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Federal Register / Vol. 86, No. 157 / Wednesday, August 18, 2021 / Rules and Regulations
by a knowledgeable scientist and cited within published articles, unpublished reports, and Service files including Hunter and Russell 1993, p. 78, Pierce and Wall 2011, pp. 23, Chippindale et al. 2000, pp. 3943, Diaz and Montagne 2017, p. 6, Cambrian Environmental 201bc, pp. 5
6, Devitt et al. 2019a, pp. 2,626, 2,628, and Devitt et al. 2019b, pp. 1618. It is very difficult to determine whether a salamander population has been extirpated from a spring site due to these species ability to occupy the inaccessible subsurface habitat. The Georgetown and Salado salamanders are not capable of long-distance dispersal between isolated springs due to their reliance on discrete, groundwaterdependent ecosystems. Springs in central Texas are frequently historical features of the landscape that predate European settlement of the North American continent Brune 1981, pp.
6569, 473476. We, therefore, consider sites with observations of salamanders at the time of listing to be currently occupied, unless that spring or cave site had been destroyed.
Based on our review, the critical habitat areas described below are within the geographical range occupied by at least one of the two salamander species and meet the definition of critical habitat. The true extent to which the subterranean populations of these species exist below ground away from outlets of the spring system is unknown because the hydrology of central Texas is very complex and information on the hydrology of specific spring sites is largely unknown. We will continue to seek information to increase our understanding of spring hydrology and salamander underground distribution to inform conservation efforts for these species. At the time of this final critical habitat rule, the best scientific evidence available indicates that a population of groundwater-dependent Eurycea salamanders can extend at least 984 ft 300 m from the spring opening through underground conduits or voids between rocks. For example, the Austin blind salamander is thought to occur underground throughout the entire Barton Springs complex Dries 2011, pers. comm.. The spring habitats used by salamanders of the Barton Springs complex are not connected on the surface, so the Austin blind salamander population extends at least 984 ft 300
m underground, as this is the approximate distance between the farthest two outlets within the Barton Springs complex known to be occupied by the species.
We designate critical habitat in areas that we have determined are occupied
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by one of the two salamanders and contain physical or biological features essential to the conservation of the species. We delineated both surface and subsurface critical habitat components.
As previously stated, a Jollyville Plateau salamander was observed to have traveled up to 1,640 ft 500 m after multiple years i.e., 20102014 in Bull Creek Bendik et al. 2016, p. 9.
However, the surface critical habitat component was delineated by starting with the spring point locations that are occupied by the salamanders and extending a line upstream and downstream 262 ft 80 m. This was the farthest distance a Eurycea salamander has been observed from a spring outlet over a 4-month period i.e., January to April in a single year Bendik et al.
2016, pp. 910 and is likely a more reasonable distance for salamanders in common hydrological settings. We applied this maximum distance to account for the potential movement and surface habitat use of Georgetown and Salado salamanders upstream and downstream of spring openings. It is reasonable to consider the downstream and upstream habitat occupied based on the dispersal capabilities observed in individuals of very similar species.
When determining surface critical habitat boundaries, we were not able to delineate specific stream segments on the map due to the small size of the streams. Therefore, we drew a circle with a 262-ft 80-m radius representing the extent the surface population of the site is estimated to exist upstream and downstream. This circle does not include upland habitat adjacent to streams. The surface critical habitat includes the spring outlets and outflow up to the ordinary high water mark the average amount of water present in nonflood conditions, as defined in 33
CFR 328.3e and 262 ft 80 m of upstream and downstream habitat to the extent that this habitat is ever present, including the dry stream channel during periods of no surface flow. We acknowledge that some spring sites occupied by one of the two salamanders are the start of the watercourse, and upstream habitat does not exist for these sites. The surface habitat we are designating as critical habitat does not include human-made structures such as buildings, aqueducts, runways, roads, and other paved areas within this circle, nor does it include upland habitat adjacent to streams.
We delineated the subsurface critical habitat unit boundaries by starting with the cave or spring point locations that are occupied by the salamanders. Depth to subsurface habitat will vary from site
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to site based on local geology. From these cave or spring points, we delineated an area with a 984-ft 300-m radius to create the polygons that capture the extent to which we estimate the salamander populations exist through underground habitat. This radial distance comes from observations of the Austin blind salamander, which is thought to occur underground throughout the entire Barton Springs complex Dries 2011, COA, pers.
comm.. The Austin blind salamander is a reasonable surrogate for Salado and Georgetown salamanders, as it also inhabits subsurface, water-filled voids in the underlying Edwards Aquifer Hillis et al. 2001, p. 23. The spring outlets used by salamanders of the Barton Springs complex are not connected on the surface, so the Austin blind salamander population extends a horizontal distance of at least 984 ft 300
m underground, as this is the approximate distance between the farthest two outlets within the Barton Springs complex known to be occupied by the species. This distance was applied to the Georgetown and Salado salamanders given their reliance on subsurface aquifer habitats Bendik and Gluesenkamp 2012, pp. 45; Bendik et al. 2013, pp. 1012, 15; Bendik 2017, p.
5,013; Diaz and Bronson-Warren 2018, p. 11; Devitt et al. 2019, p. 2,625.
Polygons that were within 98 ft 30 m of each other were merged together as these areas have the potential to be connected underground Devitt et al.
2019a, pp. 2,6292,630. Each merged polygon was then revised by removing extraneous divots or protrusions that resulted from the merge process.
Developed areas of surface habitat, such as lands covered by buildings, pavement, and other structures, lack physical or biological features for the Georgetown and Salado salamanders.
The scale of the maps we prepared under the parameters for publication within the Code of Federal Regulations may not reflect the exclusion of such developed lands. Any such lands inadvertently left inside critical habitat boundaries shown on the maps of this final rule have been excluded by text in the final rule and are not designated as critical habitat. Therefore, a Federal action involving these lands would not trigger section 7 consultation with respect to critical habitat and the requirement of no adverse modification unless the specific action would affect the physical or biological features in the adjacent critical habitat.
We designate as critical habitat lands that we have determined are occupied at the time of listing i.e., currently occupied and that contain one or more
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