Using Trace Elements in Pectoral Fin Rays to Assess Life History Movements in Sturgeon: Estimating Age at Initial Seawater Entry in Klamath River Green Sturgeon

To investigate the timing of the initial entry of green sturgeon Acipenser medirostris into seawater, we examined the ratios of strontium and barium to calcium in pectoral fin rays via laser ablation-inductively coupled plasma-mass spectrometry. In a reference group of six hatchery fish that was reared 1-2 years in freshwater and 1-3 years in seawater, we found a significant increase in the Sr:Ca ratio. a decrease in the Ba:Ca ratio, and an increase in the Sr:Ba ratio in calcified growth zones during the transition from freshwater to seawater. In 10 wild adults captured in the Klamath River, California, combined evaluation of the Sr:Ca and Ba:Ca ratios provided a clearer understanding of fish movements than the Sr:Ba ratio, probably because wild fish have a more complex life history. The Ba:Ca ratio dropped significantly between growth zones 1 and 2 (ages 0.5-1.5), indicating a transition into saline waters, such as the Klamath River estuary. The Sr:Ca ratio increased slightly in the same location but attained the values found in reference fish held in seawater between growth zones 3 and 4 (ages 2.5-3.5). The Sr:Ca, Ba:Ca, and Sr:Ba ratios in growth zones 46 (ages 4.5-6.5) of wild fish were similar to those found in reference fish held in seawater and corroborated the results of previous physiological studies as well as the limited field data. These results demonstrate the usefulness of trace element analyses of green sturgeon pectoral fin rays and confirm an early age of entry into seawater for this species.