CAN OTOLITH MICROCHEMISTRY CHART PATTERNS OF MIGRATION AND HABITAT UTILIZATION IN ANADROMOUS FISHES

Seasonal and ontogenetic patterns in estuarine and coastal migrations of anadromous fish species have important consequences to their survival, growth, recruitment, and reproduction, We tested the hypothesis that otolith (sagitta) microchemistry can document the environmental history of individual fish across an estuarine salinity gradient. Juvenile striped bass, Morone saxatilis (Walbaum), (80 days posthatch) were reared for 3 wk in aquaria at two temperatures and six salinities. The ratio of strontium/calcium (Sr/Ca) deposited in the sagittal otoliths of reared juveniles was positively related to salinity, Temperature and growth rate had relatively minor, but significant effects on the Sr/Ca ratio. In a second experiment, juveniles (80 days posthatch) were exposed to increasing salinity (0 ppt to 25 ppt) and then decreasing salinity (25 ppt to 0 ppt) over a 20-wk period. Electron microprobe examination of the otoliths from these juveniles showed a gradual rise and decline in Sr/Ca during the experimental period which corresponded directly with experimental changes in salinity. Field data on subadult and adult striped bass corroborated the laboratory analyses and indicated a logistic relationship between ambient salinity and otolith Sr/Ca ratio. Verification studies support the use of otolith microchemistry to measure migratory schedules and habitat utilization patterns in anadromous striped bass populations.