California's intensifying drought is forcing water managers to make tough choices that pit fish species against one another for survival.
In the grip of a three-year dry period that shows no signs of abating, California is butting up against the limits of its vast system of canals, dams and reservoirs, designed to funnel water from northern rivers to farms and cities farther south.
Water managers typically walk a delicate line between supplying water to residents and holding enough in reserve to send down rivers in the summer, when fish are migrating back up from the ocean to lay eggs. With water levels around the state at historic lows, state and federal officials have to decide how to protect fish at varying points in their life cycles.
"Right now, we cannot move water in a way that is safe for fish, but is also necessary to ride out these dry periods without significant economic disruption," state Natural Resources Secretary John Laird said in a statement last week, after snow surveys revealed that snowpack levels are the lowest on record, at 20 percent of average for this time of year (E&ENews PM, Jan. 3).
Yesterday, the federal Bureau of Reclamation cut back water releases from the Nimbus Dam on the American River in order to save water for steelhead salmon that are expected to lay eggs in the river later this month.
The agency is ramping down flows from 1,100 to 500 cubic feet per second (cfs) by Friday to compensate for low storage levels elsewhere on the river. Folsom Reservoir currently holds 178,000 acre-feet of water, just 18 percent of its capacity.
The cutbacks may help the steelhead, which are listed as threatened under the Endangered Species Act. But they're likely to harm another fish: the fall-run chinook salmon, which are just finishing laying eggs in the river's gravel streambed. Without steady flows, areas that salmon had found suitable for egg habitat eventually dry up, killing the eggs.
"The flows that we had on the river when the chinook spawned were predominantly about 1,300 cfs, so we're looking at a major reduction, which is going to most definitely be leaving some of the production from this fall high and dry," said Rob Titus, a senior environmental scientist with the Department of Fish and Wildlife.
The cutbacks could also harm young steelhead, which are still in the river after hatching last year. Higher flows help them move downstream and also help them spread out so they're not all concentrated in one spot, which makes them more attractive to birds of prey.
On Sunday, the Bureau of Reclamation cut flows in the upper Sacramento River to the lowest levels permitted under the Endangered Species Act, which protects the threatened winter- and spring-run chinook salmon. At 3,250 cfs, "they're at the lowest flow they can realistically go to," said Doug Killam, a DFW environmental scientist.
Twenty to 40 percent of the egg deposits left by fall-run chinook, known as "redds," have dried out on that stretch of the Sacramento, according to Killam's surveys and modeling.
"What we're finding is a lot of the redds don't have anything in them," he said. "What was in them had died and rotted away a long time ago."
On the American, projections show that about 14 percent of chinook redds could dry out at the flow levels Reclamation has planned.
"This is the most extreme year that I've ever seen," said Bruce Oppenheim, a fisheries biologist for the National Marine Fisheries Service. "We're experiencing conditions that are worse than 1977, which is the historical driest year on record."
While last year was the driest year on record for the state, there was some water stored in reservoirs from a brief wet period in late 2012. Now, after months of little to no rain, storage is also at historic low levels.
"Last year, things seemed to be fine, by and large," said Peter Moyle, a fish biologist and associate director of the University of California, Davis' Center for Watershed Sciences. "This year, fish are just going to have a really hard time."
While fish are adapted to be able to survive from wet to dry years, California has made it harder for them in dry years by installing dams that prevent them from getting to pools of water downstream.
"We have this fragmented landscape," Moyle said. "From the fish's perspective, there's less hope of recolonization."
That's a key difference between now and the last time the state underwent widespread, record-setting drought, in 1976-1977.
"The system has really changed a lot," said DFW's Killam. "The state has really developed its water resources, and more and more people use it. We're definitely kind of running scared and in uncharted water right now. There's going to be a lot more kinds of these problems cropping up if this drought continues the way it is, where we're having zero rain up here."
In a drought situation, solutions are scant. Fish experts say maintaining steady flows from the beginning to the end of a migration season is key.
"If you're looking for a solution to the problem of dewatering redds, you choose a flow that you can maintain the whole season if there is no other rain," Killam said. "That really is the solution to the problem. If you don't lower the flow on it, that redd is pretty much assured to be successful, given good water quality."
Fishermen say there's more that can be done to save fish. They're hoping DFW will load state-reared baby salmon into trucks and drive them past areas of low flows to wider, deeper parts of the river, rather than releasing them right at fish hatcheries on tributaries.
DFW is planning to release 750,000 juvenile chinook into Battle Creek, a tributary of the Sacramento, next week. Officials say trucking disrupts the salmons' natural migration cycle and makes it harder for them to return to their birthplace to spawn.
But fishing groups say trucking gives the fish the best chance of survival. "These fish evolved to be flushed out of their areas of birth to the ocean in high rain and runoff events," said John McManus, executive director of the Golden Gate Salmon Association. "Right now, the water's really low, really clear, and the birds have an easy time seeing these fish and have a field day with them."
There is one silver lining to the drought: DFW has been tagging juvenile steelhead in the American River for the past few years, which will allow scientists to get a good look at how dry conditions affect survival. "In a sense, we've got a pretty good experiment going that's dictated by nature to be able to look at that comparative survival," Titus said.