2017 turned out to be a good year for the white sturgeon in the middle Snake River. In the section between Bliss Dam and C.J. Strike Reservoir, sturgeon took advantage of the rare, high spring-flows and spawned successfully.
It’s an exciting time because sturgeon might only reproduce successfully every three-to-five years, if that, depending on river flows.
In some sections of the Snake River, white sturgeon face an uncertain future because the habitat and river flows they need to reproduce have significantly changed as the river has been developed.
Sturgeon are found in the Snake River from Twin Falls to Lewiston. That’s a lot of river, but they only reproduce in two sections: below Bliss Dam and in Hells Canyon. The Snake River is one of the most dammed rivers in the country.
Dams provide many benefits, such as irrigation for agriculture, electricity generation and reduced flood risk. But the benefits also come at a cost to migratory fish, including white sturgeon.
Sturgeon thrive in long sections of free-flowing rivers that have a variety of habitats. To reproduce successfully, sturgeon need high spring-flows that cue fish to spawn and clean gravels to protect and incubate the eggs.
Because of these spawning requirements and historic changes to the river habitat, successful spawning usually only happens when there are very high river flows.
In most years, upstream dams capture most of the runoff, so flows in the middle Snake River don’t get high enough for sturgeon to successfully spawn.
But the big 2017 snowpack brought enough water to fill the reservoirs and still deliver big flows needed to clean gravel and help young sturgeon survive.
Idaho Power does most of the sturgeon research in cooperation with Fish and Game in the middle Snake River as part of the company’s license to operate dams and generate power.
In summer 2017, biologists captured newly hatched larval sturgeon as they drifted down the river. While that’s a good sign, finding larval sturgeon doesn’t necessarily mean successful reproduction.
In many years, adult sturgeon spawn, but the tiny larval sturgeon don’t survive unless river conditions are just right. Larval sturgeon are easy food for predators, or may starve if they drift into poor, slack-water habitat.
Surveys during fall showed this healthy new age class of young sturgeon survived and grew fast. By November, these young sturgeon were already 12-inches long, which is incredibly fast growth for a fish less than 6 months old.
Once a sturgeon makes it to this stage, their survival to adulthood is very high, so we expect to see these fish in the river for years, if not decades, to come.
After monitoring sturgeon in the middle Snake River for many years, biologists have a good sense for the recipe that sturgeon need for spawning. River flows of at least 15,000 cubic feet per second below Bliss Dam combined with the right water temperatures in May and June seem to be the ticket.
Unfortunately, this combination is happening less often. Idaho’s weather patterns are changing, and that is affecting the amount of snow and rainfall in the Snake River Basin.
Dams can capture most of the runoff, so the high flows needed for spawning only occur in years with really big snowpacks when runoff produces more water than the dams can hold. These changes mean the high spring flows needed to sustain sturgeon reproduction are happening with less frequency.