Ecology of the Diamondback Terrapin: Demographics, Movements, and Habitat Use
In response to declining populations, researchers at WARC are collecting data on demographics, movement patterns and habitat use, ecological niche and foraging ecology, and nesting ecology of diamondback terrapins.
The Science Issue and Relevance: The diamondback terrapin (Malaclemys terrapin) is a relatively small turtle that is the only estuarine turtle species in the United States (U.S.). It is considered a keystone species for salt marsh habitat because it helps maintain populations of the periwinkle snail (Littoraria irrorate), a herbivore that has the potential to over-graze salt marsh vegetation. Terrapins are distributed along the U.S. Atlantic and Gulf of Mexico coasts from Massachusetts to Texas. Listed as vulnerable on the International Union of Conservation (IUCN) Red List, terrapin populations are declining throughout their range due to overexploitation in the pet trade, road mortality, and drowning in crab traps. Loss of habitat from sea level rise and human development of coastal areas has also contributed to fragmented terrapin populations.
Life history attributes of terrapins, such as low reproductive rates and delayed sexual maturity, increase their vulnerability to environmental and anthropogenic (human-caused) disturbances. However, these life history attributes, along with behaviors and trends in abundance, vary among populations and this variation can complicate our understanding of population-specific conservation needs. Populations differ genetically, phenotypically, and geographically, so using data from one group to develop demographic models for another is not ideal. Additionally, understanding life-stage based survival of imperiled species populations is a valuable tool for managers and allows them to focus conservation efforts on individuals that will provide the greatest contribution to species recovery.
Animal movement and habitat use data for populations are also necessary for defining effective conservation strategies for species of concern. This is particularly critical for imperiled and exploited species that inhabit at-risk systems such as seagrass meadows and wetlands. Movement data for marine turtles has primarily been gathered through satellite and acoustic telemetry. While these techniques are ideal for large turtles that use relatively deep water (>1m) habitats, historically, they have not been adequate for smaller turtle species such as terrapins that predominately use shallow water habitats. It has always been assumed that terrapins remain in shallow water, therefore home range and movement data for that species have primarily been gathered by use of very high frequency (VHF) radio telemetry and mark-recapture methods. Results of those studies suggested terrapins moved <10 km from their capture sites and used home ranges that were generally <1 km2. However, VHF telemetry and mark-recapture methods have biases; particularly, they are limited to areas searched by surveyors. Recent advances in satellite tag technology have resulted in tags small enough to use on large terrapins. Results of satellite tracking suggests terrapins in northwest Florida use deeper water habitats and as such, could be detected using acoustic telemetry.
The objectives of this research project are to characterize the following aspects of terrapin population ecology in the southeastern U. S.:
- Demographics including apparent survival, relative abundance, reproductive output, and growth through mark-recapture and citizen science surveys
- Movement patterns and habitat use through satellite and acoustic telemetry
- Ecological niche and foraging ecology through use of stable isotope analyses
- Nesting ecology through citizen science
Methodology for Addressing the Issue: We conduct surveys for terrapins at our study sites in the northern Gulf of Mexico each year from April through November. All captured terrapins are weighed, measured, sexed, and aged. To allow individual identification, we give all captured terrapins a unique code that is notched into their marginal scutes. We also insert a passive integrated transponder (PIT) tag behind the left bridge of each terrapin after first cleaning the application site with isopropyl alcohol. Capture-recapture data resulting from these efforts are examined using a variety of population modeling methods (see Catizone et al. in review).
A subset of adult female terrapins receives a satellite tag, and a separate subset of adult female and adult male terrapins receives an acoustic tag. Telemetry tags are adhered to the carapace using slow-setting epoxy; satellite tags are placed on the anterior portion of the carapace whereas acoustic tags are placed on the posterior. The combined mass of the tag and epoxy is less than 5% of terrapin weight. We release tagged individuals at the site of capture. Telemetry data are analyzed using a variety of methods including home range analyses and site fidelity.
A skin sample is collected from each captured terrapin for stable isotope analyses to examine foraging ecology, niche use, and diet. To analyze stable isotope data in the context of isotopic niche width among species, we adopt the metrics based in a Bayesian framework. Potential prey items, such as periwinkle snails, mangrove leaves, and fish, are also collected to inform Bayesian mixing models. Variations in prey use and niche metrics by terrapin size, sex, year, and other variables are also examined.
Future Steps: We are partnering with several researchers and agencies to improve the design of satellite tags for use with small turtle species such as terrapins. The ultimate goal is a tag that can remotely transmit global positioning system (GPS) quality locations and is small enough for a terrapin or similarly sized turtle to safely carry.
