(CN) – Scientists working to preserve endangered fish in the Sacramento River unveiled a new water-management plan Tuesday that might protect the river’s salmon while maintaining a healthy environment for other fish.
As cold water from Lake Shasta releases into the Sacramento River, it creates a better environment for endangered winter-run chinook salmon, but at the cost of harming green sturgeon.
Whereas salmon need colder water for their eggs to survive, young green sturgeon require the typical warmer temperatures of the river to thrive.
In a paper published Tuesday in the Journal of Applied Ecology, scientists at the University of California, Santa Cruz and the National Marine Fisheries Service used statistical modeling to determine an optimal water management plan that would protect both species and ensure other water users would benefit as well.
"It's a win-win-win here in the sense that we're not giving up anything to get an improvement for the green sturgeon," said Eric Palkovacs, senior author and associate professor of ecology and evolutionary biology at UC Santa Cruz. "Currently, the primary management objectives are keeping it cold for the salmon eggs and delivering enough water downstream. As a result, we've been refrigerating the river in regions where historically the green sturgeon have been spawning."
Study author Liam Zarri discovered that water temperatures and discharge rates from the Shasta Dam into the river heavily affected the health of larval green sturgeon.
When a high amount of discharges of cold water happened over the course of a year, survival of winter-run chinook salmon eggs increased while survival of juvenile green sturgeon decreased. In years of drought, with warmer water and low discharge flows, the reverse effect occurred.
Zarri said the key to ensuring both species’ survival was in their different spawn times.
"We're able to suggest a management scenario which uses the differential timing of spawning in these two species. When they overlap, our model gives us the ideal temperature and flow for when both species are present," he said.
Zarri proposes that low flows of warmer water, drawn from the surface of the lake, be released in April and May when only green sturgeon spawn and agricultural demand for water is low. Then from July to November, high flows of cold water can be released in order to ensure the survival of the salmon and meet the water needs for agriculture.
"Under the current management, there is quite a long period of cold water releases starting very early in the season before the chinook salmon have really started showing up in earnest. We're saying that you can wait until the green sturgeon have matured and moved out of the system," Palkovacs said. "That has a side benefit in drought years, when limiting those early releases saves water for later in the year when it's more valuable, both for salmon and for downstream water demand."
The Sacramento River winter-run chinook salmon is one of two chinook salmon species listed as endangered under the Endangered Species Act. Seven others are considered threatened.
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