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27th Annual Meeting and Symposium of the
Desert Tortoise Council, March 22-24, 2002
Abstracts
Implementation of the Line Distance Sampling Method Throughout the Mojave Desert in 2001
Philip A. Medica1, P. Stephen Corn2, and
Ronald W. Marlow3
1Desert Tortoise Recovery Coordinator, U.S. Fish and
Wildlife Service, 4701 N. Torrey Pines Drive, Las Vegas, Nevada
89130;
2U.S. Geological Survey, Missoula, Montana;
3University of Nevada-Reno, Las Vegas, Nevada
During the spring of 2001 rangewide Line Distance Sampling was initiated within every Desert Wildlife Management Area (DWMA) and several military installations and national parks. A total of nearly 3000 kilometers were walked and 572 live tortoises were observed, 219 of which were from the Virgin River Recovery Unit alone. From this first year sampling data the encounter rate for each DWMA or Critical Habitat area could be determined. Based upon the 2001 encounter rates observed we will upscale our sampling to include additional kilometers in 2002. Encounter rates varied from lows of 0.05 in Shadow Valley, California (in the northern portion of Ivanpah DWMA), and 0.06 in Beaver Dam Slope, and 0.10 in the Northeast Mojave DWMA, to highs of 0.70 in the Virgin River Recovery Unit (VRRU), Red Cliffs Desert Reserve, and 0.32 in parts of the Chuckwalla DWMA on Chocolate Mountain Gunnery Range. The overall mean encounter rate combining all the DWMAs sampled (excluding VRRU) was 0.13 rangewide. Preliminary results indicate that larger sample sizes of live desert tortoises need to be documented therefore sample size (kilometers sampled) needs to be increased. By coupling transects closer together and increasing the length of each transect from 1.6 km to 2.0 km, we will be able to increase the number of kilometers sampled in 2002 without any appreciable increase in cost. Thus, nearly 5500 km of transects are planned to be sampled in 2002, again sampling all DWMAs and Critical Habitat areas rangewide. The above sampling effort would not have been possible without the dedicated cooperation of contractors and volunteers, support of the Desert Managers Group and the Mojave Desert Ecosystem Program, and funding provided by the Bureau of Land Management, National Park Service, Department of Defense, Fish & Wildlife Service, Arizona Game & Fish Department, Utah Division of Wildlife Resources, and the Habitat Conservation Plans of Clark County Nevada and Washington County, Utah.