OTOLITH ELEMENTAL FINGERPRINTING FOR STOCK IDENTIFICATION OF ATLANTICCOD (GADUS-MORHUA) USING LASER-ABLATION ICPMS

Trace element incorporation into fish otoliths varies among samples co llected at different sites. If otolith elemental composition (the elem ental ''fingerprint'') somehow reflects the characteristics of the amb ient water, the elemental fingerprint of the otolith nucleus could ser ve as a natural marker of fish hatched at different sites. To test thi s hypothesis, Atlantic cod (Gadus morhua) otoliths collected from five spawning grounds in the northwest Atlantic were tested for difference s in elemental and isotopic composition. Laser ablation - inductively coupled plasma mass spectroscopy (LA-ICPMS) was used to assay the conc entration of 14 isotopes (nine elements) in otolith nuclei. The sensit ivity of the laser ablation system exceeded that of the electron micro probe by 2-4 orders of magnitude, with an average CV of 21% for any gi ven isotope. Most isotopic concentrations were consistent between left and right otoliths of a given fish, and most differed significantly a mong sample sites; there were no significant differences by age, sex, or fish length. Multivariate analyses of the elemental fingerprints re sulted in significant discrimination among sample sites. While the mec hanism underlying trace element incorporation into otoliths is still u nclear, otolith elemental fingerprinting has the potential to become a n effective and accurate means of stock identification.