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Smelt Ups and Downs

It should have been a good year for both Delta and longfin smelt, what with increased freshwater inflows, an ideal entrapment zone location in Suisun Bay, careful water project management for salmon and smelt protection, and the state's short-lived but fish-friendly 1630 water rights decision. "You'd expect, if you were a Delta smelt, that this is the best you're going to get," says Dale Sweetnam of Cal Fish & Game.

But Sweetnam didn't see the kind of numbers he expected in the summer townet index. It wasn't until the fall midwater trawls that he stopped worrying. September produced an index of 374.6 and October, 470 - a sizable jump up from the 71.5 and 3.5 observed in the same months last year. The longfin, on the other hand, improved over 1991-1992 indexes but "fell far short of what was predicted for 1993," according to Fish & Game's Randy Baxter.

Historically, the relationship between flows and abundance has been different for each species. The Delta smelt seem to do better with medium, rather than high and low flows. The longfin, according to an analysis of 1967-1992 data by Baxter, seem to increase with flows in a more linear fashion. "The argument for longfin has always been add a little water and the longfin will bounce right back," says Baxter. "But this year, they didn't bounce as high as we expected. Perhaps there weren't enough spawners to take advantage of the flows."

Meanwhile, EPA's Bruce Herbold recently added a little salt to the flows/abundance equation by looking back over the past 25 years for correlations between the location of the 2 ppt isohaline (parts per thousand salt in the water) in the Estuary and Delta smelt abundance. Herbold wanted to see if the criteria his agency is proposing for a new Delta salinity standard protected the smelt. They did. Over the past quarter century, the more days the 2 ppt isohaline occurred in Suisun Bay, the more smelt. Herbold also discovered that the peak of the positive correlation occurred between Roe Island and Middle Ground - just where EPA plans to suggest a water quality standard monitoring station.

Contact: Dale Sweetnam and Randy Baxter (209)948-7800; Bruce Herbold (415)744-1992

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