TRACE ELEMENT AND STABLE ISOTOPE STUDIES OF BLACK BEAR HAIR, BIG BEND NATIONAL PARK AREA, TEXAS AND MEXICO

Black bears in Big Bend National Park (BBNP) were hunted to elimination in the first half of the 20th century but naturally re-colonized BBNP in the late 1980s from mountain habitats in Mexico, southeast of the park. Recent drought has produced difficult conditions and the small (~10-30) bear population in BBNP has fluctuated. Moreover, BBNP encompasses and is adjacent to the Terlingua mercury (Hg) mining district, which was the 3rd largest Hg producer in the U.S., with mining continuing until 1973. Reproductive difficulties in peregrine falcons have been linked to Se and Hg concentrations in insectivorous bird and bat prey species (Mora et al., 2002). The ultimate source of Hg, and possibly Se, is inferred to be mine waste and materials dispersed by wind or water from mine sites into the ecosystem. Bear hair samples have been analyzed for trace element and stable isotope (C, N, and S) contents to determine food sources and potential toxic element consumption. Results indicate that δ¹³C _PDB ,ƒn δ>¹⁵N _AIR , and δ³⁴S_VCDTƒnƒnvalues show distinct ranges from different areas: hair samples from the Chisos Mountains have average values of -16.9°"1.6, 4.5°"1.0 5.2°"0.5 per mil (n=20), respectively, whereas samples from the Serranias del Burro Mountains in adjacent Coahuila, Mexico, average -19.8°"0.7, 4.1°"0.5, 7.3°"0.5 (n=9), respectively. The δ ¹³C values for bear hair from both the Burro and Chisos Mountains suggest that the diet is mainly C4 plants that thrive in desert environments and typically have higher δ¹³C ranges. The higher δ³⁴S values for bear hair samples from the Burros may be due to a significantly different geological setting. Trace element studies of bear hair indicate detectable concentrations as follows, with average and range of concentrations in μg/g for all samples in parentheses: Ba (13.2; 2.4-42.5), Cd (1.20; 0.04-9.90), Cu (15.1; 6.5-49.6), Fe (319; <50-1120), Hg (0.10; <0.02-0.15), Mn (17.4; 1.4-50.9), Mo (0.19; <0.05-0.24), Ni (5.52; 1.4-14.2), Pb (3.07; 0.71-30.2), Se (1.18; <1-1.8), and Zn (129.8; 94.8-151). Except for Hg, few comparative data are available in the literature. Concentrations of Hg are low compared to grizzly bear hair from Yellowstone National Park (Hg=0.02-2.60 μg/g) that feed on spawning cutthroat trout. Therefore, it is unlikely that Hg in BBNP is affecting bear health.