West Mojave Plan FEIR/S - Desert Managers Group

Table 3-22Characteristics of Older and Newer Die-Off Regions in theSuperior-Cronese DWMAREGION NO. & AGE OF NO. MI 2 NO. RANGENAMEDIE-OFFCARCASSESAVERAGE(Carc/mi 2 )SC1. N of Harper Newer 27 29 1 to 4 1.1SC2. Coolgardie Mesa Newer 22 24 1 to 4 1.1SC3. Hinkley Newer 11 13 1 to 3 1.2SC4. N of Barstow Newer 10 13 1 to 2 1.3Subtotal 4 Newer 70 79 1 to 4 1.2SC5. E Superior Valley/ Newer 23 35 1 to 4 1.5Goldstone Older 5 8 1 to 3 1.6Subtotal 1 Older/1 Newer 28 43 1 to 4 1.6SC6. Coyote Corner/Newer 56 99 1 to 8 1.8Paradise Valley Older 7 26 1 to 8 3.7SC7. Alvord Slope Newer 16 27 1 to 5 1.7SC8. Cronese Lakes Older 6 8 1 to 3 1.3TOTALSOlderNewer18 (10%)165 (90%)42 (15%)240 (85%)1 to 81 to 8Observations: The three older die-off subregions were all relatively small (i.e., between 5mi 2 and 7 mi 2 ), encompassed 18 mi 2 , where 42 (15% of 282) carcasses found had died more thanfour years ago 15 . The seven older die-off subregions were all relatively large (i.e., between 10mi 2 and 56 mi 2 ), encompassed 165 mi 2 , where 240 (85% of 282) tortoises had died within fouryears of being found. As such, both older and newer die-off regions encompassed about 19%(183 mi 2 of 980 mi 2 ) of the Superior-Cronese DWMA. Whereas 19% may seem like aninsignificant amount of land for this large, 980 mi 2 area, the spatial distribution (Map 3-13) wasthroughout the DWMA north of Highway 58, and all higher density live tortoise areas wereproximate.Only 18 mi 2 (10%) of the Superior-Cronese were indicative of older die-off regions. Allcarcasses in the remaining 165 mi 2 (90%) had died within four years of being found. Region SC8was the only older region not associated with a more recent die-off. The other two older regions(i.e., SC5 and SC6) were encompassed within predominantly recent die-off areas. Unlike theFremont-Kramer, which is characterized as an older die-off region (170 of 223 carcasses, or76%), the Superior-Cronese is a region of predominantly newer die-offs (i.e., 240 of 282carcasses, or 85%), where most observed tortoises had died since about 1990.BLM Study Plots: None of the nine permanent study plots is within the Superior-CroneseDWMA (i.e. six are within the Fremont-Kramer and three are within or adjacent to the Ord-Rodman DWMA). Had plots been established in the Superior-Cronese, there may have been anopportunity to detect these recent die-offs earlier, as Dr. Berry had done in the Fremont-KramerDWMA. Establishing study plots in remaining portions of higher density tortoise areas may beprudent to detect die-offs as they occur, rather than after the fact.15Time since death is only a relative indicator. Taken literally, it would mean that the tortoises died between 1994and 1997, relative to the survey dates of 1998 and 2001. It is a safer assumption that these tortoises died sometimeafter 1990.Chapter 3 3-1172.21.4