Assessing anadromy of brook char (Salvelinus fontinalis) using scale microchemistry

Abstract

Brook char (Salvelinus fontinalis) exist in both freshwater and anadromous forms, often in sympatry, the ecology of the latter being poorly understood. As strontium (Sr) can substitute to calcium (Ca) and as its concentration in seawater is higher than in freshwater, scale circulii laid down during seawater exposure should be enriched in Sr, allowing precise identification of residence patterns in freshwater and seawater. We attempted to document movements of anadromous brook char using wavelength-dispersive X-ray electron microscopy on individual circulii of sagittally sectioned scales. Body scales of brook char experimentally transferred between freshwater and seawater had elevated Sr/Ca ratios in regions laid down during exposure to seawater. Wild anadromous brook char body scales had consistently higher Sr/Ca ratios than river-resident form. However, in both experimental and wild brook char, Sr/Ca ratios in the scale circulii from freshwater periods showed elevated Sr/Ca ratios after seawater exposure, suggesting whole-scale Sr enrichment associated with exposure to seawater. Although whole-scale elemental composition revealed whether a fish has ever resided in a marine environment, analysis of Sr patterns at the level of individual circulii did not allow resolution of fine-scale patterns of these movements in brook char.