There are no guarantees for the survival of white sturgeon on the upper Columbia but there’s’ still hope.
The population is dangerously low, but it’s stable enough to have staved off extirpation, giving researchers time to solve the puzzle of why many of these prehistoric fish are dying before they can reproduce.
The current estimate for the Canadian portion of the Columbia River is approximately 1,100 wild adults, with more than 5,500 hatchery-origin sturgeon at large.
“The white sturgeon conservation aquaculture program has been releasing hatchery-raised sturgeon into the Columbia River annually since 2002 and has been very successful,” reads a 2020 BC Hydro water-use plan update. “Monitoring shows that more of the young fish have survived than originally expected.”
The Upper Columbia White Sturgeon Recovery Initiative (UCWSRI) was formed in 2001 by BC Hydro and two dozen partners from government, First Nations, industry and environmental groups in Canada and the U.S. to better understand the impacts of river-flow changes caused by hydroelectric dams built from the 1960s through the 1980s.
The sturgeon population was listed as endangered under the Canadian Species at Risk Act in 2006 due to recruitment failure, when too few fish survive to their reproductive age.
Researchers estimate the wild population once relied on an adult population of 1,500 spawners to maintain group sustainability. Today there are only about 100 adults contributing to spawning events.
The conservation-aquaculture program is focusing on collecting eggs and larvae from the wild for rearing in a hatchery to ensure survivability and genetic diversity.
A decade ago as many as 4,000 hatchery fish were released annually into the Upper Columbia, but today the releases have dropped significantly as researchers record higher survival rates than previously expected, and as they fine tune their understanding of the fish and their habitat.
“The aquaculture program is constantly evolving and adaptively managed in response to new information,” Kevin Aquino, a BC Hydro spokesperson said. “The number of fish released since 2001 has been steadily declining as we learn how well the fish survive following their release. Currently, the release of 200 fish at a minimum body weight of 200 grams is sufficient to meet long-term population targets set in the national recovery strategy.”
Sturgeon can grow up to three metres in length and live up to 100 years. They begin breeding only in their second decade, which underscores the importance and complexity of seeing them through to maturity. Even then, reproduction rates are unpredictable as males breed only every one or two years, and females every three to seven years.
An investigation of spawning sites has revealed one area in the Upper Columbia River that will undergo habitat restoration next year, but there is still no certainty as to why the general population is not procreating successfully.
Scientists have observed thousands of wild-hatched fish move downstream to feed, but are still trying to understand why most don’t survive their first year. Hypotheses centre on the effects of dams changing river flows, and improved clarity of the water reducing the fishes’ ability to hide from predators.
There are also introduced and invasive species of fish in the river system, including walleye, northern pike and smallmouth bass, that prey on the young sturgeon.
In May, 2017, the public was invited to help release 1,800 juvenile sturgeon into Arrow Lakes near Revelstoke, in an effort to create a sub-population of sturgeon as an insurance strategy in case the Upper Columbia population meets a catastrophic end.
To date about 62,000 hatchery sturgeon have been released into the lake, home to about 50 wild adults, but low recapture rates have prevented researchers from estimating hatchery-sturgeon survivability or abundance.
“As a result, we’ve been adapting the hatchery program and the field monitoring accordingly,” Aquino said. “Wild adults are still spawning intermittently near Revelstoke. In recent years, one of the bigger successes in Arrow Lakes has been the transfer of wild-origin progeny — embryos and larvae produced through natural spawning events — to the hatchery for rearing and release. This is similar to the program in the lower Columbia and ensures the genetic diversity of the wild adults is captured in the fish that are released.”