Conservation and Ecological Genetics of White Sturgeon in the Upper Columbia River

Sturgeons (Acipenseridae) comprise an ancient fish lineage, appearing in the fossil record with their current morphology in the Cretaceous period (~100 mya). There are 25 extant species, which inhabit rivers and estuaries across Eurasia and North America. They are large and long-lived fish, with most species exhibiting adult lengths beyond two meters and lifespans on the order of a century, and display varying levels of polyploidy across (and to a lesser extent within) species. Sturgeons are slow growing, with the onset of reproductive maturity occurring well past ten years of age in most species. They are among the most imperiled groups of animals, with all species being of conservation concern and 16 being critically endangered, a result of anthropogenic pressures being especially detrimental to taxa with long reproductive cycles. Pressures driving sturgeon declines include overfishing for caviar and meat, dam-induced habitat fragmentation and degradation, predation of early life stages by invasive species, and pollution of watersheds. Extirpation has been prevented in multiple species through conservation aquaculture, in which captive-reared offspring, usually produced from broodstock, are released to bolster wild populations.Conservation aquaculture is conducted for multiple populations of the white sturgeon (Acipenser transmonstanus), which inhabits the Columbia, Fraser, and Sacramento-San Joaquin River basins of western North America. For this species, this measure largely addresses insufficient recruitment resulting from excess mortality in early life stages, which has been linked to dam-induced habitat impacts and predation by invasive species. A conservation aquaculture program targeting the Upper Columbia River population transitioned from broodstock-produced offspring to offspring collected as embryos and larvae from wild spawning events, as the latter approach can potentially represent more parents and greater genetic diversity than the former. Here I present my analysis of this program to evaluate genetic diversity preservation and identify practices that maximize such preservation. First, I demonstrate best practices for sibship inference with polyploid taxa so that spawners represented by wild-origin offspring cohorts can be accurately quantified. Next, I display my genetic evaluation of the conservation aquaculture program, establishing that its utilization of wild-origin offspring has represented far more spawners than its previous broodstock approach and has effectively captured the wild population’s level of genetic heterozygosity. In this evaluation, I further show that mortality of offspring in aquaculture has caused mild to moderate declines in spawner representation and that downstream larval dispersal resulted in little redundancy in sibling families collected from different sites. Finally, I present parentage analysis between wild-origin aquaculture offspring and wild adults, identifying individual adults as having contributed to recorded spawning events from which offspring were collected. Through this approach, I document incomplete spawning site fidelity and females spawning significantly less frequently and for much shorter durations than males, illustrating the significance of collecting offspring across spawning sites, spawning periods, and years to maximize spawner representation in conservation aquaculture. These results directly inform adaptive management of this program and highlight practices maximizing genetic diversity preservation that can be applied to conservation aquaculture of imperiled populations of sturgeons across the world.

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