The population of a little fish with an outsize influence on California's water supplies rebounded last month to its highest level in a decade, easing fears it was near extinction.

So few Delta smelt were turning up in recent years that biologists began worrying the population might have passed the point of no return. Even a good water year might not help, they feared, because with so few fish it might be difficult for them to find each other and reproduce.

That turned out not to be the case.

A wet winter and a long, cold spring were enough to boost a September index, the first of four fall surveys, to 50. Last year, the number was 6. In 2009, it was 1 and the year before 2.

"Add water, get fish," said Bruce Herbold, a fisheries biologist at the U.S. Environmental Protection Agency.
"We're not down to the level where they simply can't find each other to reproduce," Herbold added. "If it's a death spiral, it can be reversed, it looks like."

Overall, the improvement is an uptick, and not a sign that fish populations are necessarily on the road to health, biologists said.

"It's indicating that the capacity to rebound is still there if the conditions are good," said Carl Wilcox, Bay-Delta regional manager at the state Department of Fish and Game.

The bounce was mostly due to the weather, though it is possible new restrictions on water deliveries meant to protect smelt, salmon and other fish from extinction helped, biologists said.


While Mother Nature might get the credit, environmentalists said the lesson is that more water ought to pass through the estuary in years when rain and snow is not so abundant.

"This is a very clear indicator that flows matter to the health of the ecosystem," said Barry Nelson, a Natural Resources Defense Council water policy analyst.

Though the Delta smelt fan base is largely limited to the most ardent environmentalists and serious aquatic biologists, its status is considered a barometer of the health of an estuary that has been pressed by a loss of fresh water -- from both upstream dams and downstream pumps -- pollution and an army of invading insects, plants, jellyfish and fish.

Beginning about 2002, the number of Delta smelt and other small fish in the estuary's open water collapsed.
Because federal law requires the government to go to extraordinary lengths to prevent extinctions, sharp new regulations on water deliveries from Delta pumps were ordered to prevent smelt from going extinct.

Those new rules went into place at the same time a three-year drought began in 2007, and the result was less water for farms and cities, fewer fish and confusion about whether drought or environmental regulations were to blame for water shortages.

While the new rules received most of the blame, most of the shortages were actually due to the drought, according to state water officials' figures.

Meanwhile, agencies that saw their Delta water supplies threatened by the crisis pointed to other factors, especially pollution, for the estuary's troubles.

The September number is the first of four monthly measures that make up a key fall survey.

The numbers also were good for the other fish populations that collapsed beginning in 2002, including first-year striped bass, longfin smelt and threadfin shad, though the improvement for those fish was not as dramatic.