West Mojave Plan FEIR/S - Desert Managers Group

of the Johnson Valley Open Area, and the fourth animal was observed about seven miles southof the open area. Two were within higher sign count areas, and the other two were within two tothree linear miles. None was within recent die-off areas; the closest was in the southern portionof the Ord-Rodman DWMA, approximately three miles northwest of the nearest die-off region.Summary of All Carcass Observations: Table L-11 (see Appendix L) summarizes thecumulative findings listed above. Region-wide, there were of 420 mi 2 of die-offs, including 279mi 2 (66%) of newer die-offs and 141 mi 2 (34%) of older die-offs; given the overlap of 29 mi 2 ,there were a total of 391 mi 2 affected by both newer and older die-offs. This indicates that about3.5% of the 2002 tortoise range (391 of 11,134 mi 2 ), or 11.6% of the surveyed area (391 of 3,362mi 2 ), were within older and newer die-off regions.A total of 600 carcasses were found within the die-off regions (59% of the 1,011carcasseswhere coordinate information was available), including 388 (65%) newer carcasses and 212(35%) older carcasses. This is a significant finding, indicating that tortoises are continuing to diethroughout the planning area, particularly in the Superior-Cronese DWMA, probably since about1990. Newer die-off regions were characterized by 317 (85%) newer carcasses and 54 (15%)older carcasses; older die-off regions were characterized by 158 (69%) older carcasses and 71(31%) newer carcasses. These latter findings suggest that tortoises continue to die in older dieoffregions, even though older carcasses were twice as likely to be found as newer ones.3.3.2.6 Tortoises and Off Highway VehiclesOne of the most controversial resource management issues within the western MojaveDesert concerns the relationship between desert tortoises and off-highway motorized vehicles.This discussion will address both casual OHV use and competitive events and the effects thatboth may, or may not, have on tortoises and habitat.3.3.2.6.1 Dispersed Casual OHV UseOff highway vehicles users visit the desert for many purposes. They explore the desert,hunt, and drive to campsites and trailheads for hiking or horseback riding, rockhounding andother activities. Commercial uses are also common, for mineral exploration, maintenance ofexisting facilities, and administrative or law enforcement purposes. This use occurs in a moredispersed manner than, for example, concentrated competitive events, and results in a lowdensitybut continuing presence of vehicles throughout the desert. The following discussionaddresses effects that have occurred as a consequence of such dispersed, casual use of theplanning area by off highway vehicles.Boarman (2002) conducted a literature review of 56 references that addressed OHVbasedimpacts on desert tortoises. His conclusion follows:Although each study comparing tortoise densities inside and outside of [OHV] areas haslimitations, they all lend evidence to reductions in tortoise population densities in heavy [OHV]use areas. The causes for these declines are less certain. Tortoises and their burrows are crushedby [OHVs], although it is difficult to evaluate the full impact this activity currently has on tortoiseChapter 3 3-119