West Mojave Plan FEIR/S - Desert Managers Group

“52 mi 2 of higher density tortoise areas,” “12 mi 2 of higher density vehicle-based impacts,” etc.).Dr. Krzysik has calculated that each sign count transect is sufficient to survey about 1.3% of agiven square mile. As such, data collected along transects are best used as an index, not anabsolute census of the population or its characteristics. Data from any one or two transectswould have very low predictive value for the square mile(s) being characterized.However, importantly, on a regional scale when all transects are combined, distributionpatterns and relative occurrences (i.e., “above” versus “below” average concentrations) oftortoises are revealed. And even more importantly, they are corroborated by distance samplingdata, and are consistent with trends reported on Dr. Berry’s study plots.Sign count survey data were used to: (a) refine proposed DWMA boundaries (e.g.,determine whether DWMA status was appropriate for the Iron Mountains, an area outside ofcritical habitat and north of Helendale/Silver Lakes where surveys identified significant amountsof tortoise sign); (b) determine the best places to close routes to minimize impacts in areas wheretortoises most likely occur; and (c) determine alternative DWMA boundaries and compare EIR/Salternatives.Sign count surveys conducted since 1988 (see Map 3-6) provide the most recent,available data on the distribution of tortoise sign, which Dr. Anthony Krzysik (2002a, b, c) hasshow to be positively correlated to incidence of tortoises. Over 8,100 transects have beensurveyed on more that 6,300 square miles within the West Mojave planning area. These surveyefforts are summarized in Appendix LMost of the best available data on current tortoise distribution and observable humandisturbances are encompassed in the 1998, 1999, and 2001-2002 data sets, when 3,372 transectswere surveyed for the West Mojave planning effort. Relevant information is described below:• 1998 West Mojave Regional Survey: This was the first regional sign count surveyundertaken on BLM lands in the western Mojave Desert in nearly 20 years. Surveyswere completed between July and September 1998 on 856 square miles.• 1999 West Mojave-Fort Irwin Regional Survey: Conducted under the direction of theBLM, USFWS, and Army, biologists surveyed various Fort Irwin expansion alternativeareas and remaining portions of the planning area, particularly in proposed DWMAs.Between July and September 1999 biologists surveyed 1,553 transects on 1,291 squaremiles around Fort Irwin and California City, among other places.• 2001-2002 West Mojave Regional Survey: Biologists surveyed BLM lands within theplanning area that were not surveyed in 1998 and 1999, might support significantaggregations of tortoises outside the proposed DWMAs (such as Searles, Indian Wells,and Rose valleys to the north), and could confirm areas of expected low-density (areaencompassed by I-15, I-40, Troy Dry Lake, and the eastern planning boundary).Between July 2001 and January 2002, a total of 1,329 square miles meeting one or moreof these criteria was surveyed.Chapter 3 3-81