affect turtle populations by revealing the changes in nesting patterns and success in newly created, predator‐free habitat.

Evidence of eelgrass (Zostera marina) seed dispersal by northern diamondback terrapin (Malaclemys terrapin terrapin) in lower Chesapeake Bay.

The initial discovery in May 2009 of eelgrass (Zostera marina) seeds in fecal samples of wild-caught northern diamondback terrapins (Malaclemys terrapin terrapin) was the first field evidence of eelgrass seed ingestion in this species. This finding suggested the potential of terrapins as seed dispersers in eelgrass beds, which we sampled for two additional years (2010 and 2011). Seeds were only found in feces of terrapins captured prior to June 8 in all three years, coinciding with eelgrass seed maturation and release. Numbers of seeds in terrapin feces varied annually and decreased greatly in 2011 after an eelgrass die off in late 2010. The condition of seeds in terrapin feces was viable-mature, germinated, damaged, or immature. Of terrapins captured during time of seed release, 97% were males and juvenile females, both of which had head widths <30 mm. The fraction of individuals with ingested seeds was 33% for males, 35% for small females, and only 6% for large (mature) females. Probability of seed ingestion decreased exponentially with increasing terrapin head width; only males and small females (head width <30 mm) were likely to be vectors of seed dispersal. The characteristic that diamondback terrapins have well-defined home ranges allowed us to estimate the number of terrapins potentially dispersing eelgrass seeds annually. In seagrass beds of the Goodwin Islands region (lower York River, Virginia), there were 559 to 799 terrapins, which could disperse between 1,341 and 1,677 eelgrass seeds annually. These would represent a small proportion of total seed production within a single seagrass bed. However, based on probable home range distances, terrapins can easily traverse eelgrass meadow boundaries, thereby dispersing seeds beyond the bed of origin. Given the relatively short dispersion distance of eelgrass seeds, the diamondback terrapin may be a major source of inter-bed seed dispersal and genetic diversity.

Factors affecting temperature variation and habitat use in free-ranging diamondback terrapins

Measuring the thermal conditions of aquatic reptiles with temperature dataloggers is a cost-effective way to study their behavior and habitat use. Temperature dataloggers are a particularly useful and informative approach to studying organisms such as the estuarine diamondback terrapin (Malaclemys terrapin) that inhabits a dynamic environment often inaccessible to researchers. We used carapace-mounted dataloggers to measure hourly carapace temperature (Tc) of free-ranging terrapins in South Carolina from October 2007 to 2008 to examine the effects of month, sex, creek site, and tide on Tc and to determine the effects of month, sex, and time of day on terrapin basking frequency. Simultaneous measurements of environmental temperatures (Te; shallow mud, deep mud, water) allowed us to make inferences about terrapin microhabitat use. Terrapin Tc differed significantly among months and creek and between sexes. Terrapin microhabitat use also varied monthly, with shallow mud temperature being the best predictor of Tc November–March and water temperature being the best predictor of Tc April–October. Terrapins basked most frequently in spring and fall and males basked more frequently than females. Our study contributes to a fuller understanding of terrapin thermal biology and provides support for using dataloggers to investigate behavior and habitat use of aquatic ectotherms inhabiting dynamic environments.

Status of Diamondback Terrapins (Malaclemys terrapin) in North Inlet–Winyah Bay, South Carolina

Diamondback terrapin (Malaclemys terrapin) population dynamics in North Inlet–Winyah Bay, South Carolina, a relatively undeveloped salt marsh estuary, were determined from 6 yrs of mark–recapture data. Total terrapin abundance in 4 adjacent creeks was estimated annually at 260–360 terrapins (144–200 terrapins/km) and the mean annual survival probability for terrapins was 0.78. This study in a protected terrapin habitat will provide data for population models and comparisons with threatened populations.

