Sunday, January 16, 2011

Desert Tortoise Monitoring Report Available

The Desert Tortoise Recovery Office released the draft Range-wide Monitoring of the Mojave Population of Desert Tortoise: 2010 Annual Report.   The surveys of key desert tortoise habitat revealed higher densities of tortoise in some areas than were observed in previous years, although the report judges that for 3 of the monitored areas, the densities are consistently high.  However, because of refinements in the survey techniques and resources available for the surveys, accurate population trends cannot be established from the surveys yet.

According to the draft report, tortoise density in the Ord-Rodman critical habitat unit was 7.5 animals per square kilometer.  The surveys in 2008 and 2009 noted a density of 6 per square kilometer.   Surveys in the Ivanpah critical habitat unit observed only 5 tortoises, resulting in an estimated density of 1.1 tortoise per square kilometer.  This is significant because construction crews for the nearby Ivanpah Solar Energy Generating System--being built by BrightSource Energy--have already displaced at least 50 tortoises in the initial phase of the project.  The tortoise density at the BrightSource site is a testament to the relative health of the Ivanpah Valley ecosystem, which could be crucial to the future recovery of the desert tortoise if it is not destroyed for the sake of energy development.

Desert Tortoise on the site of the proposed Calico Solar power project.  Photo from BLM Environmental Impact Statement.
A separate document released in September 2010, the "Status of the Species and Critical Habitat Range-wide" details key principles that should be adhered to in order to enhance the prospects of the desert tortoise's recovery.  Among the principles, the report encourages the conservation of large blocks of habitat, avoidance of habitat fragmentation,  distribution of conservation areas across the species' range, and low edge-to-area ratio for protected land, which is intended to avoid urbanization and industrialization along the edge of preserved habitat from impacting the interior.

The report notes that the tortoise faces increased threats from development, invasive plant species that are less nutritious and encourage wildfire, human activity that has increased the raven population (which have been known to hunt tortoises), and continued problems with an upper-respiratory tract disease.  The report judges that the desert tortoise currently faces a "low potential for recovery, adjusted based on current uncertainties about various threats and our ability to manage them."

A map from the Desert Tortoise Recovery Office depicting critical habitat units where the populations were surveyed.

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