The effect of ablation pattern on LA-ICPMS analysis of otolith element composition in hake, Merluccius merluccius

Laser ablation ICPMS (inductively coupled plasma mass spectrometry) analysis is a powerful tool for studies of fish ecology, based on measurement of the chemical composition of otoliths (ear stones). A key trade-off for this analysis is selecting the size of the ablation area to maximize the resolution for discrete temporal intervals during the life of an individual fish, vs the amount of otolith material required to produce reliable data. Three different widths of ablation lines were used to analyze the otoliths of European hake (Merluccius merluccius). The best temporal resolution was produced by ablation lines of 10 μm width, corresponding to less than 2 weeks in the fish’s life, but the data from this configuration were variable and often below the detection limit for many elements. Ablation lines of 20 and 30 μm width produced accurate and precise data corresponding to approximately 20 and 30 days in terms of temporal resolution. When tested on hake otoliths, the measured element concentrations differed significantly between the 20 and 30 μm lines. The 30 μm ablation line resulted in a better multivariate model for discrimination between populations, with higher classification success and higher probability of individual assignment to source location.