28th Annual Meeting and Symposium of the
Desert Tortoise Council, February 21-23, 2003
Abstracts

Baseline Monitoring in the Upper Virgin River Recovery Unit

Ann M. McLuckie¹, Richard A. Fridell¹, Randy Radant², and Peggy Miller^2
1Utah Division of Wildlife Resources, 344 East Sunland Dr. #8, St. George, Utah 84790;
²Utah Division of Wildlife Resources, 1594 W. North Temple, P.O. Box 146301, Salt Lake City, Utah 84114

The Upper Virgin River Recovery Unit, managed as the Red Cliffs Desert Reserve, is considered a highly threatened population due to its proximity to urban growth and small size. The Reserve includes 38,787 acres of Mojave desert tortoise habitat and its goal is to maintain a stable or increasing tortoise population in perpetuity. The Reserve is located in southwest Utah, Washington County, within the Upper Virgin River Valley. The Reserve represents the northeastern extent of the desert tortoise's geographic distribution.

Accurate regional desert tortoise density estimates are a critical component of the Washington County HCP. The monitoring objective for the Reserve is to: 1) obtain precise and accurate baseline abundance and density estimates, and 2) assess long-term density and abundance trends over a 20 year period. The pooled density of adult tortoises in Zone 3, the core of the Reserve, was 0.32 tortoises per hectare (95%CI: 0.29-0.36; CV: 5.85%) while the pooled density across the Reserve was estimated at 0.29 tortoises per hectare (95%CI: 0.26-0.33; CV: 5.87%).

Several demographic parameters including growth rates and health assessments were observed as a byproduct of monitoring. In all years, growth rate of recaptured tortoises was significantly correlated with original capture CL with annual growth declining as CL increased. In 2001, the annual growth rate was significantly below the 95% confidence interval of 1998, 1999, and 2000 monitoring years.

Although URTD symptoms have been previously observed within the Reserve, a general increase in the percent of tortoises processed during monitoring has been observed since 1997. In the last three years precipitation in the St. George area has been well below the 50 year mean as well as the 95% confidence interval. If physiological stress exacerbates the signs of the disease, clinical symptoms would be expressed during these "stressful" or drought periods. Although health observations not only suggest the presence of URTD but a possible increase in tortoises with the disease, biological samples (e.g., blood, exudates, biopsy specimens) are required to confirm the pattern and magnitude of URTD occurrence within the Reserve.