West Mojave Plan FEIR/S - Desert Managers Group

In October 2002, on a 100-acre site in eastern Twentynine Palms, four of five tortoises(including a hatchling and one-year old tortoise) were found in relatively thick growth of biggalleta (a perennial grass) alongside two intermittent streams (Circle Mountain BiologicalConsultants, 2002.). Scat and burrows were found throughout the site, but four of five tortoiseswere clearly associated with washes. More recently (November 2002) during a training exerciselocated west of California City and east of Highway 14, 11 tortoises were observed, 10 of whichwere located within or immediately adjacent to Cache Creek (LaRue, pers. obs).Based on the above observations, it is plausible that tortoises may concentrate aroundwashes during drought conditions, which would put them at heightened risk if vehicles wereconcurrently using the washes. In extreme conditions, presumably even the wash-adapted plantswill become dry. Given the relative denseness of the plant growth along washes, this may putthem at some heightened risk for vehicle-caused fires. Certainly, there is no way to avoiddrought, however restricting vehicle travel in washes may be the only mechanism available tominimize drought-related vehicle impacts to tortoises that are relying on washes for sustenanceand cover.Disease: Boarman (2002) provided the following summary on tortoise diseases (see hisliterature cited section for full references). Diseases can weaken individuals, reduce reproductiveoutput, and cause mortality. Epidemic outbreaks of some diseases can become catastrophic,particularly in small or declining populations (Dobson and Meagher 1996, Biggins et al. 1997,Daszek et al. 2000). Upper Respiratory Tract Disease (URTD; Jacobson et al. 1991) andcutaneous dyskeratosis affecting the shell (Jacobson et al. 1994) are the two diseases most oftenimplicated in tortoise declines. A third disease, a herpesvirus, was recently identified and mayhave population-level consequences, but very little is known about its relative mortality oninfected tortoises (Berry et al. 2002, Origgi et al. 2002).URTD has been found in several populations that have experienced high mortality rates,including some in the West Mojave (Jacobson et al. 1996, Berry 1997). Brown et al. (1994a)showed definitively that URTD could be caused by the bacterium, Mycoplasma agassizii. Asecond species, to be named “Mycoplasma cheloniae,” was found in 2001 in tortoises in northernLucerne Valley and at the DTNA (Kristin Berry, pers. comm.).URTD, also referred to as “mycoplasmosis,” is likely transmitted by contact with adiseased individual or through aerosols infected with M. agassizii or M. cheloniae. Theorganism attacks the upper respiratory tract causing lesions in the nasal cavity, excessive nasaldischarge, swollen eyelids, sunken eyes, and in its advanced stage, lethargy and probably death(Jacobson et al. 1991, Schumacher et al. 1997, Homer et al. 1998, Berry and Christopher 2001).It must be noted, however, that some of these clinical signs may also be characteristic of otherhealth conditions such as dehydration, allergy, or infection with herpesvirus or the bacteriaChlamydia or Pasteurella (e.g., Pettan-Brewer et al. 1996, Schumacher et al. 1997).Malnutrition is known to result in immunosuppression in humans and turtles (Borysenkoand Lewis 1979) and is associated with many disease breakouts. It is possible that nutritionaldeficiency in tortoises caused by human-mediated habitat change and degradation may be partlyresponsible for the apparent spread of URTD and its perceived impact on tortoise populationsChapter 3 3-110