**The title, authors, and abstract for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**
Development of a stable isotope marking technique for early life stages of lake sturgeon
Gregory W. Whitledge1 and Kurt T. Smith1
1Fisheries and Illinois Aquaculture Center, Southern Illinois University, Carbondale, IL 62901-6511 USA
Lake sturgeon, like many other North American sturgeon species, is listed as endangered, threatened, or as a species of conservation concern by several management agencies. Assessments of habitat use and dispersal for early life stages, evaluation of the most suitable life stages for stocking, and methods for differentiating stocked from wild fish are important research needs to support rehabilitation of populations of lake sturgeon and other imperiled species. Tracking fish dispersal and evaluating stocking success require appropriate tagging methods, but conventional tagging methods are limited in their applicability to early life stages or do not provide the possibility for multiple differentiating marks. A recently developed technique for mass marking fish otoliths using stable isotopes offers the potential to produce multiple chemical marks that are distinct from one another and from stable isotope ratios of wild fish. However, examination of otoliths for chemical marks requires sacrificing fish. Naturally occurring trace element signatures in pectoral fin rays have recently been demonstrated to provide valuable new insights into environmental history of fishes, including sturgeons. However, whether techniques developed for marking otoliths with unique stable isotope ratios are also applicable to marking pectoral fin rays has not been evaluated. The objectives of this study were to develop a technique for marking age-0 lake sturgeon pectoral fin rays with stable strontium isotope ratios (88Sr/86Sr) and to evaluate retention of stable isotopic marks. Groups of lake sturgeon were reared in water spiked with different concentrations of 86SrCO3 (0, 25, 50, or 100 μg/L) for 10-24 d. Following the labeling period, fish from each treatment group were retained for up to 120 d to assess mark retention. Stable isotope labeling produced 88Sr/86Sr marks in pectoral fin rays that were distinct from fin ray 88Sr/86Sr of control fish reared in ambient laboratory water, with the 100 μg/L 86SrCO3 treatments consistently yielding the highest rate of marking success. Stable isotopic marks applied to fin rays were retained for 120 d post-labeling and may persist longer. Production of multiple unique batch marks in fin rays of early life stages of fish using stable isotopes will enable researchers to distinguish among different groups of stocked fish from a single source and between stocked and wild fish without having to sacrifice fish to check for marks. The ability to differentiate multiple groups of stocked fish from a single source will facilitate evaluation of factors affecting stocking success, such as stocking location and timing and fish size, as well as assessment of dispersal, habitat use, and survival of marked and released fish when fish may become interspersed following stocking.