Resource Brief: Texas Tortoise Program Summary
Carlson JE. 2022. Resource Brief: Texas Tortoise Program Summary. Gulf Coast I&M Network
This 2-page brief summarizes how the Gulf Coast Network monitors the Texas tortoise population at Palo Alto Battlefield National Historical Park. The primary monitoring technique is a long-term mark-recapture study where the network crew visits the park in the fall of each year and conducts time and area constrained searches for tortoises in seven permanent sampling units. These units encompass most of the park's major lomas, which are low-rising ridges covered in thorny shrublands and are known to be the tortoises' preferred habitat in coastal Texas. As the crew encounters tortoises during the surveys, they weigh them, measure their carapace dimensions, photograph them, and record the sex, overall condition and GPS location. For newly-encountered individuals, they drill holes in marginal scutes according to a unique numeric code, so they can be identified upon recapture. The sampling visits are 3-4 days long and consist of each unit being search twice, for roughly 2 hours each time, on two different days and by two different teams. The total area covered per visit is 28 hectares of preferred tortoise habitat, and the total effort per visit is 108 person-hours. The objectives of this long-term monitoring study are: 1) To provide a detailed depiction of the status of Texas tortoises across the park’s major lomas, including catch per unit effort , within-park movements, body condition and the distribution of sizes and sexes captured. Catch per unit effort and tortoise body condition are also analyzed for change over time. 2) To assess tortoise population parameters across the park’s major lomas and track how these parameters change over time, including estimated abundance and survivorship from mark-recapture data.