Is otolith strontium a useful scalar of life cycles in estuarine ®shes?

The ef®ciency with which estuarine habitats produce ®sh is poorly understood due to the complexity of life cycles. Spatial dynamics of estuarine ®shes comprise retentive and dispersive behaviors which occur on seasonal and ontogenetic scales. Salinity is an important scalar in the spatial dynamics of estuarine ®shes, that may affect production and dispersal. In this paper, we review investigations that used otolith strontium (Sr) to chart estuarine movements of ®shes. Based upon microprobe analysis of otolith Sr, variable patterns of estuarine ingress have been shown for bay anchovy Anchoa mitchilli, freshwater eel Anguilla spp., Japanese sea bass Lateolabrax japonicus, and Atlantic croaker Micropogonias undulatus. In anadromous ®shes, striped bass Morone saxatilis American shad Alosa sapidissima, and Arctic charr Salvelinus alpinus, otolith Sr has been used to record emigration of juveniles and adults from freshwater and oligohaline nurseries. These same species showed seasonal cycles in otolith Sr consistent with expectations on frequency of spawning migration. A critical yet seldom evaluated issue is the relative roles of salinity, temperature, ontogenetic stage, and physiological state on otolith Sr. In a review of the literature (1982±1997), we found that these effects were infrequently evaluated (10 of 27 species investigated). Rarer still were studies of the interaction of these effects on otolith Sr. Only a single study had calibrated a laboratory-based salinity vs. otolith Sr relationship using ®eld data. Based upon values obtained through the literature review, we observed a positive relationship between otolith Sr and habitat salinities among freshwater, estuarine, and marine taxa. # 2000 Elsevier Science B.V. All rights reserved.