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Population Status and Demographics of the Texas Diamondback Terrapin


The purpose of this study was to determine the abundance and movement of diamondback terrapins in Galveston Bay. The primary objectives were to determine 1) range and distribution of terrapin within the Galveston Bay system, 2) density and most probable population size of terrapins in Galveston Bay, 3) short-term and annual movement of terrapins, 4) habitat preferences of terrapins, and 5) relative magnitude of various sources of human induced mortality on terrapins.

Study Area

Galveston Bay and adjacent areas

Project Period

2010 – 2011

Project Description

The diamondback terrapin is the only turtle species to live exclusively in brackish water. Due to their limited distribution and unique life history, the Texas subspecies (Malaclemys terrapin littoralis) may be in danger of local extinction. Various sources of mortality have been identified including habitat loss, crab trap bycatch, power plant intakes, vehicular impacts and boating impacts. Little information has been gathered on the numbers or health of local Texas populations. The exact impact of natural occurrences, such as Hurricane Ike, which struck Galveston Island in September 2008, is unknown. This research will build upon previous research conducted by EIH on the population of the Texas diamondback terrapin by expanding the scope of the study to adjacent areas within Galveston Bay and adjacent sites to gather additional population and demographic data on these terrapin.

Publications and Presentations

Clarkson, E. 2012. Short term temporal trends in activity and habitat selection of the Texas diamondback terrapin. University of Houston-Clear Lake, Houston.

Clarkson, E. and Guillen, G. 2012. Small-scale habitat selection and activity trends of the diamondback terrapin in West Galveston Bay, Texas as determined by acoustic telemetry. In American Society of Ichthyologists and Herpetologists, Vancouver, BC. Poster.

Haskett, K. 2011. Abundance and movement of the Texas diamondback terrapin in the Deer Island Complex, Galveston, Texas. University of Houston-Clear Lake, Houston.

Marlow, A. and Guillen, G. 2011. Injury rates of diamondback terrapin (Malaclemys terrapin) in Galveston Bay, Texas. In Diamondback Terrapin Working Group. Poster.

Wrast, J., Guillen, G., Mokrech, M., and McCarthy, E. 2011. Development of a habitat suitability index for the Texas diamondback terrapin, Malaclemys terrapin littoralis. In Restore America's Estuaries, Galveston, TX. Poster

Clarkson, E., Marlow, A., and Guillen, G. 2010. Site fidelity and range of an island population of diamondback terrapin (Malaclemys terrapin) in West Galveston Bay, Texas. In Diamondback Terrapin Working Group. Poster.

Haskett, K. and Guillen, G. 2010. Population characteristics of diamondback terrapin at the Deer Island Complex; Galveston Texas during 2008. EIH Technical Report 10-017:37.

Project Sponsors