Twenty-Fourth Annual Meeting and Symposium of the Desert Tortoise Council, March 5-8, 1999
Abstracts

Between 1996 and 1998, we established 20 plots within the National Training Center (NTC), Fort Irwin, in San Bernardino County, California. Research objectives were site- or region-specific and included: (1) characterization of demographic attributes of tortoises, (2) assessment of health and presence of mycoplasmosis and shell diseases, (3) evaluation of location for suitability for translocated tortoises, and (4) assessment of potential for critical habitat. The health and demographic attributes of populations differed by site and region, and depended on such factors as geographic location and history of human use. Two of the 20 plots (2.25 km² each) are within the Superior-Cronese critical habitat on the north Alvord Slope and have been protected from military vehicle use by a fence since 1994. Densities range from 6 to 17 tortoises/km². Subadult and adult tortoises on both plots experienced higher annual death rates (>5%) between 1993 and 1997 than reported for stable populations. Significantly fewer live tortoises were found near the fence and the military training area than in less disturbed areas away from the fence. We tested 17 of the 44 tortoises captured for Mycoplasma agassizii and M. nov. sp., the pathogens responsible for upper respiratory tract disease (URTD). None of the tortoises tested positive for the pathogen. In previous years, Jacobson et al. (1996) reported tortoises with positive ELISA tests (12.5%, N = 32) from the North Alvord Slope.

Three of the 20 plots are in military training areas (Tiefort Mountains, Eastgate 1 and Eastgate 2). The Tiefort Mountains plot (4.6 km² in size), the site for which we have the most complete population data, has a density of 28 tortoises/km² and experienced an annual death rate of 1.9% for subadult and adult tortoises between 1992 and 1997. Tortoises at the Tiefort and Eastgate sites were tested for mycoplasma using the ELISA test, polymerase chain reaction technique, and cultures. The 81 sets of samples were negative.

The 15 plots (1 km² each) at the Goldstone Deep Space Communications Center were in areas protected from military training exercises. Densities were low, estimated at 1-5 tortoises/km² overall. A total of 17 live tortoises and 135 shell-skeletal remains were found on the plots. Approximately 80 of the 135 shell-skeletal remains represent tortoises that died between 1994 and 1998. Of 9 tortoises tested for mycoplasmosis, 2 (22%) were positive with the ELISA test. Shell disease was common in the tortoises at Goldstone and the NTC.

Literature Cited

Jacobson, E. R., M. B. Brown, P. A. Klein, I. Schumacher, D. Morafka, and R. A. Yates. 1996. Serologic survey of desert tortoises, Gopherus agassizii, in and around the National Training Center, Fort Irwin, California, for exposure to Mycoplasma agassizii and the causative agent of upper respiratory tract disease. Proc. Desert Tortoise Council Symp. 1996:53-54.