Interior Rolling the Dice on Future of the Desert Tortoise

The U.S. Fish and Wildlife Service's (FWS) biological opinion provides a seemingly conflicted and reluctant expression of support for the Silver State South solar project on the basis of mitigation measures that it admits may not offset the damage done by the project to the viability of a key habitat linkage for the desert tortoise.  The biological opinion is FWS' contribution to the Bureau of Land Management's (BLM) environmental review of the Silver State South project, and evaluates how the project will impact the desert tortoise.   Perhaps to speed approval of the project, the opinion glosses over a significant potential consequence of the project - local extirpation of the desert tortoise population in the Ivanpah Valley.

The Silver State South solar project would be built at the pinch point of the hour-glass shaped Ivanpah Valley, and potentially isolate two populations of the desert tortoise; both the BLM and FWS acknowledge that "current research does not indicate whether reductions in the width or configuration of the corridor compared to existing conditions would reduce or eliminate its ability to maintain the genetic linkage between populations north and south of the Project area." In other words, the Department of Interior plans to approve the Silver State South Solar project even though it does not know if the Silver State South project will essentially sever the habitat linkage.


If the Silver State South project does reduce the viability of the habitat linkage, extirpation of the desert tortoise from the Ivanpah Valley seems to be a possible outcome, although the FWS' biological opinion is written in such a way to avoid direct mention of this outcome.  According to the biological opinion, "[l]oss of population connectivity between the northern and southern portions of Ivanpah Valley would create a nearly closed population of desert tortoises within a 258-square-mile area in its southern portion...and a nearly closed population within the 255-square-mile area of the northern portion of the valley."

The consequences of cutting the habitat linkage are summed up in the biological opinion as "demographic stochasticity and genetic deterioration likely [to] diminish the potential for population growth."  In other words, the project could divide one larger population into two smaller isolated populations that would be too small to maintain population growth in the face of natural and man-made changes (including climate change, wildfire, and natural fluctuations in birth rate, sex ratios, and age distribution), and could cease to exist over time.  As the FWS notes in the revised recovery plan for the desert tortoise that it issued in 2011, such habitat fragmentation places isolated populations "at higher risk of localized extirpation from stochastic events or from inbreeding depression (Boarman et al. 1997; Boarman and Sazaki 2006)."  The Ivanpah population covers a significant portion of the eastern Mojave Desert, and its decline could have ripple effects on the ecosystem.

The biological opinion notes that the northern and southern Ivanpah populations already fall slightly below the recommended density of tortoises necessary to maintain a stable or growing population, suggesting the project's impediment on the habitat linkage could push the populations over the edge.

Ineffective Mitigation

The FWS biological opinion evaluates several mitigation measures that will be funded by First Solar, but the document casts doubt on whether any of them can actually offset the damage that will be done by the solar project to the habitat linkage.  The mitigation measures mostly attempt to reduce tortoise mortality elsewhere in the Ivanpah Valley.  For example, First Solar will pay for tortoise fencing along the Morningstar Mine Road several miles away from the project, and closure of illegal off-highway vehicle (OHV) routes elsewhere in the eastern Mojave recovery unit.  The routes to be closed are unlikely to be the routes in the habitat linkage since the BLM states in the Final EIS that it does not plan to close any routes on the Nevada side of the Ivanpah Valley.

The Final EIS and biological opinion also notes that First Solar's mitigation funds will enable increased law enforcement patrols in the area to "reduce damage to habitat and injury and death of desert tortoises." However, the BLM will continue to manage the Special Recreation Management Area (SRMA) that overlaps the habitat linkage for "intensive recreation," including competitive OHV events that draw thousands of participants.  Given that so many OHV routes will remain open in the SRMA, it's not clear what illegal habitat destruction law enforcement will be able to detect or stop.  OHV events in the habitat linkage will continue to result in desert tortoise mortality, but the impacts will be compounded by the loss of habitat to the Silver State South solar project.

