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Assessing Trophic Position and Mercury Accumulation in Sanpping Turtles
LAKE, J. L., S. A. RYBA, AND J. R. SERBST. Assessing Trophic Position and Mercury Accumulation in Sanpping Turtles. Presented at The Wildlife Society 16th Annual Meeting, Monterey, CA, September 20 - 26, 2009.
The purpose of this research was to examine the accumulation of mercury in snapping turtles.
This study determined the trophic position and the total mercury concentrations of snapping turtles (Chelydra serpentina) captured from 26 freshwater sites in Rhode Island. Turtles were captured in baited wire cages, and a non-lethal sampling technique was used in which tips of claw nails were cut from turtles (n = 84). Biopsy samples of tail muscle were taken from a subset of turtles (n = 11). Significant predictive relationships (p < 0.05) were found between samples of claw nail and tail muscle tissues for both [Hg] (r2 = 0.70) and δ15N (r2 = 0.68). These relationships were used to estimate site means for [Hg] and δ15N in tail muscle tissue from analysis of claw nail samples. These site mean estimates were compared with those found in muscle tissue of largemouth bass (Micropterus salmoides), at common sites. The site mean [Hg] and δ15N estimated in turtle tail muscle, 529 ± 321 ng Hg /g (wet), and 12.1 ± 2.2 ‰, respectively, were not significantly different than the corresponding site means for muscle tissue of largemouth bass, 552 ± 247 ng Hg /g (wet) and 13.1 ± 2.0‰. In addition, comparisons of values from analysis of claw nails with those from bass muscle showed significant relationships (p<0.05) for both [Hg] (r2 = 0.74) and δ15N (r2 = 0.65). These results show that [Hg] in muscle tissue and the trophic position are similar in snapping turtles and largemouth bass, the top level predatory fish at these sites. These results suggest that these turtles occupy a trophic position at the fourth level (approximately three trophic steps above the primary producers). Sampling and analysis of claw nails from snapping turtles appears to be a useful non-lethal technique for determination of [Hg] concentrations and trophic positions in snapping turtles.