A MARK-RECAPTURE STUDY OF THE DIAMONDBACK TERRAPIN (MALACLEMYS TERRAPIN) IN CHARLESTON HARBOR, SOUTH CAROLINA

Hannah Day1 and David Owens1

Currently the status of the Diamondback Terrapin, Malaclemys terrapin, is unknown or declining throughout much of its range. Due to the multitude of anthropogenic threats terrapins face, more research is needed to assess population trends. In this mark-recapture study, terrapins will be sampled using both trammel netting and seine netting. Captured individuals will be dual marked using PIT tags and marginal scute notching to evaluate the efficacy of PIT tagging as a viable mark-recapture technique for this species. The use of multiple capture techniques is designed to sample both Charleston Harbor sites and adjacent tidal creeks in order to look at seasonal shifts in habitat use. In addition, female reproductive condition will be assessed using ultrasound and used to explore links between habitat shifts and reproduction. Sex ratios will also be determined to look at potential differential mortality between sexes. Mark- recapture data will be used to generate a population size estimate for Charleston Harbor using MARK software. The Charleston Harbor population size will then be compared to estimates calculated for the Ashley River in 2010 to gain an understanding of patterns throughout the estuary. This information on population size, sex ratios, and habitat usage can be used to evaluate the status of terrapins in Charleston Harbor and ultimately help to determine if new management measures should be considered.

ABSTRACT Natural History of the Diamondback Terrapin1 -The only obligate estuarine turtle found in North America -Ranges from Cape Cod, MA to Texas -Heavily exploited through the early 20th century as a gourmet food item

Current Status -Believed to be declining throughout much of their range -Face many anthropogenic threats1,2,3 • Road mortality, habitat loss, drowning in crab pots -The status of the Diamondback Terrapin in South Carolina is unknown2

• Terrapins are currently a state-regulated species (Chapter 5 Section 50-5-2300) and considered high priority

• Declines have been documented in the Kiawah River3

Ecology and Reproduction -Sexually dimorphic1

-Display high site fidelity and small home ranges1,2

-Use different habitat types to complete life cycle4

• Foraging, mating, and nesting -May form dense aggregations in spring specifically for mating purposes6

1. Estimate the population size and sex ratio of

Diamondback Terrapins in Charleston Harbor using MARK analysis of mark-recapture data

2. Compare to population size determined for the Ashley River in 2010

3. Evaluate the efficacy of PIT tagging and marginal scute notching as mark-recapture techniques for terrapins How much PIT tag loss occurs in the wild? 4. Determine if terrapin populations undergo distinct seasonal habitat shifts -Assess using capture data and ultrasound Are shifts in habitat use related to reproduction?

OBJECTIVES

Capture methods -Capture via trammel net in conjunction with SCDNR Inshore Fisheries • Samples a random set of 12-14 sites throughout the

harbor each month • Effective for capturing terrapins along shorelines in

the harbor -Capture via modified seine net • More effective at sampling terrapins located within

tidal creeks

Tagging and morphometrics • Sex and morphometric data recorded • 11mm polymer PIT tag inserted into right rear leg • A unique series of 4 V-shaped notches are filed into

each turtle’s marginal scutes

Ultrasound • Reproductive structures of female terrapins imaged

using an Aloka 500 ultrasound equipped with a 5.0 MHz probe

Data Analysis -Population estimates using program MARK

METHODS

1. Brenessel, B. 2006. Diamonds in the Marsh: Natural History of the Diamondback Terrapin. Lebanon, NH: University Press of New England. 2. Gibbons, J.W et al. 2001. Demographic and Ecological Factors affecting conservation and management of the diamondback terrapin (Malaclemys terrapin) in South Carolina. Chelonian Conserv Bi, 4. 3. Dorcas, M.E. et al. 2007. Crab trapping causes population decline and demographic changes in diamondback terrapins over two decades. Biol Cons, 137. 4. Roosenburg, W.M. 1990. The Diamondback Terrapin: Population dynamics, habitat requirements, and opportunities for conservation. New Perspectives in the Chesapeake System: A Research and Management Partnership. Proceedings of a Conference. Chesapeake Research Consortium, 137. 5. Broyle, E. 2010. Diamondback Terrapins of Charleston, South Carolina: Population Estimate, Sex Ratios, and Distribution. M.S. Thesis. The Graduate School at the College of Charleston. Charleston, SC. 6. Estep, B. 2005. Seasonal movements and habitat use patterns of a diamondback terrapin population. M.S. Thesis. The Graduate School at the College of Charleston. Charleston, SC.

REFERENCES

I would like to thank my advisor, David Owens, and my committee members, Bill Roumillat, Erin Levesque and Pace Wilbur. Special thanks go to the SCDNR Inshore Fisheries Section, funded through NMFS Project NA08NMF4720514, for summer support and field assistance. I am also very grateful to my fellow students who volunteered their time for help with fieldwork.

ACKNOWLEDGEMENTS

a b

Fig 4. An ultrasound image displaying 2 eggs measured with digital calipers.

Fig 3a. Schematic of plastron length, carapace length, carapace width, and head width measurements taken on each turtle. Fig3b. Schematic of notching codes

-Population size in the Ashley River was estimated to be 3060 with a 95% confidence interval of 1964-4156 in 20105

• SCDNR incidental capture data predicts a smaller population in Charleston Harbor

-More trammel captures in Spring/early Summer; More seine captures in Fall • Leave tidal creeks for mating/nesting habitats and return to creeks for

foraging/hibernation habitats

PREDICTIONS

1. Graduate Program in Marine Biology, College of Charleston

Fig 2a. Map of sampling locations in Charleston Harbor. Red bull’s-eyes indicate trammel sites and yellow stars indicate tidal creek seine sites. Sampling for terrapins begins in March and goes through October. Fig2b. A male terrapin captured by trammel net. Fig2c. A typical seine pull in a tidal creek.

a b

c

INTRODUCTION

Fig 1. Comparison of the sexes