San Joaquin River DOTMDL -- Technical Working Group

$2 million project to analyze the diminution of delta smelt; The sharp drop-off indicates a decline in estuary's health

San Francisco Chronicle - June 21, 2005
By Stuart Squatriglia

$2 million project to analyze the diminution of delta smelt; The sharp drop-off indicates a decline in estuary's health
San Francisco Chronicle 6/21/05
By Chuck Squatriglia, staff writer

The number of delta smelt and other species in the San Joaquin- Sacramento River Delta has dropped sharply, officials said Monday, and state and federal authorities have set aside $2 million to determine why.

The decline in the small fish -- which are at their lowest level ever - - is especially worrisome, scientists said Monday, because they were once among the most common fish in the delta and are a bellwether of the estuary's health.

"One reason there is such a high level of concern is because many biologists consider the delta smelt and their presence in the delta to be a pretty good overall indicator of the biological health of the delta," said Tina Swanson, senior scientist with the Bay Institute in Novato.

Researchers discovered the decline in January. Although they cannot say exactly how many smelt are in the delta, they know that the number of the fish pulled from the water -- called an abundance index -- during research ventures has reached an all-time low, Swanson said.

"While several of these declining species ... have shown evidence of long- term decline, there appears to have been a precipitous 'step-change' to very low abundance during 2002-2004," reads a scientific report on the issue.

Delta smelt are slender fish that typically grow 2 inches to 3 inches long. They have a blue sheen and appear to be translucent.

The declining numbers are seen among other once-common pelagic, or open water, fish, including the longfin smelt and threadfin shad.

"(The shad) was the most common fish you'd catch out there," Swanson said. Their decline is "extremely large, just a total crash."

Scientists believe there are several reasons for the decline, and experts from more than half a dozen state and federal agencies -- including the state and federal Fish and Game departments, the Environmental Protection Agency and the federal Bureau of Reclamation -- will spend the next several months analyzing existing data and gathering new information.

One suspected factor is the impact of drawing trillions of gallons of water from the delta each year to supply Southern California and the Central Valley, Swanson said. Changes in when and how much water is drawn have had a profound impact on delta wildlife, Swanson said.

Biologists are also concerned about the growth in once-clear delta sloughs and channels of nonnative species, including Egeria, a fast-growing weed.

The weed grows quickly, creating a perfect habitat for largemouth bass and other nonnative predators of delta smelt and other fish.

Rising numbers of striped bass and the Asian clam, which compete with the smelt and other small fish for food, also have hurt, she said.

Scientists also believe that increasing herbicide and pesticide runoff from upstream farms have polluted the delta.

"This is a very complex problem, and all of these causes are interrelated, " Swanson said. "It is not going to be easy to fix this, assuming we continue relying upon the delta for our water supply as we do."

Declining count of delta smelt

State authorities are alarmed by a dramatic drop in the number of delta smelt last year. The Smelt Abundance Index the number of fish pulled from the water during research ventures each year has dropped below the previous lows seen in the 1980s. Because of its sensitivity to a number of factors including changes in water flow and toxic chemicals, it is considered an indicator of the health of the Sacramento-San Joaquin River Delta.

Breeding season: From late winter to early summer. Fast growing, with majority of growth within the first 7 to 9 months of life.
Food: Small organisms called zooplankton
Life span: 1-2 years
Status: Threatened
Size: 2-3 inches, but can reach 5 inches
Habitat: Brackish waters in the Sacramento-San Joaquin River Delta
Odor: Smelt smell like cucumbers.
Source: California Department of Fish and Game
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/06/21/BAG7ADBRPL1.DTL&hw=water&sn=009&sc=778
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