Physical characteristics and simulated transport of pallid sturgeon and shovelnose sturgeon eggs

Abstract

The imperiled pallid sturgeon (Scaphirhynchus albus) and closely related, but more common, shovelnose sturgeon (S. platorynchus) are believed to broadcast adhesive, demersal eggs in the current and over coarse substrate in turbid rivers of the North American midcontinent. It has been hypothesized that eggs settle immediately following fertilization, but field conditions preclude direct observation. We conducted laboratory studies to characterize the diameter, shape, settling velocity, and specific gravity of pallid sturgeon and shovelnose sturgeon eggs. Based on these laboratory measurements, we then modeled the potential fate of pallid sturgeon eggs by considering these physical properties in the context of two field sites where spawning has occurred. Although eggs of pallid sturgeon and shovelnose sturgeon were of a similar size and shape, shovelnose sturgeon eggs had slightly higher specific gravity and settling velocity. For representative hydraulic conditions at documented spawning sites in the mainstem Missouri and Lower Yellowstone Rivers, eggs of both species will likely be concentrated near the bed although some eggs may be distributed throughout the water column. Simulations of egg transport indicate that eggs may be transported up to several hundred meters downstream from spawning locations in the approximate length of time required for eggs to become adhesive. Estimates of egg transport presented here rely on simplifying assumptions about river hydraulics and limited understanding of how eggs interact with the complex substrates and flow near the bed; results highlight the need for additional studies to evaluate the fate of eggs and fertilized embryos of both species.

Reproductive status of a remnant Lake sturgeon (Acipenser fulvescens) population: Spawning and larval drift in the lower Fox River, Wisconsin

“…In the LFR in 2019, for example, the majority of females spawned in a localized shoreline section representing only 27% of the nearshore cobble spawning habitat. While this concentrated spawning effort may be beneficial in some ways such as increased egg fertilization or increasing individual mating opportunities, it may also lead to excessive egg overcrowding which has been shown to increase the probability of egg mortality (Khoroshko & Vlasenko, 1970; McAdam et al, 2005; Dumont et al, 2011; White Sturgeon, Crossman & Hildebrand, 2014; Fischer et al, 2018; McAdam et al, 2018; Pallid Sturgeon & Shovelnose Sturgeon, Chojnacki et al, 2020). The narrow swath of spawning habitat along the LFR eastern shoreline (in the upstream/downstream direction) also limits the probability that downstream drifting eggs will settle in areas suitable for incubation (Finley et al, 2018).…”