Microchemical Analysis of Dorsal Scutes to Infer the Origins and Life Histories of Shortnose Sturgeon

Determining individual origins, movements and life histories within complex population networks is important for understanding how such networks function as a whole.  In the Gulf of Maine, shortnose sturgeon move extensively among multiple river systems, though successful spawning has only been observed in one, the Kennebec River complex. Microchemical analysis of hard structures, usually otoliths, provides a method for inferring life history movements.  We investigated the use of dorsal scutes from shortnose sturgeon as a hard structure that could be used for chronological analysis. Dorsal scutes and pectoral fin spines were collected from wild (n=9) and hatchery-reared (n=15) individuals.  An electron microprobe was used to quantify the ratio of strontium:calcium, a measure commonly used to infer “freshwater” and “seawater” residence. The strontium:calcium ratio in scutes from hatchery fish was stable and relatively low, reflecting stable fresh water conditions.  In contrast, strontium:calcium ratios in scutes and fin spines from wild individuals varied by annuli with the lowest ratios (freshwater) observed in the first and second years.  The strontium:calcium ratio generally increased starting after years two or three (potentially indicating seawater incursion) before declining.  This finding is promising for reconstructing sturgeon life histories and possibly identification of river of natal origin.