Development of a species-specific fractionation equation for Arctic charr (Salvelinus alpinus (L.)): an experimental approach

Abstract

A species-specific fractionation equation for Arctic charr (Salvelinus alpinus (L.)) was developed experimentally for use in ecological studies of temperature-driven phenologies for the species. Juvenile Arctic charr were reared in controlled conditions at different temperatures (2-14°C), with three replicates of each temperature. Otoliths from the fish and water samples from the chambers were analysed for oxygen isotope composition and used to estimate temperature-dependent fractionation equations relating the isotopic ratio to rearing temperature. A linear and a second order polynomial relationship were estimated and validated using comparable Arctic charr data from another study. Temperatures predicted using the polynomial equation were not significantly different from recorded experimental temperatures, whereas with the linear equation there were significant differences between the predicted and measured temperatures. The polynomial equation also showed the least bias as measured by mean predictive error. Statistical comparisons of the polynomial fractionation equation to a similarly estimated equation for brook charr (Salvelinus fontinalis (Mitchill)) indicated significant differences. Results imply the need for species-specific fractionation equations, even for closely related fish. Results further suggest the polynomial form of the fractionation equation will facilitate more accurate characterisation of water temperatures suitable for use in ecological studies of temperature-driven phenologies of Arctic charr.

Life history traits of the fish community in Lake Annecy: evidence from the stable isotope composition of otoliths

“…It was found to provide the best fit for both whitefish and pike (Gerdeaux and Dufour, 2012). Equation (1) was published prior to the equations that incorporated appropriate adjustments for the genus Salvelinus and for Arctic char (Godiksen et al, 2010;Storm-Suke et al, 2007). The availability of equations (2) and (3) provides an opportunity to test this assumption for the Lake Annecy Arctic char analysed in the present study.…”

“…(2)), (Storm-Suke et al, 2007) (Eq. (3)), (Godiksen et al, 2010) (3) where α is the fractionation factor between water and otolith aragonite, and T is temperature in Kelvin. The relationship between α and δ 18 O oto is as follows:…”

“…Several studies have suggested that oxygen isotope fractionation between otolith aragonite and ambient water was species-specific and recommended the use of species specific equations (Godiksen et al, 2010). Several authors have noticed significant differences among thermal estimates (Thorrold et al, 1997;Hoie et al, 2004;Storm-Suke et al, 2007).…”

“…Additionally, and perhaps more importantly, the differences in temperature range and experimental design between the different calibration studies could explain the observed variations among studies in the fractionation factors. Otolith treatment method used in some studies (Storm-Suke et al 2007;Godiksen et al, 2010) includes the roasting of samples at high temperature (350 • C). It is well-know that aragonite is metastable and alters to calcite that has its own fractionation factor.…”

Thermal habitat use and juvenile growth of Svalbard Arctic charr: evidence from otolith stable oxygen isotope analyses

“…In lieu of direct observational data, fish otoliths have been used to reconstruct past water temperature Correspondence: Jane A. Godiksen, Norwegian Institute for Nature Research (NINA), Fram Centre, regimes and to make ecological inferences about the fish inhabiting those environments (e.g., the studies by Rowell et al 2005;Godiksen et al 2011). The relationship between water temperatures and otolith oxygen isotope signatures has been quantified using 'fractionation' equations that have been developed for several species (e.g., the studies by Kalish 1991;Høie et al 2004;Storm-Suke et al 2007;Godiksen et al 2010). The relationship between water temperatures and otolith oxygen isotope signatures has been quantified using 'fractionation' equations that have been developed for several species (e.g., the studies by Kalish 1991;Høie et al 2004;Storm-Suke et al 2007;Godiksen et al 2010).…”