Temperature and Elemental Concentration Effects on Rates of Strontium Incorporation in Walleye Otoliths During Early Life Stages

As they grow, fish otoliths take up trace elements from the ambient water, allowing otoliths to serve as natural tags for identifying natal origins and migratory patterns of individuals. Before using otolith chemical composition as a natural tag, we must first understand how long it takes the elemental concentration in otoliths to reach equilibrium with the ambient environment, which may vary as a function of both water elemental concentration and temperature. This understanding is especially important for species in which larvae do not reside in their natal environments long after hatching, such as river-spawned walleye (Sander vitreus). Toward this end, we conducted a 3 X 2 factorial design experiment wherein walleye were reared from fertilized eggs to 40 days post-hatch in aquaria with water that varied in strontium (300, 900, and 1500 ppm, representing levels of Sr in 3 spawning sites in Lake Erie) and temperature (8 and 13°C). Larvae were sampled at sub-weekly to weekly intervals to allow us to characterize changes in otolith elemental concentration, using laser-ablation inductively coupled plasma-mass spectrometry. Although we have not yet quantified exactly at what point equilibrium with the ambient environment is reached, preliminary results demonstrated that otoliths reflected ambient strontium levels by day 20, with water temperature having little effect on uptake rates.