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Stretching the Shallows
"Shallow water habitat" is the latest buzzword on the restoration scene, with CALFED (see cover) planning to create or restore approximately 20 miles of sloughs and 12,000 acres of shallow water in areas like the Delta, Suisun Bay, San Pablo Bay, the Napa River, Sonoma Creek, and the Petaluma River. Despite the big buzz on the shallows, however, scientists and planners still seem to be struggling to define and understand their role in the grand scheme of life in the Estuary.
"It's almost like a cult has developed around the idea of shallow water habitat," says the Department of Water Resources' Leo Winternitz, part of a new interagency team tracking shallow water habitat restoration. "Lots of questions and assumptions are being made. But I haven't seen any indication that just because you restore all this stuff everything will come back."
So what exactly is shallow water habitat? At the most basic level, it can be defined as water less than 2 meters (about six and a half feet). This is one reason not much is known about it, since most research vessels can't negotiate water less than 10 feet deep. Beyond the commonality of its depth, shallow water habitat can be tidal or non-tidal, perennial or seasonal, salty, fresh or brackish, or vegetated or non-vegetated. The term also refers to channels, sloughs, and dead-end sloughs. All shallow water habitat is assumed to be important for fish.
"During the last five years shallow water habitat has become a big issue, especially with regard to declining species," explains Winternitz. "In the '60s and '70s conditions were pretty good in the Delta. How much shallow water habitat has been lost since then? Not that much- the real losses occurred before the 1960s during the days of Delta reclamation."
Winternitz questions whether restoring shallow water habitat is a panacea to our endangered species problem. "Will we get our target species back or a greater abundance of introduced species? Striped bass like shallow water too. Some people want to swap existing wetlands for tidal shallow water habitat-wetland versus wetland. I don't know if that's good either," he says.
What biologists and ecologists do know is that, depending on their needs and adaptations, many fish, birds, and other wildlife will use shallow water. BurRec's Larry Brown explains that species like splittail seem to require flooded river floodplains upstream of the Delta (such as the Yolo Bypass) for successful spawning, while Delta smelt use shallow water habitat lower in the Delta, such as Cache Slough, and splittail juveniles, tule perch, and prickly sculpin prefer dead-end sloughs- quiet backwaters thought to be particularly valuable for native fish.
Because they are both preferred by native fish and have been especially degraded in the estuarine system, dead-end sloughs may be one of the most important types of shallow water habitat to restore. But the name "dead-end slough" is misleading, explains UC Davis' Peter Moyle. "They are not at all 'dead'; they're full of life. Nor do most of them just end. They're called 'dead-end' because you can't go any further up them in a boat. But there are often streams flowing into them," he says. Moyle has sampled the sloughs in Suisun Marsh and found high concentrations of native fish in them, particularly younger, smaller fish. "They seem to prefer these areas because they're complex habitats with lots of cover (like tules and partly-fallen trees), and food concentrated there," he says.
A few sloughs, like Hog Slough in the Delta, do actually dead-end, Moyle says, but they are also very rich habitat for fish. Temperatures in these shallow sloughs tend to be warmer, which attracts species like large-mouth bass and sunfish.
Restoration of sloughs offer hope for native fish recovery because, as Brown puts it, "that's what used to be there." Shallow water habitat restoration is relatively new but not untried. Several Delta islands are now being flooded for this purpose. On the North Delta's 1200-acre Prospect Island, the January 1997 storms breached the Miner Slough levee in two locations, flooding the area. Project managers are now helping the site along by creating channels and internal islands. In the west and central Delta on Donlon and Venice Islands, shallows were created using dredge spoils to achieve the desired two meter depth. According to Winternitz, informal surveys show that fish and wildlife have begun using these areas and the new team will be watching closely for other progress.
Contact: Larry Brown (916)978-5043 or Leo Winternitz (916)227-7548
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