Dire straits

California native salmon, steelhead and trout could be mostly extinct in a century if current trends continue.

Researchers said in a report last month that up to 74 percent of the fish species could be gone in 100 years—45 percent in 50 years—due to climate change and human activity eliminating habitats throughout the state. Scientists stressed that their estimation is a warning bell to support native fish diversity in general.

“They’re the most charismatic members of stream fauna in California,” said lead researcher Dr. Peter Moyle of UC Davis.“If you protect them, you’re protecting a host of other birds and fish that help ecosystems and people.”

The report is the second from conservation nonprofit CalTrout and UC Davis’ Center for Watershed Sciences. It predicts the decline of 32 species while providing recommendations to save them.

The first report, released in 2008, showed five species that were likely to be extinct over the next five decades. Thanks to five years of drought, that figure nearly tripled to 14 species with the new report, released May 16. The new report cited other threats to the fragile ecosystems, including dams that block access to historical spawning grounds, and agricultural pollution.

The warming climate is reducing the cold water habitat that salmon, steelhead and trout (i.e., salmonids) need. For the Sacramento River, multiple dry years reduced the amount of releasable cold water from Shasta Reservoir, causing warmer water downstream and a more harmful habitat for young salmon and eggs. That likely devastated the population, the report states.

The Sacramento River’s chinook salmon are critically vulnerable due to a high dependence on cold water. Shasta, and Keswick Dam near Redding, prevent access to all historical spawning areas and most nurseries. Nearly a third of the species are now spawned in hatcheries, likely accelerating the extinction of wild salmon.

Asked whether hatcheries could produce the fish if their natural habitats become uninhabitable, CalTrout Executive Director Curtis Knight said cultivating such boutique populations wouldn’t ensure long-term survival.

“We need to have a genetic reservoir for changes we expect to come,” he said. “It’s not just about, can we mechanize our way out of this? Diversity tells us a lot about the health of California and one of our most important resources—cold, clean water.”

The researchers urged farmers and environmentalists to work together. Fields of rice and other crops could be turned into floodplains in off-seasons to support rapid growth of young salmon. That’s already happening on the Yolo Bypass between Davis and Sacramento. Legislators also could prioritize fish pathways to spawning grounds by removing dams and other barriers, and pursue strategies to improve diversity by restoring habitats and creating highly managed ecosystems.

“These fish have gone through earthquakes, climate change and isolation,” said Rob Lusardi, one of the UC Davis report authors. “The reason they’ve been able to is because of diversity. We need to protect that.”

Moyle said the governor’s proposed twin tunnels, which would bring water from the Sacramento River to the San Joaquin Valley and Southern California cities, might be essential for the future of fish in the delta.

He expects levees around islands will give way at some point, changing the delta’s water dynamics and threatening the ability of large pumps to export fresh water. If that happens, Moyle said, political pressure will mount to reconnect the Sacramento River to pumping plants on an emergency basis. That, in turn, would create a system of canals that would be the worst situation for fish to migrate through.

Instead, the twin tunnel entrances would include fish screens and water exports would be kept at a similar level to what they are now, reducing the possibility of fish being sent to unfavorable habitats in the central and south deltas.

However, Moyle continued, questions remain on how effective the tunnel screens would be because they “rarely work as well as promised.”

Bottom line, he added, “there is still a great deal of uncertainty on the effects of the tunnels, depending on their size and operation. In the long run, properly operated tunnels should benefit salmon and other migratory fish, or at least not make them worse off. But I would not take any bets on it until there are firmer fish-protection measures.”