Bay Delta Fish You've Never Heard Of: Sacramento Perch

An explanatory series focusing on one of the most complex issues facing California: water sharing. And at its core is the Sacramento-San Joaquin Bay Delta. Stay with kcet.org/baydelta for all the project's stories.

If any fish native to the Delta seemed tailor-made to withstand the drought, it would have to be the Sacramento perch. Tolerant of a wide range of water quality, the perch can thrive in clear, cold water or warm water so stagnant and thick with algae it would choke a cow. It can survive in slightly brackish water, in water contaminated by runoff, and in muddy ponds only a few inches deep: perfect for the drought-era Delta.

And yet only a few Sacramento perch remain in the native Delta habitat, at best. Widely planted in stockponds and reservoirs outside its native range, the perch is functionally extinct in the Delta and throughout the rest of its limited original range.

As is so often the case with common names, the Sacramento perch isn't actually a true perch. Known to science as Archoplites interruptus, it's a member of the sunfish family, Centrarchidae, along with bluegills and largemouth bass. In fact, it's the only member of that family native to North America west of the Rocky Mountains, and has evolved without having to compete with other members of the sunfish family for food or habitat, perhaps since the Miocene Epoch, which ended 5.3 million years ago.

The Sacramento perch wasn't picky about that habitat. In addition to the streams of the Delta and Central Valley, Archoplites once thrived in the Salinas and Pajaro rivers in the Monterey Bay area, as well as in Clear Lake. Though the perch did swim in clear, swift-flowing water, it seemed to prefer the other kind: stagnant pools and side-channels, sloughs viscid with algae, ponds choked with emergent vegetation.

The Sacramento perch's wide tolerance of water conditions includes temperature. The adults can survive in water far warmer than many other Delta fish can tolerate: until the water reaches about 72° Fahrenheit, adult Sacramento perch do just fine. Warmer than that, and the adults will decline in fitness, leaving to cooler waters if they can.The perch's larvae can tolerate even warmer water. That's a good thing, because heavily vegetated, shallow, and turbid waters are where Sacramento perch tend to spawn. Vegetation slows water currents, and suspended silt and organic matter absorb sunlight, both process warming the water.

The perch spawn in loose schools, likely due less to any innate gregariousness than to multiple fish finding a location favorable. Unlike other sunfish family members, the males don't spend time preparing a nest. Instead, females lay their eggs in a likely patch of submerged, vegetated silt and one or more males will fertilize the eggs.

Male Sacramento perch are negligent fathers, at least by sunfish family standards. Perhaps because they went at least 5.3 million years without competition from other sunfishes for nest sites, male perch don't guard their nests after the eggs hatch, leaving their larvae vulnerable to predation. They're also pretty easy to chase off their nests before the eggs hatch. (To be fair in this application of human standards to fish childrearing practices, the females leave the nests immediately after spawning.)

That seems to be part of the problem with the Sacramento perch disappearing from the Delta: introduced fish such as carp and catfish can chase the males off their nests to eat the eggs, and others move in to eat the larvae once the deadbeat dads leave home after hatching.

And as with just about every other species of fish -- and species of not-fish -- native to the Delta, our massive reengineering of the region's waterworks plays a role as well. There are fewer stagnant sloughs with fringing, seasonally flooded wetlands in which the Sacramento perch can spawn and grow.

But one problem that seems specific to the perch is competition for habitat from introduced members of the sunfish family, such as the bluegill and green sunfish. Such introduced sunfish tend to be more aggressive than the Sacramento perch, and they chase the perch away from favored habitat, including spawning sites.

That's borne out by studies of ponds to which the Sacramento perch has been introduced, often as a mosquito control method. (Juvenile perch are voracious eaters of mosquito larvae.) Introduce bluegill or green sunfish into a pond in which the perch are doing well, and the perch start to decline. In a research project in Yolo County, bluegill drove a pond full of perch to extinction in just two years.

At least one sunfish family member seems to get along okay with the perch. At Point Reyes National Seashore, both Sacramento perch and largemouth bass thrived for some time at Abbott's Lagoons.

But that's scant good news. Bluegill in particular have been a problem. Introduced to California waters in the 19th Century, bluegill have spread throughout most of the waters of the state.

The effects on the perch have been dramatic. A survey in 1898-99 cited a commercial perch fishery in the Delta, with more than 400,000 pounds of the fish sold some years in San Francisco markets. By the 1960s, they were nearly gone from the Delta. One adult Sacramento perch was caught in a Sacramento River survey in 1992, but fisheries biologists think it unlikely that a self-sustaining population of the species exists anywhere in the Central Valley. The perch is likewise gone from the Salinas and Pajaro rivers, and adults are found now and then in Clear Lake -- possibly escapees from farm ponds.

The species isn't extinct. Aside from those farm ponds up and down the length of California, planted populations still survive in several large reservoirs, including the San Luis Reservoir in Merced County, and alkaline lakes such as Pyramid Lake north of Reno, Nevada.

Essentially extinct in its native range since before passage of the U.S. Endangered Species Act in 1973, the Sacramento perch is neither listed nor protected under that law. The remaining perch in Clear Lake, if any, are considered a California Species of Special Concern, a status that prompts the state to enact management measures to protect the species.

What can be done, if anything, to restore the perch to its native habitat? A recovery plan for Delta native fish species published nearly 20 years ago by the U.S. Fish and Wildlife Service suggests that flooding islands in the Delta to provide shallow water habitat might well be the answer, if it's done with careful attention paid to controlling the perch's competitors. While USFWS admitted the Sacramento perch has "low restoration potential," it suggested that reclaiming diked islands might provide the perch with some of its preferred habitat for spawning and just generally hanging out. The two islands it mentioned, Liberty and Prospect islands north of Rio Vista, have since been restored as tidal wetland.

Some of the ponds the perch lives in are within swimming distance of those islands. Others live in maintained wetlands in the Yolo Bypass wildlife area, closer to Sacramento. There are Sacramento perch in ponds on the UC Davis campus that occasionally escape into nearby Putah Creek, a Delta tributary. The Sacramento perch might just come back someday after all, given half a chance.