The Delta smelt population, already sliding toward extinction, plunged to yet another record low this year.

The figures, made public Wednesday by the California Department of Fish and Game, show the key measure of the Delta smelt population _ a four-month fall survey index _ fell to 26 from its record low last year of 74.

"That's definitely got people's attention," said Chuck Armor, operations manager for the Fish and Game Department's Central Valley Bay-Delta branch.

The index is a measure of fish caught during trawls between September and December. It is considered the best indication of the relative health of Delta smelt, but cannot be used to predict the actual number of fish in the population.

Longfin smelt also continued their decline this year, while threadfin shad and young-of-the-year striped bass rebounded somewhat but remain far below population levels of several years ago.

The grim news comes as Delta smelt are beginning to move upstream to spawn in the dangerous territory near state and federal water pumping plants, which Wednesday were running full bore.

"The fish are moving up, we know they are moving upstream to spawn," said Bruce Herbold, a biologist at the U.S. Environmental Protection Agency.

Herbold, referring to figures that show water users received more water through those pumping plants last year than ever, said he was concerned that continued pumping could further damage the smelt population.

"Last year was a terrific year for the water exporters, and they're well on their way to doing that again this year," Herbold said. "I'm concerned."

Herbold said he has been trying to convince water operations managers to curtail pumping in recent weeks, so far to no avail.

"Up to now, we haven't seen any smelt (at the pumping plants)," said Jerry Johns, deputy director of the Department of Water Resources.

Johns said there are ongoing discussions about how pumping cutbacks will be enforced when and if Delta smelt start turning up at the pumps' fish salvage sites, adding that the high river flows could push the little fish downstream and away from the pumps.

"I think we got bailed out by the rain. This is going to be an interesting year to work through," he said.

The steep drop comes on top of decades of decline for Delta smelt, which were listed as a threatened species under the Endangered Species Act in 1993.

Beginning in 2002, populations of Delta smelt and several other open-water Delta fish species began plunging for unknown reasons. The latest results mean that for Delta smelt, the most imperiled of those fish species, the situation has gone from very bad to much worse.

"That's appalling but not surprising, given what we've been seeing earlier. It is definitely in danger of extinction at this point," said Tina Swanson, a senior scientist at the Bay Institute, an environmental research group.

Mike Taugher covers natural resources. Reach him at 925-943-8257 or mtaugher@cctimes.com.