Scaphirhynchid Sturgeon Early-Life History

Rehabilitation of sturgeon populations requires an understanding of the autecology during all life stages, especially during early life when high mortality occurs.  To begin to understand sturgeon early-life history we determined river of origin, habitat use, and early-life dynamics in an unimpounded reach of the Mississippi River. Our trace element analyses suggest that age-0 sturgeon captured in the middle Mississippi River have drifted from as far upstream as the Gavins Point Dam on the Missouri River (> 1200 Km), while other individuals originated locally in the Middle Mississippi River.  On a more refined scale of specific habitats used (post-drift), age-0 Scaphirhynchus sturgeon catch rates were highest around artificial structures (i.e., wing dikes) and island areas while main channel habitat comprised the lowest catch rates. Within these habitats, young sturgeon frequently occupied low velocities (i.e., ~0.1 ), moderate depths (i.e., 2 to 5 m), and sand substrate. Although determination of river of origin and specific habitats used are imperative for restoration they likely regulate early-life dynamics. Mean sturgeon growth rates ranged from 1.42-1.50 mm/d over the four years; however, growth rates did not differ among years. Individuals hatched over a 25 to 50-d period and peak hatch dates were between 10- 20 May in all years.  Moreover, hatch timing coincided with optimum spawning temperatures of 17-20 ^oC and an increase in river stage.  Abundance appeared to be regulated by river stage; longer durations of high water related to higher relative abundance.  Mortality increased with the number of days where water temperature exceeded 28 ^oC.  In the end this study has laid the framework for understanding early-life ecology of Scaphirhynchus sturgeon.  Furthermore, we believe that this research will be used to begin to rehabilitate these imperiled sturgeon populations.