2017 turned out to be a good year for the white
sturgeon in the middle Snake River, says Idaho Department of Fish and Game. In
the river between Bliss Dam and CJ Strike Reservoir, sturgeon took advantage of
the rare high river flows and spawned successfully in the spring.
These sturgeon might only reproduce
successfully every 3-5 years, if that. In some sections, white sturgeon face an
uncertain future, because the habitat and river flows they need to reproduce
have significantly changed as the Snake River has been developed.
In Idaho, sturgeon are found along the Snake
River from Twin Falls to Lewiston. But they only reproduce naturally in two
sections: below Bliss Dam and in Hells Canyon.
Sturgeon thrive in long sections of
free-flowing rivers that have a variety of habitats. To reproduce successfully,
sturgeon need high spring flows to cue spawning and clean gravels to incubate
the eggs. Because of these spawning requirements and changes to river habitat,
successful spawning usually only happens in years with 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.
The big 2017 snowpack brought enough water to
fill the reservoirs and still deliver the big flows needed to clean the river
and help young sturgeon survive.
Idaho Power Co. does most of the sturgeon
research (in cooperation with IDFG) in the middle Snake River as part of their
license to operate dams and generate power. This year, biologists captured tiny
newly hatched larval sturgeon as they drifted down the river during the early
summer. 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 won'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 with little food.
Surveys this fall, says IDFG, showed this new
age class of young sturgeon was surviving well and growing fast. By November,
these young sturgeon were already 12 inches. Once a sturgeon makes it to this
stage, their survival to adulthood is high.
After monitoring sturgeon in the middle Snake
River for many years, biologists have a good sense for what 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.
For more about sturgeon in Idaho see https://idfg.idaho.gov/blog/2016/08/conserving-snake-river-sturgeon-introduction-part-1-7