Using a semi-natural stream to produce young sturgeons for conservation stocking: Maintaining natural selection during spawning and rearing

Young sturgeons used for conservation stocking are presently produced using the same methods used for commercial culture. To determine if young sturgeons could be produced without relaxing natural selection factors, we developed a semi‐natural stream where we annually studied mating of wild shortnose sturgeon (Acipenser brevirostrum) observed movement of gametes released freely during spawning, and estimated the number of larvae produced by various densities of spawned eggs. The stream had a bottom area of 18.8 m², a rubble–gravel bottom, and a mean bottom current at 0.6 depth during spawning of 48 cm s⁻¹ (range, 17–126 cm s⁻¹). Wild adults successfully spawned in the stream each year for 7 years (2002–2008). Some females and males were more successful during spawning than others, suggesting an unequal fitness during spawning among wild individuals, which is different than the controlled spawning fitness of individuals in hatcheries. Male and female gametes spawned naturally must connect quickly in the fast current or fail, a selection factor absent in hatcheries. The number of larvae produced was inversely related to spawned egg density m⁻² (R² = 0.65) and the maximum number of larvae produced was 8000–16 000 (425–851 larvae m⁻² of bottom). Artificial spawning streams have the potential to contribute to sturgeon restoration.