In response to declining populations, researchers at WARC are collecting data on demographics, movement patterns and habitat use, ecological niche and foraging ecology, and nesting ecology of diamondback terrapins.
The Science Issue and Relevance: The diamondback terrapin (Malaclemys terrapin) is a relatively small turtle that is the only estuarine turtle species in the United States (U.S.). It is considered a keystone species for salt marsh habitat because it helps maintain populations of the periwinkle snail (Littoraria irrorate), a herbivore that has the potential to over-graze salt marsh vegetation. Terrapins are distributed along the U.S. Atlantic and Gulf of Mexico coasts from Massachusetts to Texas. Listed as vulnerable on the International Union of Conservation (IUCN) Red List, terrapin populations are declining throughout their range due to overexploitation in the pet trade, road mortality, and drowning in crab traps. Loss of habitat from sea level rise and human development of coastal areas has also contributed to fragmented terrapin populations.
Life history attributes of terrapins, such as low reproductive rates and delayed sexual maturity, increase their vulnerability to environmental and anthropogenic (human-caused) disturbances. However, these life history attributes, along with behaviors and trends in abundance, vary among populations and this variation can complicate our understanding of population-specific conservation needs. Populations differ genetically, phenotypically, and geographically, so using data from one group to develop demographic models for another is not ideal. Additionally, understanding life-stage based survival of imperiled species populations is a valuable tool for managers and allows them to focus conservation efforts on individuals that will provide the greatest contribution to species recovery.
Animal movement and habitat use data for populations are also necessary for defining effective conservation strategies for species of concern. This is particularly critical for imperiled and exploited species that inhabit at-risk systems such as seagrass meadows and wetlands. Movement data for marine turtles has primarily been gathered through satellite and acoustic telemetry. While these techniques are ideal for large turtles that use relatively deep water (>1m) habitats, historically, they have not been adequate for smaller turtle species such as terrapins that predominately use shallow water habitats. It has always been assumed that terrapins remain in shallow water, therefore home range and movement data for that species have primarily been gathered by use of very high frequency (VHF) radio telemetry and mark-recapture methods. Results of those studies suggested terrapins moved <10 km from their capture sites and used home ranges that were generally <1 km2. However, VHF telemetry and mark-recapture methods have biases; particularly, they are limited to areas searched by surveyors. Recent advances in satellite tag technology have resulted in tags small enough to use on large terrapins. Results of satellite tracking suggests terrapins in northwest Florida use deeper water habitats and as such, could be detected using acoustic telemetry.
The objectives of this research project are to characterize the following aspects of terrapin population ecology in the southeastern U. S.:
- Demographics including apparent survival, relative abundance, reproductive output, and growth through mark-recapture and citizen science surveys
- Movement patterns and habitat use through satellite and acoustic telemetry
- Ecological niche and foraging ecology through use of stable isotope analyses
- Nesting ecology through citizen science
Methodology for Addressing the Issue: We conduct surveys for terrapins at our study sites in the northern Gulf of Mexico each year from April through November. All captured terrapins are weighed, measured, sexed, and aged. To allow individual identification, we give all captured terrapins a unique code that is notched into their marginal scutes. We also insert a passive integrated transponder (PIT) tag behind the left bridge of each terrapin after first cleaning the application site with isopropyl alcohol. Capture-recapture data resulting from these efforts are examined using a variety of population modeling methods (see Catizone et al. in review).
A subset of adult female terrapins receives a satellite tag, and a separate subset of adult female and adult male terrapins receives an acoustic tag. Telemetry tags are adhered to the carapace using slow-setting epoxy; satellite tags are placed on the anterior portion of the carapace whereas acoustic tags are placed on the posterior. The combined mass of the tag and epoxy is less than 5% of terrapin weight. We release tagged individuals at the site of capture. Telemetry data are analyzed using a variety of methods including home range analyses and site fidelity.
A skin sample is collected from each captured terrapin for stable isotope analyses to examine foraging ecology, niche use, and diet. To analyze stable isotope data in the context of isotopic niche width among species, we adopt the metrics based in a Bayesian framework. Potential prey items, such as periwinkle snails, mangrove leaves, and fish, are also collected to inform Bayesian mixing models. Variations in prey use and niche metrics by terrapin size, sex, year, and other variables are also examined.
Future Steps: We are partnering with several researchers and agencies to improve the design of satellite tags for use with small turtle species such as terrapins. The ultimate goal is a tag that can remotely transmit global positioning system (GPS) quality locations and is small enough for a terrapin or similarly sized turtle to safely carry.