Delta smelt population on the rise, survey finds

Oct 14, 2011 By Bettina Boxall

The imperiled fish that has been at the center of California's water wars may be at its highest numbers in a decade, judging by the results of a recent survey.

Every month in the fall, state biologists tow nets in the Sacramento-San Joaquin , sampling for the threatened delta smelt to estimate the native fish's population. The September catch this year, though still small by historic standards, was the biggest since 2001, when the numbers of smelt and other delta fish started to plunge to dangerously low levels, triggering cutbacks to customers in the Central Valley and Southern California.

Biologists attribute the uptick to a variety of factors, many tied to the surge of water that a wet winter and spring sent into the delta. Abundant flows in the smelt's only home meant more food, less competition from an invasive clam and less chance of run-ins with the huge delta pumps that export water south.

With three more months of sampling left, it's too early to say if the smelt count signifies a rebound for the species. "We'll see," said Roger Patterson, assistant general manager of the Metropolitan Water District of Southern California, which has been hurt by pumping curbs imposed to protect the smelt and migrating salmon.

Doug Obegi, an attorney with the Council, called the September numbers "very, very encouraging."

"I think it does show that the species is not past the brink, and when we add water, the estuary does recover and the species does recover," Obegi said. He added: "It's politically easier to do that in a wet year."

Most smelt live for only a year. The fall trawls sample fish born in the spring that will spawn next year, so they are vital to the population.

The catch is used to calculate an abundance index. Last month's index was 50, compared with six in September 2010. The year before that, the September index was one, the lowest in four decades of collections.

Randall Baxter, a senior biologist with the state Department of Fish and Game, said no single factor could explain the jump.

Last winter, he said, adult smelt didn't congregate near the pumps, because of high flows from the into the south delta and because "the fish just chose different locations to spawn in."

He also speculated that the large volume of water flowing into the delta diluted ammonia released from a Sacramento-area sewage treatment plant, boosting production of algae and organisms at the base of the delta's food chain.

The strong flows carried fish and larvae into Suisun Bay, which provides some of the best smelt habitat remaining in the much altered ecosystem. And they likely hindered the feeding and reproduction of an invasive clam that competes with smelt for food.

Baxter was hopeful that September's good news will last. "Because the water conditions have persisted, there is a good chance that we'll continue to see similar numbers of delta smelt through time this fall."

The year isn't just looking good for delta smelt. The numbers of several other delta species, including longfin smelt and striped bass, are also up.

Explore further: Five anthropogenic factors that will radically alter northern forests in 50 years

5 /5 (1 vote)
add to favorites email to friend print save as pdf

Related Stories

A small fish caught in a big fuss

Feb 08, 2011

When Peter Moyle began studying an obscure little Northern California fish in the early 1970s, he had no inkling of the role it would come to play in the state.

Feds release Calif. plan to protect chinook salmon

Jun 04, 2009

(AP) -- Federal fisheries regulators on Thursday released a court-ordered plan to help struggling chinook salmon that includes opening California dams and restricting pumping, which would reduce the amount of water available ...

Recommended for you

More, bigger wildfires burning western US, study shows

15 hours ago

Wildfires across the western United States have been getting bigger and more frequent over the last 30 years – a trend that could continue as climate change causes temperatures to rise and drought to become ...

User comments : 0

More news stories

Six Nepalese dead, six missing in Everest avalanche

At least six Nepalese climbing guides have been killed and six others are missing after an avalanche struck Mount Everest early Friday in one of the deadliest accidents on the world's highest peak, officials ...

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

There's something ancient in the icebox

Glaciers are commonly thought to work like a belt sander. As they move over the land they scrape off everything—vegetation, soil, and even the top layer of bedrock. So scientists were greatly surprised ...

Clean air: Fewer sources for self-cleaning

Up to now, HONO, also known as nitrous acid, was considered one of the most important sources of hydroxyl radicals (OH), which are regarded as the detergent of the atmosphere, allowing the air to clean itself. ...

Scientists tether lionfish to Cayman reefs

Research done by U.S. scientists in the Cayman Islands suggests that native predators can be trained to gobble up invasive lionfish that colonize regional reefs and voraciously prey on juvenile marine creatures.

Leeches help save woman's ear after pit bull mauling

(HealthDay)—A pit bull attack in July 2013 left a 19-year-old woman with her left ear ripped from her head, leaving an open wound. After preserving the ear, the surgical team started with a reconnection ...