The Status of Louisiana's Diamondback Terrapin (Malaclemys terrapin) Populations in the Wake of the Deepwater Horizon Oil Spill: Insights from Population Genetic and Contaminant Analyses

Abstract We studied the population-genetic structure of the Diamondback Terrapin (Malaclemys terrapin pileata) in Louisiana and used data from previous studies to compare our results with rangewide patterns of genetic diversity. We analyzed blood plasma to examine the contaminant load in Louisiana terrapins in the wake of the 2010 Deepwater Horizon oil spill. Using 16 polymorphic microsatellite loci, we tested for genetic structure to infer site fidelity, connectivity, and gene flow among terrapins in Louisiana estuaries. We found no evidence for population structure within Louisiana, even among sites up to 120 km apart. Comparing our Louisiana samples to data from previous studies using four loci, we found relatively low genetic diversity in Louisiana and other Gulf Coast terrapins. Based on their genetic similarity, our results support previous recommendations that two Gulf Coast subspecies be grouped into one management unit. The low genetic diversity we observed in Gulf Coast populations may be attrib...

The Influence of Recreational Crabbing Regulations on Diamondback Terrapin By-Catch

Malaclemys terrapin terrapin (Northern Diamondback Terrapin) is susceptible to drowning in commercial-style pots used for the Callinectes sapidus (Blue Crab) fishery. Regulations to reduce by-catch mortality vary by state. We compared three different regulatory strategies with respect to crab catch and their relative effectiveness at reducing terrapin by-catch. To mimic their possible use by recreational crabbers, we grouped and fished together ten unbaited crab pots with no by-catch reduction devices (BRDs), ten with large BRDs, and ten with small BRDs in a tidal creek in southeastern Virginia. Over 24 sampling days, the total legal crab catch (crabs ≥ 12.7 cm) in pots with no BRDs (29.9 ± 10.0 SD crabs pot-1) and large BRDs (27.9 ± 6.2 crabs pot-1) was significantly greater than catch in pots with small BRDs (14.0 ± 5.8 crabs pot-1). Legal crabs varied in average size from 14.1 ± 1.2 cm, 14.0 ± 1.2 cm, and 13.7 ± 1.0 cm from pots with no BRDs, large BRDs, and small BRDs, respectively, but these differences were not significant. Of a by-catch of 71 terrapins, 69 were from pots with no BRDs, 2 from pots with large BRDs, and none from pots with small BRDs. The potential mortality of terrapins in pots without BRDs would have reduced the population in this tidal creek by 42% in just 24 days. Based on these results, regulations requiring the use of large BRDs come closest to the objective of reducing by-catch mortality of terrapins without a large effect on crab capture in Virginia. Both recreational crabbing and commercial crabbing with no BRDs on pots in terrapin habitat can contribute to declines in local terrapin populations.

CHARACTERISTICS OF MANGROVE DIAMONDBACK TERRAPINS (MALACLEMYS TERRAPIN RHIZOPHORARUM) INHABITING ALTERED AND NATURAL MANGROVE ISLANDS

The Mangrove Diamondback Terrapin, (Malaclemys terrapin rhizophorarum) is dependent on a very broad array of the services provided by the mangrove ecosystem. We sought to evaluate both the turtles and their habitat by an integrated assessment of physical, chemical, and physiological parameters. Extreme site fidelity of the turtles to mangrove habitat was evident along with a strong female biased sex ratio. We provide blood serum values and microbial cultures as baselines from these turtles in the wild. Salmonella sp., a potentially zoonotic pathogen, was isolated from one female. Ultimately, the health of these turtle populations may be reflective of the integrity of the mangrove system on which they depend.

Regional differentiation among populations of the Diamondback terrapin (Malaclemys terrapin)

The Diamondback terrapin (Malaclemys terrapin) is a brackish-water turtle species whose populations have been fragmented due to anthropogenic activity such as development of coastal habitat and entrapment in commercial blue crab (Callinectes sapidus) fishing gear. Genetic analyses can improve conservation efforts for the long-term protection of the species. We used microsatellite DNA analysis to investigate levels of gene flow among and genetic variability within 21 geographically separate collections of the species distributed from Massachusetts to Texas. Quantified levels of genetic variability (allelic diversity, genotypic frequencies, and heterozygosity) revealed three zones of genetic discontinuity, resulting in four discrete populations: Northeast Atlantic, Coastal Mid-Atlantic, Florida and Texas/Louisiana. The average number of alleles and expected heterozygosity for the four genetic clusters were NA = 6.54 and HE = 0.050, respectively. However, the geographic boundaries of the populations did not correspond to accepted terrapin subspecies limits. Our results illuminate not only the need to sample terrapins in additional sites, specifically in the southeast, but also the necessity for allowing uninterrupted gene flow among population groupings to preserve current levels of genetic diversity.

