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Federal Register / Vol. 86, No. 157 / Wednesday, August 18, 2021 / Rules and Regulations of a San Marcos salamander was expected if dissolved oxygen dropped below 3.4 mg/L for extended periods i.e., 25 days Woods et al. 2010, pp.
544, 549551.
Lower dissolved oxygen values have been noted at sites inhabited by the Georgetown and Salado salamanders, with measured values as low as 1.5 mg/
L Cambrian Environmental 2018, p.
22. Reported impacts to Georgetown and/or Salado salamanders, in the presence of lower dissolved oxygen, are limited. One Georgetown salamander site i.e., Swinbank Spring experienced a decrease in dissolved oxygen to 2.2
mg/L in June 2016, with levels rebounding in July 2016 to 6.4 mg/l Cambrian Environmental 2017b, p. 8.
No decline in numbers of salamanders was noted after that event Cambrian Environmental 2017b, p. 22. Dissolved oxygen at that spring averaged 7.2 mg/
L for the remainder of 2016 Cambrian Environmental 2017b, p. 8. Conversely, Cobbs Spring, occupied by the Salado salamander, experienced a decrease in dissolved oxygen to 3.2 mg/L in February 2016, and remained below 4.0
mg/L into March 2016 Cambrian Environmental 201a8, p. 13. That low dissolved oxygen event was followed by sharper declines in August 2016 to 1.5
mg/L with dissolved oxygen remaining below 4.0 mg/L through September 2016
Cambrian Environmental 2018a, p. 13.
Numbers of Salado salamanders observed at this spring declined after the latter event and remained low throughout 2017 Cambrian Environmental 2018a, pp. 13, 4243.
Subsequently, numbers of Salado salamanders observed at this spring have increased Cambrian Environmental 2020, p. 18.
Based on available water quality data, the six relatively intact springs in Bell and Williamson counties are generally characterized by average dissolved oxygen of 6.6 mg/L with recorded levels ranging from 1.5 to 13.3 mg/L Diaz et al. 2015, p. 10; Diaz et al. 2016, p. 14;
Cambrian Environmental 2016, pp. 3, 5, 7; Cambrian Environmental 2017a, pp.
3, 5, 7; Cambrian Environmental 2017b, pp. 5, 8, 12; Diaz and Montagne 2017, p. 17; Cambrian Environmental 2018a, pp. 4, 9, 13; Cambrian Environmental 2018c, pp. 1314; Cambrian Environmental 2019a, pp. 3738;
Cambrian Environmental 2019b, pp.
295297, 329; Cambrian Environmental 2020, pp. 3536. Dissolved oxygen below 4.5 mg/L appears to have some impact on Salado salamander abundance. This is consistent with observed effects on the Barton Springs and San Marcos salamanders Turner 2004, pp. 57, 10; Turner 2009, pp. 12

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15; Woods et al. 2010, pp. 544, 549
551. Woods et al. 2010, p. 540 states that an ambient concentration of dissolved oxygen of 5.0 mg/L appears adequate to sustain Eurycea salamanders. Therefore, we presume that dissolved oxygen in the range of 5.0
to 13.0 mg/L is important to the Georgetown and Salado salamanders for respiratory function. Research is needed to better define the physiological tolerances of the Georgetown and Salado salamanders to low dissolved oxygen.
The conductivity of water is also important to salamander physiology.
Increased conductivity is associated with increased water contamination and decreased Eurycea abundance Willson and Dorcas 2003, pp. 766768; Bowles et al. 2006, pp. 117118. The lower limit of observed conductivity in developed Jollyville Plateau salamander sites where salamander densities were lower than undeveloped sites was 800
micro Siemens per centimeter mS/cm Bowles et al. 2006, p. 117.
Salamanders were significantly more abundant at undeveloped sites where water conductivity averaged 600 mS/cm Bowles et al. 2006, p. 117. Because of their similar physiology to the Jollyville Plateau salamander, we presume that the Georgetown and Salado salamanders will have a similar response to elevated water conductance i.e., specific conductance. Water conductance at six relatively intact salamander sites averaged 671 mS/cm and ranged from 317 to 814 mS/cm Diaz et al. 2015, p.
10; Diaz et al. 2016, p. 14; Cambrian Environmental 2016, pp. 3, 5, 7;
Cambrian Environmental 2017a, pp. 3, 5, 7; Cambrian Environmental 2017b, pp. 5, 8, 12; Diaz and Montagne 2017, p. 17; Cambrian Environmental 2018a, pp. 4, 9, 13; Cambrian Environmental 2018c, pp. 1314; Cambrian Environmental 2019a, pp. 3738;
Cambrian Environmental 2019b, pp.
295297, 329; Cambrian Environmental 2020, pp. 3536. Although one laboratory study on the related San Marcos salamander demonstrated that conductivities up to 2,738 mS/cm had no measurable effect on adult activity Woods and Poteet 2006, p. 5, it remains unclear how elevated water conductance might affect juveniles or the long-term health of salamanders in the wild. Bowles et al. 2006, pp. 117
118 documented lower densities of the Jollyville Plateau salamander at sites with higher amounts of human development and high specific conductance i.e., average of 917 mS/
cm. Greater densities of that salamander were observed in
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undeveloped i.e., less than 10 percent impervious cover sites with lower specific conductance 593 mS/cm Bowles et al. 2006, pp. 117118.
Higher specific conductance at developed sites was attributed to the presence of contaminants from roadway runoff, wastewater leakage, and fertilizer use Bowles et al. 2016, pp.
118119. A more recent assessment of contaminants uptake in the Georgetown, Jollyville Plateau, and Salado salamanders found higher amounts of contaminants e.g., organochlorines and polycyclic aromatic hydrocarbons at more heavily developed sites i.e., greater than 10 percent impervious cover and in the tissues of the salamanders themselves Diaz et al.
2020, pp. 291294. In that study, specific conductance of developed sites averaged 798 mS/cm, whereas sites with little to no impervious cover averaged 684 mS/cm Diaz et al. 2020, Table S5.
In the absence of better information on the sensitivity of salamanders to changes in conductivity or other contaminants in the wild, it is reasonable to presume that salamander survival, growth, and reproduction will be most successful when water quality is unaltered from natural aquifer conditions.
Therefore, based on the information above, we identify aquatic invertebrates and water from the Northern Segment of the Edwards Aquifer, including adequate dissolved oxygen concentration of 5.0 to 13.0 mg/L, water conductance of 317 to 814 mS/cm, and water temperature of 61 to 84 F 16 to 29 C, to be physical or biological features essential for the nutritional and physiological requirements of the Georgetown and Salado salamanders.
Cover or Shelter Similar to other Eurycea salamanders in central Texas, Georgetown and Salado salamanders move an unknown depth into the interstitial spaces empty voids between rocks within the substrate, using these spaces for foraging habitat and cover from predators Cole 1995, p. 24; Pierce and Wall 2011, pp.
1617; Jones et al. 2020, pp. 291292.
These spaces should have minimal sediment, as sediment fills interstitial spaces, eliminating resting places and reducing habitat of the prey base small aquatic invertebrates ODonnell et al.
2006, p. 34.
Georgetown and Salado salamanders have been observed under rocks, leaf litter, woody debris, and other cover objects Pierce et al. 2010, p. 295; Diaz and Montagne 2017, p. 10; Diaz and Bronson-Warren, 2019, p. 7.
Georgetown salamanders appear to
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