The only serious effort to offset the damage to the habitat linkage may not even be feasible.  FWS states that it may be possible to remove fencing around the Large-Scale Translocation Site - a portion of the desert on the opposite side of Interstate 15 that hosts tortoises translocated from other parts of Clark County, Nevada - to open up a marginal connectivity corridor on the other side of the valley.  Because of the potential that the tortoises there suffer from diseases at a higher rate than the natural population in the Ivanpah Valley, it may not be prudent to remove the fencing.  Even if the fencing is removed, however, FWS notes:
"If the Bureau is able to remove or realign the fence around the Large-Scale Translocation Site, the improved connectivity on the west side of Interstate 15 would not completely compensate for decreased connectivity to the east of the Silver State South Project, primarily because Primm and the Stateline Hills comprise impermeable and semi-permeable barriers, respectively, to movement of desert tortoises through this area."

Kicking the Can Down the Road

So this is where we stand:
  • FWS and BLM are not sure if the Silver State South solar project will diminish the viability of the desert tortoise habitat linkage.
  • If the Silver State South project severs the habitat linkage or renders it ineffective, the result will be two isolated populations of desert tortoise across over 500 square miles that will be too small to maintain population growth over time.  They could disappear altogether in the face of other threats, and without a linkage that enhances the species' resilience.
  • The mitigation measures required by the Final EIS may help reduce overall direct mortality in the region, but it is not clear if this will make a difference after First Solar destroys tortoise habitat in the narrow corridor between Primm and the Lucy Gray mountains.
What is even worse is that we may not know exactly how the project impacts the viability of the habitat linkage for quite some time, given the slow reproductive rate of the desert tortoise.  According to the biological opinion:
"Although the loss of habitat would occur in a relatively short time and be clearly visible, loss or degradation of connectivity would likely not occur for several years and be more difficult to detect."
So what is the Department of Interior's response?  The U.S. Geological Survey will conduct a long-term monitoring effort in an attempt to detect degradation of the habitat linkage's effectiveness.  If the monitoring detects a change, the BLM would have to re-initiate formal consultations under the Endangered Species Act and implement efforts to remediate the damage to the habitat linkage.  However, neither the biological opinion nor the Final EIS identify specific remediation efforts or what positive effect they could have on the viability of the habitat linkage.  Would they decommission the Silver State South solar project early and attempt to restore the habitat?  Would they sponsor speed-dating events for tortoises in the area? Would they blast through the Lucy Gray Mountains to widen the habitat corridor? If these ideas sound ridiculous it's because there is not much you can do to improve connectivity once you have bulldozed 3.7 square miles of tortoise habitat at the narrowest point of a habitat linkage.

The Silver State South Solar project could effectively isolate and decimate two large populations of the desert tortoise, but the BLM plans to approve it anyways with the hope that they can implement unspecified remediation efforts years after the habitat is already destroyed.  Without identifying what those measures are, there is no reason to believe that the damage can be undone.

Rose-Colored Glasses

Even after all of that uncertainty and doubt, the biological opinion concludes "that the proposed actions are not likely to appreciably diminish reproduction, numbers, or distribution of the desert tortoise in the action area, or to appreciably impede long-term recovery of the desert tortoise." FWS is betting on an unknown ability to correct this mistake even after the project is built. 

All of this begs the question: why must First Solar construct this large project at the narrowest part of the Ivanpah Valley habitat linkage?  This destruction is simply not necessary.  First Solar could install these solar panels on already-disturbed lands elsewhere in the southwest without jeopardizing the future of an entire population of the desert tortoise.  In our necessary efforts to cut fossil fuel emissions, there is no need to accept far-reaching and unnecessary compromises of our conservation ethic.

Below is a full copy of the biological opinion for the Silver State South and Stateline solar projects:


  1. I've begun going throught the above FWS document and don't like what I'm reading at all - translocation of Mojave Desert tortoises?

    Ft. Irwin destroyed entire populations of tortoises when they removed them while hibernating.

    Furthermore on pg 2 the assertion is that this project will not encroach on critical habitat (exception) in one area. This is absolutely crazy.

    I did some research on the proposed Hidden Hills project. The area gets a maximum of 4 inches of rain a year. The aquifers have been compromised for other projects, for Pahrump and everything else that can be rationalized by this group of monkeys. Can someone adivse on a course of action besides phone calls to BLM, Dept of the Interior and the "Applicant" please?


Post a Comment

Popular posts from this blog

How Many Plants Species in the Desert?

Mowing Vegetation as Mitigation: Trump Administration Practice Goes Unchallenged

The Absurdity of the Cadiz Water Export Scheme