A field-derived oxygen isotope fractionation equation for Salvelinus species

Field-collected otolith samples of young-of the-year Arctic charr (Salvelinus alpinus) and brook charr (Salvelinus fontinalis) and monitored water temperatures were used to estimate a delta(18)O fractionation equation for the genus Salvelinus. When compared to literature reported equations, the developed fractionation equation had a statistically similar slope but dissimilar intercept. Statistical similarities among fractionation equation slope estimates suggest a common otolith delta(18)O incorporation response among fish species that may be interpreted as widespread equilibrium otolith delta(18)O deposition. Statistical dissimilarities among intercept estimates question broad applicability of any single fractionation equation to all fish species and were interpreted here to have biological meaning as a result of known differences in standard metabolic rates among species. Attempts to statistically cross-validate fractionation equations by prediction of water temperatures used in other fractionation studies indicated significant biases in the range of -7.9 to 6.7 degrees C that preclude the broad use of any single fractionation equation for accurate thermal reconstructions. Differences in equation intercepts and the prevalence of predictive biases do not support the conclusion of previous studies concerning the wide applicability and/or general accuracy of fractionation equations and suggest fractionation equations are best developed at the species- or taxon-specific (e.g., genus) level.