Two fish traps using large rotating drums to funnel fish into holding tanks have been lowered into the Russian River near Forestville for the annual chinook salmon survey that began Wednesday.
The decadelong survey is the only count of chinook smolt in a California coastal stream, and it has uncovered a healthy population in the Russian River that no one believed existed, said Sonoma County Water Agency biologists.
?We really wouldn?t have known about the chinook presence in the Russian River. The original intent was to collect information on steelhead and coho,? said Dave Manning, a biologist and senior environmental specialist for the Water Agency.
Chinook, as well as coho salmon, are on the federal endangered list.
?We found that there is this self-sustaining population of chinook, they are the largest component of the fishery in the Russian River ? and that came as a surprise to many people,? Manning said.
The fish traps are mounted on pontoons and were lifted into the Russian River just downstream of Wohler Bridge on Tuesday.
The drums turn slowly in the river?s current, churning the dark green water and drawing the small fish into holding tanks.
Each day, biologists will empty the tanks to measure and identify the fish. Some will have a fin clipped and then be released upstream to see if they are caught again.
The fish that are scooped up are usually two to three inches and migrating to the ocean, providing an indication of the number of adults that had traveled up the river months earlier to spawn.
Biologists, who said the migration season is just getting started, found a half dozen chinook, two small coho and a few hatchery-raised steelhead in the traps on Wednesday.
The smolt run will last until June, with the peak between mid-April and mid-May,
The traps will catch about 5 to 10 percent of the smolt migrating downstream, along with some 2-year-old steelhead that can be larger, up to 8 inches long.
From the number caught last year, it is estimated about 50,000 were headed to the ocean, compared with 225,000 in 2002, the highest count, and 125,000 in an average year.
?It is the lowest we had, but not that far off of the average for the last 10 years,? said Shawn Chase, a Water Agency biologist and senior environmental specialist.
Using underwater cameras and fish ladders, the Water Agency also counts the number of salmon and steelhead going upstream in the fall. Last year?s total of 1,125 was the lowest ever recorded.
Chase said the problem is that a decade of data is not enough to determine what is average.
?We have a nine-year look at how many chinook, but there is no way to put it into historical context of what it means,? Chase said.
You can reach Staff Writer Bob Norberg at 521-5206 or firstname.lastname@example.org.