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29th Annual Meeting and Symposium of the
Desert Tortoise Council, February 20-23, 2004
Abstracts
Effectiveness of Desert Tortoise Recovery Actions: A Review of the Supporting Evidence
William B. Kristan III1 and William I. Boarman2
1Department of Biological Sciences, California State University,
San Marcos, CA 92026
2USGS-Western Ecological Research Center, San Diego, CA
Modern wildlife management strives to base practices on science. However, management actions cannot wait for scientific knowledge to accumulate, and are made with the best available science at the time, which can cause later difficulties when management actions are challenged. We investigated the scientific basis for recovery actions used for desert tortoises, both to determine its coverage (i.e. are there studies that address the effectiveness of recovery actions used today?) and its reliability (i.e. are the studies available scientifically defensible?). We collected peer-reviewed journal articles, unpublished reports, and other forms of information desert tortoise managers use to support their recovery actions, and evaluated topics addressed and major findings. Additionally, we compared each study to general criteria for reliability of scientific studies (e.g. the most reliable studies use experimental manipulation, randomization, replication, and controls whereas deviations from these practices reduce reliability). We found that studies of threats to tortoises are fairly common. However, since reduction in a single known threat for a species limited by multiple threats (such as road mortality and raven predation) may not result in recovery, we considered reduction in threat to be a necessary but not a sufficient demonstration of effectiveness of a recovery action. Studies of effectiveness of recovery actions are rare, and we found no study that experimentally demonstrated a tortoise population recovery following a recovery action. We propose a series of increasingly stringent assumptions that must be made for observations of reduced threats to be considered recovery, so that existing studies can be better placed in a recovery context.
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