An evaluation of electron-probe microanalysis of otoliths for stock delineation and identification of nursery areas in a southern temperate groundfish, Nemadactylus macropterus (Cheilodactylidae)

The chemistry of calcified tissues has been suggested as a source of useful information on the population structure and environmental histories of fishes. We evaluated this possibility by examining in detail regional and ontogenetic variability in the chemical composition of sagittae of juveniles and adults of the temperate marine groundfish Nemadactylus macropterus. Six elements (in order of decreasing abundance, Ca, Na, Sr, K, S, and Cl) were consistently detected in the sagittae at concentrations greater than 200 ppm; all exhibited levels of individual, ontogenetic, and regional variability well in excess of their respective scales of measurement error. Comparisons of juveniles and adults from different sites indicate that composition of the otolith is most alike in fish from adjacent sites, that most juveniles are similar to adults collected from the same site, and that the differences in composition that characterize sites are manifest during most, if not all, of the fish's ontogeny. These results are consistent with the hypotheses that otolith composition reflects population structure and that these populations are largely self-recruiting. However, the results also suggest that the chemical composition of otoliths is much less sensitive to environmental conditions than previously thought. Rather, it appears that regional differences in composition either have a genetic basis or are set by environmental influences early in life and are then maintained throughout subsequent life history.