West Mojave Plan FEIR/S - Desert Managers Group

Pinto Mountain, with the highest coefficient of variation (26.69), the density estimate of 10.31tortoises/km 2 has a possible range of 6.12 to 17.38 tortoises/km 2 . The variation becomesimportant when one considers the large size of the regions involved.The high degree of variation is primarily due to small sample size, in this case, one year.As such, it is too soon to interpret the distance sampling data for the West Mojave, as the densityestimates derived from one year are far too variable. Relatively accurate density estimates maynot be available until completion of the fifth consecutive year 4 .Desert Tortoise Sign Count Surveys (1975 - 2002): Unlike the study plot (markrecapture)and distance sampling methodologies, sign count surveys are focused on tortoise scatand burrows rather than animals. Dr. Berry coordinated most of the earliest surveys in the mid-1970s until the late 1980s; LaRue coordinated the same-method surveys between 1998 and2002 5 .Between about 1988 and 1998, most sign count surveys were performed on militaryinstallations. BLM public lands had not been surveyed for nearly 20 years. The most recentBLM sign count surveys had been conducted between 1975 and 1982 when 1,678 transects weresurveyed within the CDCA, including 894 transects within the West Mojave planning area (seeBLM 1999). In 1990 a BLM survey was conducted over a 150 square mile area at a density ofthree transects per square mile, throughout the DTNA, Fremont Valley, and Spangler Hills(including portions of the BLM Open Area).The maps published in Berry and Nicholson (1984) were the most recent geographicportrayal of tortoise densities and distribution on public lands outside installations, until 1998,when new sign count surveys were conducted (Map 3-6). However, the 1984 range map (Map 3-7) was based, in part, on the early BLM surveys, and there have been documented declines intortoise numbers in much of the West Mojave since the data were collected (Berry 1990, asamended; Corn 1994).The data were used to identify only the relative abundance of tortoises (as judged by highversus low sign counts) and general distribution, given the imprecision inherent in using signcount data to determine tortoise densities (see Appendix L), rather than precise tortoise numbers.The results presented throughout this analysis equate each transect with one square mile (i.e.,4 In Washington County, Utah, in support of the Washington County HCP at the Red Cliffs Desert Reserve, AnnMcLuckie has supervised distance sampling over a consecutive five-year period, from 1998-2002. Looking at anygiven year, the coefficient of variation for Zone 3, for example, ranged from 15.86 up to 18.16 (McLuckie et al.2002). However when the data are combined over the four-year period, the pooled coefficient of variation wasgiven as 7.34, which a little more than two times more accurate than the estimates given for any one year.5 Methodologies used between 1975 and 2002 were essentially the same (Berry and Nicholson 1984), where onetransect was surveyed along a 1.5-mile equilateral triangle on a given square mile. The focus of the surveys hasalways been tortoise sign (hence, “sign count” surveys), although incidental sightings of live animals and carcasseswere also recorded. Observable human disturbances were also tallied along each sign count transect. Disturbancedata collected since 1998 have included: vehicles (paved roads, dirt roads, trails, tracks), garbage, shooting(shooting areas, individual shell casings), mining (test pits, markers), campsites, sheep sign, cattle sign, domesticdog sign, fence lines and posts, utility lines, denuded habitat, partially denuded habitat, old buildings, and ordnance.Chapter 3 3-80