Hot spots and hot moments of diamondback terrapin road‐crossing activity

SummaryRoad mortality is a major component of human impacts on wildlife populations, and the pervasiveness of roads on the landscape presents a substantial challenge for managing those impacts. The feasibility of methods to reduce road mortality depends on the degree to which this threat is spatially or temporally concentrated, which can be based on habitat, human activities or species' ecology. Diamondback terrapinsMalaclemys terrapinare a species of conservation concern across their range, and road mortality is a major threat contributing to local population declines.We used intensive road surveys of the 8·7‐kmDowning‐MusgroveCauseway toJekyllIsland,Georgia,USA, over 2 years to determine whether road activity and mortality was diffused or concentrated spatially (hot spots) or temporally (hot moments) in order to guide efficient management.In 2009 and 2010, we documented 636 terrapin crossings that were temporally and spatially condensed. Temporally, there was a 70–80% chance of a terrapin occurring on the road within a 3‐h period around the diurnal high tide and within the first 30 days of the ˜75 day nesting season. Over the two nesting seasons, 52% of terrapin occurrences on the road occurred within the 3‐h period around high tide. Spatially, 30% of terrapins were observed crossing in three hot spots that composed less than 10% of the length of the entire causeway, and the percentage of unvegetated high marsh was negatively associated with the number of terrapins that occurred on a section of road.Synthesis and applications. Our results demonstrate that hot spots and hot moments can be identified for species at finer scales than those found by other studies and are related, strongly or weakly, to specific temporal processes or habitat features. We found patterns of road mortality, like most threats, can be diffused or concentrated; therefore, complementary management tools that focus on hot spots or moments and also address the more diffused component of road mortality will be required to reduce this threat for at‐risk wildlife.

Estimating the consequences of multiple threats and management strategies for semi‐aquatic turtles

Summary Roads are pervasive fixtures on most landscapes but are typically among many factors contributing to wildlife population declines. Addressing road mortality as part of larger conservation efforts is challenging because it can be difficult to measure per capita mortality from roads and other concurrent threats. We used 4 years of mark–recapture–recovery data for diamondback terrapins Malaclemys terrapin on a causeway in Georgia, USA, to directly estimate threats of adult road mortality and nest predation, contrast the consequences to population growth using stage‐based matrix models and make management recommendations to stabilize the population. Mean estimated annual adult road mortality was 11·1% (range = 4·4–16·4%). Estimated annual nest predation was 61·9%. We estimated that the population was declining (λ &lt; 0·98) in all scenarios where both threats were included. Variation in adult survival was the most influential (highest elasticity) contributor to population growth relative to other demographic rates; however, λ would remain below 1 with any nest predation rate exceeding our estimate even if actions to mitigate road mortality were 100% effective. Synthesis and applications. Our study provides some of the first direct estimates of vehicle mortality rates and shows that mortality can remain sufficiently high among years to cause population declines. We also demonstrate that management actions focused on singular threats are inadequate for recovering populations. We conclude that integrated road and predator management is necessary to conserve turtle populations, and we suggest alternative strategies to compensate for some vehicle mortality and nest depredation.

Total body water and water turnover rates in the estuarine diamondback terrapin (Malaclemys terrapin) during the transition from dormancy to activity.

