What’s killing Malibu Creek’s steelhead
Twice in recent summers, Malibu Creek’s fledging population of endangered steelhead have been decimated, leaving the experts baffled and saddened. In 2006, hundreds of the fish turned yellow and died after a heat wave that was accompanied by a foul-smelling black layer of rotting algae and bacteria in the stream bed. The ooze earned a nickname: Malibu Muck. By early 2008, the population of juvenile steelhead managed to edge toward 3,000 again, giving biologists hope that the fish were making a strong comeback. But last year, the die-offs returned with a vengeance. Steelhead, as well as the hardy carp, crayfish and others, died en masse. The Malibu Muck was back, too. This time, the baby steelhead didn’t turn yellow but the population in the creek still plummeted from about 1,300 to just 200 young fish. In the bad years, “everything was dying,” says conservation biologist Rosi Dagit. “And we really had absolutely no clue why.”
Last week, Dagit and other conservation biologists waded into the creek to look for answers, launching the most comprehensive water quality study ever undertaken in the crucial Santa Monica Mountains watershed.
waist deep in Malibu Creek, Steve Williams and Kevin Jonz carefully
slid a high-tech measuring device called a sonde inside a plastic
housing and dipped it into the algae-green water. They anchored the
two-foot cylinder to the creek bed with a steel fence post and then
fastened the contraption to a willow thicket with a stout metal chain. In all, five sondes were installed—four in Malibu Creek and one in nearby Topanga Creek. The devices will gather six vital measures of water quality every 30 minutes, around the clock, from April to October. The thousands of data points on water temperature, clarity, pH, algae levels, conductivity and oxygen levels will provide scientists with a full view of the changes in water quality over an entire season, from the high flows of spring to the slack low water of late summer and fall.
Read the rest at Zev Yaroslavsky's blog.