The effects of substrate and sediment burial on survival of developing pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (S. platorynchus) embryos

The shovelnose sturgeon (Scaphirhynchus platorynchus) and endangered pallid sturgeon (S. albus) deposit demersal and adhesive eggs in swift currents, near or over coarse substrate. Hydrographic surveys have demonstrated the dynamic nature of spawning habitats and that coarse substrates may episodically be buried (partially or completely) by fine sediments. To evaluate embryo survival of both species in various substrate conditions, laboratory trials were conducted with substrates of clean glass, gravel, medium-coarse sand (MCS), and fine sand-silt (FSS). Embryos in MCS and FSS were tested three ways: unburied, partially buried, and fully buried (1–2-mm depth). Embryos were exposed to trial conditions for 10 days from the day of fertilization (5 days beyond expected hatching). For both species, mean hatch of normally developed free embryos was highest in unburied treatments where embryos were incubated on substrates and not covered with sediments and ranged from 81.0 to 87.1% for shovelnose sturgeon and 55.2–80.0% for pallid sturgeon. Mean hatch of normal free embryos was lowest where incubating embryos were fully buried by MCS or FSS and ranged from 2.4 to 11.6% for shovelnose sturgeon and 4.8–15.2% for pallid sturgeon. We observed free embryos with physical abnormalities in all treatments; however, the occurrence was most variable in treatments fully and partially buried by MCS. Hatch of both species was also delayed in treatments where embryos were incubated fully and partially buried by MCS. Our results may be useful to estimate the relative suitability of spawning substrates in relevant river reaches.