Strontium signal lag in otoliths of juvenile sockeye salmon (<i> Oncorhynchus nerka</i>) during transition from the freshwater to marine environments

Abstract

The shift in strontium (Sr) concentrations in fish otoliths is a commonly used proxy for identification of marine environment entry during diadromous migrations. However, there is still controversy about the appearance of the Sr-based sea entry mark relative to the true point of entry. In this study, the Sr signal lag was assessed in otoliths of juvenile sockeye salmon (Oncorhynchus nerka) under experimental conditions replicating the transition to seawater during juveniles’ seaward migration. A Sr signal delay was observed to average at 8.2 (SD = 5.1) days for fish with a body length of 140–170 mm (and a weight of 30–70 g). This lag may be species-specific and should be taken into consideration when estimating marine entry timing and marine residence duration of juvenile salmon.