Water and salt concentrations in an animal's body fluids can fluctuate with changing environmental conditions, posing osmoregulatory challenges that require behavioral and physiological adjustments. The purpose of this study was to investigate body water dynamics in the estuarine diamondback terrapin (Malaclemys terrapin), a species that undergoes seasonal dormancy in salt marsh habitats. We conducted a field study to determine the total body water (%TBW), water turnover rate (WTR) and daily water flux (DWF) of female terrapins in south eastern North Carolina pre- and post-emergence from winter dormancy. Terrapins were injected with [(2)H]deuterium on two occasions and washout of the isotope was monitored by taking successive blood samples during the period of transition from dormancy to activity. The WTR and DWF of dormant terrapins were significantly lower than those of active terrapins (WTR(dormant)=49.70±15.94 ml day(-1), WTR(active)=100.20±20.36 ml day(-1), DWF(dormant)=10.52±2.92%TBW day(-1), DWF(active)=21.84±7.30%TBW day(-1)). There was no significant difference in %TBW between dormant and active terrapins (75.05±6.19% and 74.54±4.36%, respectively). The results from this field study provide insight into the terrapin's ability to maintain osmotic homeostasis while experiencing shifts in behavioral and environmental conditions.

Dispersal Behavior of Diamond-Backed Terrapin Post-Hatchlings

Post-emergence dispersal behavior of hatchling turtles has been investigated in several species, and a variety of species-specific orientation patterns have been reported. In the current study, we examined the orientation and dispersal behavior of hatchling, post-hatchling, and yearling Malaclemys terrapin pileata (Mississippi Diamond-backed Terrapin) by utilizing an orientation arena on two natural nesting beaches. Each age group displayed strong orientation and dispersal towards high-marsh vegetation instead of open water. The results suggest an innate behavior in young Diamond-backed Terrapins in which they orient from open beach areas toward vegetated marsh areas. The results also stress the importance of having healthy marsh habitat adjacent to nesting areas to provide critical habitat for these vulnerable life-history stages of Diamond-backed Terrapins.

Recreational Boats and Turtles: Behavioral Mismatches Result in High Rates of Injury

Recreational boats are a dominant feature of estuarine waters in the United States. Boat strike injury and mortality may have a detrimental effect on populations of diamondback terrapins (Malaclemys terrapin), a keystone species in estuarine ecosystems. In Barnegat Bay, New Jersey, 11% of terrapins (n = 2,644) have scars consistent with injuries from boats. Conservative estimates of injury rates from boats increased from 2006 to 2011. When exposed to playback recordings of approaching boat engines of varying sizes and speeds in situ, terrapins did not significantly change their behavior in response to sounds of boat engines of different sizes. The lack of behavioral response of terrapins to boat sounds helps explain high rates of injury and mortality of terrapins and may threaten the viability of terrapin populations. Boater education courses that discuss impacts of boats to wildlife, combined with closure of areas of high terrapin densities to boating, are necessary to protect terrapins and other aquatic species from injury and mortality caused by motorized boats.

Distribution of the Ornate Diamondback Terrapin (Malaclemys terrapin macrospilota) in the Big Bend Region of Florida

Little is known about the Ornate Diamondback Terrapin (Malaclemys terrapin macrospilota) from the Big Bend region of Florida (Wakulla, Jefferson, Taylor, and Dixie counties), and only 12 museum specimens from this area are known. We surveyed for this ecologically significant coastal species from the St. Marks River south for approximately 135 km to the Suwannee River in order to identify populations, locate and assess nesting habitats, create distribution maps for the species, and offer management recommendations to improve terrapin conservation in the Big Bend region. Using modified crab pots, head counts, and land surveys, we documented 37 new site records for Ornate Diamondback Terrapins. We captured 5 live terrapins, and recorded 5 heads, 6 intact nests, 16 crawls, terrapin material from 48 individuals, and 453 depredated terrapin nests. This survey documents the importance of the Big Bend region as significant habitat for this imperiled species. Managers should evaluate proposed development projects along this coastline for potential impacts to terrapin habitat and populations. We also recommend continued surveys of potential Diamondback Terrapin habitat along the Gulf coast of Florida so that additional populations can be located. We suggest that field studies commence at the terrapin population centers/nesting sites that we identified at Big Grass Island and vicinity, islands at the mouth of the Suwannee River, and areas surrounding the mouths of both the Steinhatchee and St. Marks rivers.