California's Delta: Inside and Out
6:00 am
Tue October 15, 2013

California Water Series Part 2: The Delta's Fragile Ecology

The Sacramento-San Joaquin Delta was once a vast tidal marshland and inland estuary. Now thousands of miles of fragile levees surround artificial islands below sea level. More than 90 percent of wetlands have disappeared, and native fish are dying.

Suisun Marsh is the largest brackish water marsh on the West Coast. It’s at the Delta’s western most edge.  University of California Davis researchers set out on a boat in Montezuma Slough, which connects the Sacramento River to Suisun Bay.

“It’s a place where fish can easily have access to if they’re migrating up and down the river,” says Peter Moyle, a professor of fish biology for UC Davis. He has been sampling fish in Suisun Marsh every month for the past 34 years.  “This is same delivery system makes it possible for small fish to come and get in here to rear and move out again.”

Moyle says it’s also one of the most biologically productive areas, not just for fish, but for otters, birds, and all kinds of invertebrates.

“It’s used by sturgeon and salmon and many other species,” he says. “Over the years we’ve gotten 50 species of fish out here. On a typical sampling day we’ll get 15 to 20 species of fish, and about half of them are native, half of them are non-native.”

Invasive species problem for Delta

Researchers pull traps used to catch small bottom-dwelling fish.

“This right here is a Siberian prawn, invaded about 10 years ago from China,” Moyle says as he holds up a translucent shrimp. He then picks up a clear jellyfish a little bigger than a quarter. “This is a jellyfish that’s native to the Black Sea,” he laughs.

Most of the invasives come into the estuary through ship ballast water. Moyle says the Delta’s ecosystem is complex and constantly changing. Over the years, he’s made troubling discoveries.

“I was tracking the Delta smelt as one of the many species that we were catching here and I noticed that in the mid-1980’s that their populations had started to go into decline,” he says. “Then in a couple of years they just about disappeared from our samples.”

The Delta smelt was soon listed as threatened under the Endangered Species Act. It joined other Delta species, including winter-run chinook salmon, longfin smelt and green sturgeon.

The reasons for the population declines vary. Invasives are part of the problem. The overbite clam consumes the Delta smelt’s food. Sewage treatment plants have polluted the water. And then there are the pumping plants in the south Delta.

“You remember the scene in Star Wars where the Millenium Falcon and Han Solo are flying by the Death Star?” asks Chuck Bonham, director of the California Department of Fish and Wildlife. “And all of sudden the tractor beam force-field comes out of the Death Star and it just pulls the Millenium Falcon in? We’ve got that same scenario going on with these large pumps. They literally pull the fish off their natural migration paths, down to the pumps, and when they get down there, two out of three of them die.”

Salmon Fishermen Affected by Delta

Salmon fishermen have seen the results first hand. Pietro Parravano was a commercial salmon fisherman for 20 years before becoming President of the Institute for Fisheries Resources. He sits on his boat in Half Moon Bay.

“Salmon is a perfect example of what happens when things change or altered in terms of habitat. There are still hundreds of thousands of salmon that die because of the dams and the pumps,” says Parravano.

The pumps cause reverse flows in the estuary. That confuses salmon whose natural instinct is to follow the flow. Zeke Grader with the Pacific Coast Federation of Fishermen’s Associations says the Delta and Central Valley provide about 90 percent of California’s overall salmon production. He says any changes there can affect salmon fishing from the Santa Barbara coast to Crescent City.

“The state water project and the federal water project combined have made a big hit on the whole ecosystem whether it’s a direct changing of flows in the system or affecting the habitat or viability of this estuary,” says Grader.

The Bay Delta Conservation Plan proposes two tunnels that would pump water out of the Sacramento River instead of the southern Delta.

“The bigger run in the Central Valley system comes out of the Sacramento, not the San Joaquin,” says Grader. “So you’re potentially putting at risk of your bigger salmon population.”

It also has the potential to increase the Delta’s salinity.

“We worry about it,” says Chuck Bonham, with the California Department of Fish and Wildlife. “Those potential new diversions from the Sacramento, they’re going to have to be up to snuff. And that’s a regulatory burden we expect the Department of Water Resources and the Bureau [of Reclamation] to understand and then work with us on meeting.”

Peter Moyle says in theory the tunnels could work.

“The assurances are always given that if we build these tunnels they’ll be operated in a fish-friendly way,” says Moyle. “Maybe we just have to believe that. But that’s a big ‘if’,” says Moyle.

He says successful habitat restoration for fish and other species will be crucial. The Bay Delta Conservation Plan proposes to restore 145,000 acres. 

Video of boat ride on Suisun Marsh by Amy Quinton

Video of salmon at Oroville Dam by Amy Quinton

Related Program