A federal agency estimates that more than 2,000 desert tortoises may currently occupy the sites of a pair of large planned desert solar projects that would straddle the California/Nevada state line, but says developing the projects won't harm the species.
That's according to the U.S. Fish and Wildlife Service's Biological Opinion, or BiOp, on the proposed Stateline and Silver State South projects, which First Solar wants to build in the Ivanpah Valley near Primm, Nevada.
USFWS estimates that the two projects combined will displace or kill as many as 2,115 desert tortoises, the vast majority of them being small tortoises and eggs that the agency admits may well be destroyed without being detected.
Stateline would occupy more than 2,000 acres on the California side of the line west of Interstate 15, while Silver State South would convert 2,900 acres of desert to solar generating capacity on the other side of the state line and the highway. Silver State South reduced the size of its project plans earlier this year to reduce impacts to the tortoise.
It's no particular surprise that these projects stand to displace thousands of tortoises: the nearby Ivanpah Solar Electric Generating System, now nearing completion immediately to the southwest of the Stateline project, was briefly suspended in 2011 when workers building the plant for BrightSource Energy found hundreds more tortoises than USFWS had expected.
The desert tortoise is protected as Threatened under the Endangered Species Act.
In its BiOp, USFWS finds that Silver State South, which would occupy intact alluvial fan habitat between Ivanpah Dry Lake and the Lucy Gray Mountains, would also create a bottleneck in an important wildlife connectivity corridor for the tortoise. Nonetheless, the agency finds that the two projects are not likely to harm the tortoise's chances for survival as a species.
The BiOp also covers Southern California Edison's proposed construction of an electrical substation in Primm on about 28 acres of land that's expected to house up to 67 tortoises and eggs.
In the BiOp, USFWS distinguishes between "large" tortoises, which are longer than 160 millimeters (about six and one-third inches) on one hand, and smaller tortoises and eggs on the other. Tortoises' growth rate varies, with faster growth following wet winters that provide abundant spring vegetation. But even in a good growth year, tortoises grow slowly, and a 160-millimeter-long tortoise in the Ivanpah Valley might be well into its late teens.
The agency says it expects that the majority of smaller tortoises, and nearly all eggs, will go undetected by the projects' biologists, with the implication being that construction activities will kill many juvenile or infant tortoises without their being detected. As tortoises spend much of their life underground, construction can easily entomb eggs and juvenile tortoises in their dens.
USFWS estimates that the Stateline project houses as many as 94 larger tortoises and 853 smaller tortoises and eggs, while Silver State South is likely to house as many as 115 larger torts and 1053 little ones and eggs.
Under the terms of the Incidental Take Statement included in the BiOp, Stateline must stop work and reconsult with USFWS if they find and relocate more than 89 large tortoises. Silver State South's limit is 107 large tortoises, and the Primm Substation's upper limit is seven.
USFWS declined to set take limits for smaller tortoises and eggs. The agency's rationale for this is that its estimates of the number of smaller tortoises are extrapolated from the its count of larger tortoises; not only are the numbers of smaller torts thus uncertain, but the allowable take of larger animals can serve as a proxy for the smaller ones.
Neither solar project will be allowed to kill more than two tortoises in either relocation efforts or due to roadkill, and that restriction doesn't depend on how big the unfortunate tortoises are. For the Primm Substation, that upper take limit for roadkill or relocation is one each.
The USFWS' observations on likely egg mortality are disheartening. From the Stateline section of the BiOp's Incidental Take Statement:
We expect that most of the eggs present within boundaries of the solar field will be destroyed. We cannot predict how many eggs desert tortoises will produce prior to the onset of construction and the number of eggs present would vary depending upon the time of the year Stateline conducts the clearance surveys. Biologists are unlikely to find many eggs because they are difficult to detect. For these reasons, predicting the number of eggs that may be taken is not possible and we are not establishing a re-initiation criterion for eggs for the loss of eggs.
According to the BiOp, First Solar has agreed to pay for some measures to help mitigate the loss of tortoises and their habitat, including tortoise-proof fencing along two heavily-traveled roads in the area and retiring grazing allotments in the Clark Mountain section of the nearby Mojave National Preserve. Roadkill and habitat displacement from grazing are significant threats to the viability of tortoise populations. The company is also proposing to block and restore illegal off-road routes throughout the tortoises' Eastern Mojave Recovery Unit area, a move USFWS lauds but notes will take a very long time to actually add to usable tortoise habitat.
The BiOp and Incidental Take Statement were released September 30, but were unavailable to the public until late last week due to the shutdown of the federal government.