Water Temperature and River Stage Influence Mortality and Abundance of Naturally Occurring Mississippi River Scaphirhynchus Sturgeon

Several studies have investigated the demographics of shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus in the Mississippi River through assessment of adult populations; however, comparatively few studies have examined the early life history of these species. Here, we describe a comprehensive 4-year study that examined the effects of water temperature and river stage on the mortality, abundance, hatch timing, and growth rates of age-0 Scaphirhynchus spp. sturgeon in the middle Mississippi River. We trawled island areas every 7-10 d from April to August 2004-2007. We captured 1,256 individuals ranging from 10 to 193 mm total length over the 4-year study. Mean age-0 sturgeon growth rates ranged from 1.42 to 1.50 mm/d over the 4 years; however, growth rates did not differ among years. Individuals hatched over a 25-65-d period, and peak hatch dates were between 10 and 20 May in all years. Moreover, hatch timing possibly coincided with optimum spawning temperatures of 17-20 degrees C and an increase in river stage. Abundance appeared to be regulated by river stage; longer durations of high water were related to higher relative abundance. Furthermore, mortality increased with the number of days on which water temperature exceeded 28 degrees C. Based on these data, management strategies may need to ensure sturgeon hatching success and subsequent survival through optimizing hydrologic and thermal regimes that occur during the early life stage.