Trace metals in four structures of fi sh and their use for estimates of stock structure

Studies of the population dynamics of marine fi shes depend on the ability to distinguish separate “stocks” that may make up the total population of a single fi sh species. Although much of fi sheries management assumes that a single population is being monitored, measures of growth, natural mortality, recruitment, and reproduction are often made for the total population because data on movement or stock separation or fi delity (or the combination of all three) are inadequate to allow separation of stocks. A variety of methods exist for identifying stocks (e.g. population parameters, capture-mark-recapture studies, physiological and behavioral characters, morphometric and meristic characters, calcareous characters, cytogenic characters, and biochemical characters; Ihssen et al., 1981), but few methods can provide a reliable measure of stock identity. Genetic techniques are frequently used but fail to differentiate stocks because a small amount of larval or adult mixing among populations makes differences undetectable (Hartl and Clark, 1989). Recently, many studies have focused on the use of “elemental fi ngerprints” (sensu Campana et al., 1994), or the elemental composition of the otoliths, as a measure of stock identity. Initial microchemistry studies tended to focus on diadromous species and distinguished between freshwater and marine life history phases of fi sh (e.g. Bagenal et al., 1973; Belanger et al., 1987; Kalish, 1990; Coutant and Chen, 1993; Rieman et al., 1994). The electron microprobe was widely used for such studies but because of the “typical” concentrations of Ca, Na, Sr, K, S, and Cl found in otoliths, electron probes Trace metals in four structures of fi sh and their use for estimates of stock structure