Management and research of desert tortoises for the Yucca Mountain Project

A program has been developed for the Yucca Mountain Project (YMP) to manage and study the desert tortoise (Gopherus agassizi), a threatened species that occurs at low densities at Yucca Mountain. The goals of this program are to better understand the biology and status of the desert tortoise population at Yucca Mountain, assess impacts on tortoises of site characterization (SC) activities, and minimize those impacts. The first steps we took to develop this program were to compile the available information on the biology of tortoises at Yucca Mountain, ascertain what information was lacking, and identify the potential impacts on tortoises of SC. We then developed a technical design that can be used to identify and mitigate direct and cumulative impacts and provide information on tortoise biology. Interrelated studies were developed to achieve these objectives. The primary sampling unit for the impact monitoring studies is radiomarked tortoises. Three populations of tortoises will be sampled: individuals isolated from disturbances (control), individuals near major SC activities (direct effects treatment and worst-case cumulative effects treatment), and individuals from throughout Yucca Mountain (cumulative effects treatment). Impacts will be studied by measuring and comparing survival, reproduction, movements, habitat use, health, and diet of these tortoises. A habitat quality model also will be developed and the efficacy of mitigation techniques, such as relocating tortoises, will be evaluated.