Critical index finds smelt nearly extinct in Sacramento Delta


Delta smelt have hovered close to extinction for years, but biologists say they’ve never seen anything like this spring.

“There’s nothing between them and extinction, as far as I can tell,” said Peter Moyle, a UC Davis biologist who has studied smelt and other Sacramento-San Joaquin Delta fish species for nearly four decades.

Delta smelt abundance graphLast week, the state Department of Fish and Wildlife released the results of spring trawling surveys that track adult Delta smelt. The surveys found just handfuls of fish across the huge area where they are known to spawn. The low catches were a marked drop from even the record low numbers of Delta smelt tallied in 2015’s trawls.

Steve Martarano, a spokesman for the U.S. Fish and Wildlife Service, said the index is used in part to help biologists estimate the entire population of the fish in the Delta.

Since the surveys began in 2002, the highest the Delta smelt population has ever been is about 600,000. Last year, the federal government estimated there were around 112,000. This year, biologists say there are likely just 13,000 fish, Martarano said.

“That’s alarmingly small for a fish that only lives for a year in a body of water as large as the Bay Delta,” he said.

Moyle said he remembers when he first started doing fish research in the Delta nearly four decades ago, and the smelt were among the most numerous fish species, numbering in the millions. He said that the low numbers now mean any sudden change to the smelt’s habitat – such as a sudden shift in water quality from a small pesticide spill – could kill off the entire population.

“It’s the indication that we’ve totally failed in our ability to manage Delta smelt to keep them from extinction,” Moyle said.

The Delta smelt, widely viewed as a bellwether species indicative of the estuary’s overall health, are an ongoing flashpoint in California’s water wars. In recent weeks, the fish has also taken on symbolic importance in the national political debate.

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