West Mojave Plan FEIR/S - Desert Managers Group

Rodman DWMA. There were no higher density areas in El Mirage, although the survey effortwas relatively light, and 5 mi 2 were found immediately northwest of Spangler Hills.Relative Tortoise Occurrence in Open Areas 17 : Tortoise encounters were the highest inStoddard Valley (i.e., 1 tortoise/10.5 linear miles of transects), intermediate in Johnson Valley(i.e., 1 tortoise/43.3 miles), and lowest in Spangler Hills (i.e., 1 tortoise/56.2 miles). El Miragewas relatively high (i.e., 1 tortoise/8.0 miles), but the sample size was sufficiently small that thiswas likely an artifact of the survey rather than a relative estimate of abundance.The data suggest the following descending order of tortoise abundance in the four openareas: Stoddard Valley > Johnson Valley > (El Mirage, suspected) > Spangler Hills.Collectively, 22 live tortoises were observed over 520 linear miles of transects in these four openareas, for an encounter rate of 1 tortoise/23.6 miles of transects. For comparison, 154 liveanimals were observed on 2,293.5 miles of transects in three DWMAs (i.e., excluding PintoMountain), for an encounter rate of 1 tortoise/14.9 miles, or about 1.6 times higher than in openareas.Relative Occurrence of Carcasses in Open Areas: Carcass encounters were the highestin Johnson Valley (i.e., 1 carcass/5.25 miles), intermediate at Stoddard Valley (i.e., 1carcass/8.59 miles), and lowest in Spangler Hills (i.e., 1 carcass/12.5 miles). El Mirage wasrelatively high (i.e., 1 carcass/4.8 miles), but again, sample size was too small to be meaningful.The data suggest the following descending order of carcass abundance in the four open areas:Johnson Valley > Stoddard Valley > (El Mirage, suspected) > Spangler Hills.Comparisons between Live Tortoises and Carcasses in Three Open Areas: The inverserelationship described previously for DWMAs was not observed in the three open areas. Table3-25 shows the encounter rates for both tortoises and carcasses.Table 3-25Tortoise and Carcass Encounter RatesAREA OF COMPARISON ONE TORTOISEOBSERVED EVERYONE CARCASS OBSERVEDEVERYStoddard Valley 10.5 mi 8.59 miJohnson Valley 43.3 mi 5.25 miSpangler Hills 56.2 mi 22.5 miObservations in three DWMAs (i.e., excluding Pinto Mountain) indicated an inverselinear relationship between live tortoises and carcasses; tortoises were more often encounteredwhere fewer carcasses were found. Observations in the Stoddard Valley Open Area followedthis pattern, but not for either Johnson Valley or Spangler Hills. Spangler Hills is relativelyeasily explained; very low encounter rates for both tortoises and carcasses suggests low densitiesof tortoises. Johnson Valley, however, appears to be an anomaly, as it was the only place wheretortoises were difficult to find, but carcasses were relatively easy. Only 10 sign count tortoises17 Appendix L shows encounter rates, carcass data and other calculations that were used in support of the aboveobservations.Chapter 3 3-129