Inter-laboratory comparison of Atlantic and Mediterranean bluefin tuna otolith microconstituents

Abstract

Elemental analysis of juvenile (age 0+ and 1 year) Atlantic bluefin tuna Thunnus thynnus otoliths by isotope dilution and conventional inductively coupled plasma mass spectrometry (ID ICP-MS and ICP-MS) indicated that the concentrations of certain elements varied among putative nursery grounds in the Atlantic Ocean. Further, trace element fingerprints of age-1 tuna from each nursery–the western Atlantic and Mediterranean Sea–were distinct and varied sufficiently to distinguish individuals from different regions with moderate confidence. Overall correct classification rates for a simulated test set of age-1 tuna were 68% (using ICP-MS) and 81% (using ID ICP-MS), despite a small sample size (9 Mediterranean vs. 19 western Atlantic tunas). Although ID ICP-MS was the more accurate of the two ICP-MS technologies, inter-laboratory precision was moderately high (3–18%) for individual elemental concentrations (Li, Na, Mg, K, Ca, Mn, Sr, and Ba), and multi-variate elemental fingerprints were similarly ordinated between laboratories (r=0.75). Age-0 tuna samples were too small to permit statistical classification tests, but showed similar levels of elemental concentrations between laboratories. Our results indicate that it should be possible to assign nursery ground origin to adult bluefin tuna based on the elemental composition of their extracted otolith core.