Comparison of secondary ion mass spectrometry and micromilling/continuous flow isotope ratio mass spectrometry techniques used to acquire intra-otolith delta 18O values of wild Atlantic salmon (Salmo salar)

• Published in: Rapid communications in mass spectrometry Vol. 24; no. 17; pp. 2491 - 2498
• Main Authors: Hanson, N N, Wurster, C M, Todd, C D
• Format: Journal Article
• Language: English
• Published: 15.09.2010
• Subjects: Marine; Salmo salar
• ISSN: 1097-0231
• DOI: 10.1002/rcm.4646

The chemical signals in the sequential layers of fish otoliths have the potential to provide fisheries biologists with temporal and spatial details of migration which are difficult to obtain without expensive tracking methods. Signal resolution depends, however, on the extraction technique used. We compared the use of mechanical micromilling and continuous flow isotope ratio mass spectrometry (CF-IRMS) methods with secondary ion mass spectrometry (SIMS) to obtain delta 18O profiles from otoliths of wild Atlantic salmon (Salmo salar) and used these to corroborate the time of freshwater emigration of the juvenile with macroscopic patterns within the otolith. Both techniques showed the transition occurring at the same visible feature on the otolith, allowing future analyses to easily identify the juvenile (freshwater) versus adult (marine) life-stages. However, SIMS showed a rapid and abrupt transition whereas micromilling provided a less distinct signal. The number of samples that could be obtained per unit area sampled using SIMS was 2 to 3 times greater than that when using micromilling/CF-IRMS although the delta 18O values and analytical precisions ( similar to 0.2ppt) of the two methods were comparable. In addition, SIMS delta 18O results were used to compare otolith aragonite values with predicted values calculated using various isotope fractionation equations.