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Bay Delta Fish You've Never Heard Of: Longfin Smelt

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Longfin smelt | Photo: Rene Reyes, U.S. Bureau of Reclamation
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The Threatened Delta smelt is famous, but there's another smelt in the Bay Delta whose decline is making wildlife partisans worried. The longfin smelt may well have been, a century ago, the most abundant fish of open water in the Bay Delta, with a significant commercial fishery catering to the swelling cities of Northern California.

Now, it's in a club some environmentalists refer to as "Extinction's Waiting Room": the long list of species that the U.S. Fish and Wildlife Service have decided not to list under the Endangered Species Act even though the agency concedes the species merit protection.

It's a dramatic turnaround for what was once a nearly ubiquitous fish in the Bay Delta. And unless the smelt wins protection, that decline may prove irreversible.

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The longfin smelt, Spirinchus thaleichthys, is a bit more than twice the size (at five inches or so) of its more headline-grabbing cousin the Delta smelt. Though they're both members of the smelt family, the Osmeridae, longfin and Delta smelt aren't particularly closely related. The two will mate on occasion, but scientists assume the resulting hybrid offspring aren't fertile.

Like so many other fish found in the Bay Delta ecosystem, longfin smelt are anadromous. They spawn in fresh water, then head for brackish or saline water as adults. In the Bay Delta area, that means adult longfin smelt head out to either San Francisco Bay or the Gulf of The Farallones, that broad bay outside the Golden Gate that stretches from Point Reyes to Pescadero.

Longfin smelt live from one to three years, eating zooplankton and slightly larger crustaceans such as opossum shrimp, and then -- when that mysterious urge strikes -- they head back into freshwater to spawn. Fisheries biologists suspect that the smelts head into the lower reaches of the Sacramento and San Joaquin rivers to spawn, but they're not sure.

Longfin smelt live outside the Bay Delta as well, with populations in river estuaries as far north as Alaska where freshwater and saltwater meet and mix. The population closest to the Bay Delta may be a small outpost at the mouth of the Russian River on the Sonoma County coast, separated by about 50 miles of open ocean from the Bay Delta population, which seems only to get as far north as Stinson Beach. The Russian River estuary is thought to be too small to support a sustainable population of the smelt, and none have been seen there for about 15 years.

The Bay Delta longfin smelt population is the southernmost known, and also the most-studied. While almost nothing is known of the species' numbers from Northern California through Alaska, the Bay Delta longfin smelts have been the subject of population surveys since the 1960s. That half century of data has taught us a few things, including an apparent correlation between freshwater flow and smelt numbers. The more fresh water that comes through the Delta on its way out to the Bay, the more longfin smelts there will be.

As the longfin smelt is able to produce a lot of offspring, the species' numbers can jump dramatically within a couple of years when conditions are favorable. But since the adults only live a couple of years and die after spawning, the longfin smelt population can crash pretty hard when times are bad.

And that capacity for wild swings in numbers shows up clearly in the last half-century of data. But in the last 15 years, the smelt has stopped gaining in number during wet years.

The reason, according to the U.S. Fish and Wildlife Service, is the decline in plankton that's plaguing a number of fish species in the Bay Delta, mainly caused by the proliferation of two invasive species of Asian clams. Annual mid-water trawl sample counts show significant boom years for the smelt in the first decades of study, with counts above 50,000 in 1966, 1969, and 1982. Since 1995 no count has come close to breaking the 10,000 mark, with just 13 longfin smelt counted in 2007. In 2011, a relatively wet year in mid-drought, the count rebounded to 477. 2014's count was 16.

Those aren't complete censuses: the trawls certainly don't catch all the longfin smelts in the Bay Delta, as evidenced by the fact that hundreds of longfin smelts die at the Central Valley's water project pumps in many months when the trawls count fewer smelt than that. But the trawls offer a sample-style survey of relative abundance, and for the last 15 years it's been bad news.

Between the ecosystem collapse and lack of planktonic food wrought by the clams, and the drought's ongoing low freshwater flows exacerbated by continued diversions for municipal and irrigation water, in other words, the Bay Delta population of longfin smelt is in trouble. In 2007, environmental groups petitioned the U.S. Fish and Wildlife Service to protect the Bay Delta population of longfin smelt under the U.S. Endangered Species Act. Two years later USFWS declined to list the fish in the Bay Delta, saying that Bay Delta longfin smelts weren't distinct enough from the rest of the species to be listed separately.

Activists and fisheries biologists pointed out that there was essentially zero chance the Bay Delta longfin smelts were breeding with smelts elsewhere. In 2012, USFWS agreed, saying that the Bay Delta population -- which it deemed the San Francisco Bay-Delta longfin smelt Distinct Population Segment -- did indeed deserve to be listed, but the agency said other species in worse trouble were higher on its priority list.

The longfin smelt was put on USFWS' "Warranted but Precluded" candidate list, a bit of agency jargon that essentially means "no, seriously, we'll get to it as soon as we can." Some species placed on the Warranted But Precluded list have stayed there for many years.

The state of California did manage to list the longfin smelt as Threatened under the California Endangered Species Act in 2009, which makes it illegal to kill the smelts anywhere in the state without a permit. But that hasn't prevented bycatch from other fisheries in the Bay and Delta. Shrimp trawlers and bait fishing boats caught thousands of longfin smelts by mistake in the early part of this century, likely contributing to the species' decline.

As freshwater flows through the Delta decline with each passing year of drought, the plight of the Delta's longfin smelt likely worsens. A listing under the federal Endangered Species Act would make it that much harder to divert even more water from the Delta for cities and farms. That's unlikely to be a popular solution, but it may be the only thing that will save the longfin smelt.

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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