Validation of dried blood spot sampling for determining trophic positions of Arctic char using nitrogen stable isotope analyses of amino acids

Rationale Dried blood spots (DBSs) are gaining popularity for biomarker analyses in ecological research due to their advantages for use in field‐based research and in remote settings; however, many DBS biomarkers remain unvalidated. We validated the application of compound‐specific stable nitrogen isotope analyses of amino acids (CSIA‐AAs) to field‐prepared DBSs for determining trophic positions of wild‐caught Arctic char (Salvelinus alpinus). Methods Whole blood and muscle from Arctic char were collected, and DBSs were created in the field. We measured the stable nitrogen isotope ratios (expressed as δ15N values) of the amino acids glutamic acid (Glu) and phenylalanine (Phe) isolated from Arctic char samples using CSIA‐AAs. We then compared amino acid δ15N values from DBSs and the other sample types (whole blood and muscle) from the same specimens. We calculated and compared trophic position estimates generated from whole blood, DBSs, and muscle. Results The δ15N values of Glu and Phe, as well as trophic position estimates from DBSs, were highly correlated with δ15N values and estimates from both whole blood and muscle. The DBS amino acid δ15N values and trophic position estimates agreed well with those from whole blood. Although mean differences between amino acid δ15N values from DBSs and muscle were noted, the offsets were small and resulted in a 0.2 mean difference between trophic position estimates for DBSs and muscle. Conclusions We demonstrate that the application of CSIA‐AAs to field‐prepared DBSs of Arctic char generates similar trophic position estimates to those from whole blood and muscle. We suggest that DBSs could be developed as a minimally invasive sampling technique to study feeding ecology of wild fish and perhaps other organisms of interest.