A method of stock identification based on the elemental composition of striped bass Morone saxatilis (Walbaum) otoliths

Abstract

Fish otoliths usually are formed by daily increment deposits. They are primarily composed of CaCO 3 in the form of aragonite and a protein matrix. Inclusion of elements other than CaCO 3 during increment formation provides the potential to discriminate stocks based on elemental composition. Otoliths of young-of-the-year striped bass Morone saxatilis (Walbaum) from four tributaries of Chesapeake Bay, U.S., were examined using a scanning electron microscope equipped with an energy-dispersive X-ray analyzer. Preparation for X-ray analysis required otoliths be embedded in contaminant-free resin and ground in a frontal plane until the nucleus was reached. A dedicated microprocessor was used to identify elements and to integrate the peak areas. All data were normalized to an integral calcium peak before statistical evaluation. Elements most often included in the otoliths were: Si, Al, Cl, S, Na, K, Mn, Tc, Cr, Cu, Ra, V, and the lanthanide series elements. Stepwise discriminant function analysis demonstrated each riverine group to be distinct, >70% of all individual fish could be correctly assigned to stocks based on the composition of their otoliths. Much improved discrimination resulted from broader geographical groupings.