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

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Sacramento splittail | Photo: USFWS/Flickr/Creative Commons License
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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.

The Chinook salmon, the Delta smelt, and a couple other fish like striped bass and sturgeon seem to get all the glory when it comes to struggling fish in the Bay Delta. But there's a lot more to the declining fish populations of California's beating heart than those few celebrities.

Take, for example, the Sacramento splittail, a relative of carp that once ranged throughout the Central Valley's watercourses. The splittail was once abundant enough to provide a substantial Native fishery; abundant splittail bones have been found in middens at Native settlement sites along the shores of the former Tulare Lake.

Now, the splittail is restricted to the Delta and interior portions of the Bay. Its numbers are but a fraction of the species' former population and getting smaller. But it isn't protected under either the state or federal Endangered Species Acts...and when the U.S. Fish and Wildlife Service attempted to list it 15 years ago, a bit of pressure from water companies made the agency change its mind.

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Pogonichthys macrolepidotus, as the splittail is known to science, is an attractive silver-gray fish that can reach about 15 inches long. A habitue of slow-moving water in stagnant channels, the splittail lives on microfauna such as insects, small clams and crustaceans, and -- when flood season allows it access to submerged grasslands -- earthworms. But by far the splittail's favorite food is the opossum shrimp Neomysis mercedis.

That favorite food is essentially gone from the Bay Delta. Neomysis mercedis lives primarily on plankton, and the plankton content of the Bay Delta has dropped drastically for a number of reasons, including the introduction of exotic clams that suck up all the plankton in the water.

Fortunately for the splittail, it has discovered it can subsist on one of those clams, the Amur River clam Corbula amurensis.

In addition to its food supply being undermined, the splittail has also, like the Delta's Chinook and other fish, been deprived of its spawning habitat. Unlike anadromous fish that head as far upstream as possible to spawn, splittails rely on floodplains toward the bottom of the river valley, just a little upstream from the Central Delta. Seasonal flooding of wetlands and grasslands provided the splittail with places to lay eggs, in protected submerged vegetation that mostly wouldn't dry out too quickly for the juveniles to swim back to permanent water. But in the last 150 years, we've diked off most of those seasonal floodplains to keep them dry during all but the worst floods.

Water exports from the Delta are a problem, of course. Not only do our diversions reduce the amount of fresh water in the system and alter the region's hydrology, to the detriment of the fish, but the pumps themselves can cause immense damage to the juvenile splittails. In one six-week period in 2011, according to the Bureau of Reclamation, the pumps of the Central Valley Project and State Water Project killed about 6.5 million juvenile splittail. And that was after several years of dramatic decline in the fish's numbers.

Though splittail are still found outside the Delta in Suisun Bay and the marshes north of San Pablo Bay, their numbers have dwindled to the point where there are few splittail connecting the easternmost and westernmost populations. A recent study showed that splittail in the Napa and Petaluma Rivers have developed significant genetic differences from their Delta cousins, an indication of reproductive isolation. The near-continuous historic populations of the fish in freshwater marshes along the North Bay shorelines would likely have prevented such isolation.

None of this is news to fisheries folk. Concern about the decline of Sacramento splittail was significant enough that wildlife protection groups the Center for Biological Diversity and the Natural Heritage Institute petitioned to list the species under the U.S. Endangered Species Act in 1992. In 1994, USFWS responded to that petition by proposing to list the splittail as threatened. It took five years and a lawsuit by the Center and the Sierra Club to make that listing actually happen, in 1999. In the following year, water agencies sued USFWS to reverse the listing. A court ordered USFWS to review the listing, and in 2004 -- in a move widely interpreted as a Bush Administration concession to industry -- USFWS reversed itself and decided the splittail wasn't in need of protection.

Eleven years on, that's where the splittail stands.

The good news is that, should the USFWS decide to protect the Sacramento splittail, it might not take long to get the fish's numbers climbing again. Splittails mature sexually at two years of age and can produce lots of offspring each year. And the floodplains they require as spawning habitat, if expanded and gven water, would also boost the phytoplankton in the Delta that those invasive clams have been vacuuming up.

That is, of course, assuming both the political will to save the splittail and an easing of the drought, and it's hard to figure which condition is more likely to come first. Without both, the Sacramento splittail's fate may match that of its closest cousin, the Clear Lake splittail Pogonichthys ciscoides, last seen in the 1970s and now presumed extinct.

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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