Chemical signatures of otoliths and application in fisheries

The very successful 141 American Fisheries Society Annual Meeting was held in Seattle from September 4–8, 2011. During the meeting we organized an otolith symposium titled “Chemical signatures of otoliths and application in fisheries”. Twelve oral and three poster presenters from China, Japan, Norway, and United States were presented in the session, and contributed as manuscripts for publication in a special issue of Environmental Biology of Fishes. Why do we think this is important? First, the chemical signatures of otoliths have received increased attention in recent years because otoliths contain a great deal of information about the life history of the fish and that information can be extracted from stable isotope and trace elemental analyses. Second, although otolith chemistry has been investigated since the 1960s (e.g., Lowenstam 1961; McIntire 1963; Devereux 1967; Degens et al. 1969), very few symposia have concentrated specifically on the topic. Therefore, we think it is important and timely to highlight our AFS otolith symposium and publish the presentations. Otoliths are mm-sized, laminated calcium carbonate structures (CaCO3) found in the inner ears of teleost fish (Carlstrom 1963). They grow from a fluid medium (endolymph) that mainly contains calcium ions Ca and bicarbonate HCO3 (Schwarcz et al. 1998). From the mineralogical perspective, carbonates consist of 3 minerals: rhombohedral calcite and dolomite, and orthorhombic aragonite. Aragonite is unstable in nature and commonly inverts to its polymorph calcite (Nesse 1986). During the precipitation and physicochemical processes minor or trace elements are incorporated into carbonate mineral phases by substituting for Ca in the crystal structure. The divalent metal cation M in the calcite group occupies the octahedral sites with 6-fold coordination, whereas M in the aragonite group occupies the triangular sites with 9-fold coordination (Berry et al. 1983; Zheng 1999). Thus trace elements with larger ionic radii, such as Sr, Na, and Ba, are preferentially incorporated into orthorhombic aragonite, whereas rhombohedral calcite is enriched in smaller ions, such as Mg, Fe, Mn, Zn, and Cd. At normal or low temperature conditions this substitution is governed by a distribution coefficient (df) of a special trace element between liquid and solid phase that can be expressed by: