DeVries, R.J., and H.L. Schramm, Jr. 2015. Similarities and differences in 13C and 15N stable isotope ratios in two non-lethal tissue types from shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820). Journal of Applied Ichthyology 31:474-478.
Stable isotope analysis has become a useful and reliable tool for assessing long-term feeding patterns and trophic interactions. Recent studies determined δ13C and δ15N signatures derived from fin clips closely approximated signatures derived from muscle tissue, indicating that fin clips were a viable option for non-lethal sampling when the organism is large enough to obtain sufficient fin tissue without impairing the organism. The objective for this study was to compare the δ13C and δ15N signatures of fin tissue and the pectoral spine; both tissues can be obtained non-lethally, and the latter is also used for aging individuals. Thirty-two shovelnose sturgeon Scaphirhynchus platorynchus (fork length [FL] = 500-724 mm) were sampled from the lower Mississippi River. Tissue types differed significantly for both δ13C (P<0.01; spine: mean = -23.83, SD = 0.62; fin clip: mean = -25.74, SD = 0.97) and δ15N (P=0.01; spine: mean = 17.01, SD = 0.51; fin clip: mean = 17.19, SD = 0.62). Neither FL nor FL-tissue type interaction had significant (P>0.05) effects on δ13C. Fin clip δ13C values were highly variable and poorly correlated (r = 0.16, P = 0.40) to those from pectoral spines. We found a significant FL-tissue type for δ15N, reflecting increasing δ15N with FL for spines and decreasing δ15N with FL for fin clips. These results indicate that spines are not a substitute for fin clip tissue for measuring δ13C and δ15N for shovelnose sturgeon, but the two tissues may provide complementary information for assessing trophic position at different time scales.