Steelhead Trout Decline Still Mystifies Fish Experts

BY BILL KOENEKER

Scientists are still puzzling over the sudden decline of the steelhead population in Malibu Creek this summer, but may be closing in on an answer, while research and study continues.
Rosi Dagit, a senior conservation biologist for the Resource Conservation District of the Santa Monica Mountains, said that a plan of action was agreed upon at a technical advisory meeting two weeks ago and the study is continuing based on the recommendation of a group of researchers and scientists.
“We agreed to collect samples, collect carcasses to be shipped off to a lab, to continue to monitor the water quality,” she said.
Any attempts to explain the die-off of the protected species and all other underwater critters are complicated because it must include an explanation for all other fish species that also suffered dieback, including crayfish, considered a very hearty species.
“We have ruled out chemical pollutants because of the toxicology tests we conducted,” Dagit said.
To add to the complex and complicated scenario, the die-off only took place in a certain section of the creek “There is no die-off above the Rindge Dam,” she added.
Scientists began looking at the low dissolved oxygen in the water and the high water temperatures. “There is also a high percentage of the growth of algae. We don’t and won’t have some of those test results back until October,” Dagit said.
Dagit and her colleagues are currently collecting algae samples because of a current theory concerning the algae.
She said the decomposing algae contain what are called halogens, what she called a “suite of chlorine components.”
The biologist said the algae release the chlorine compounds in the water. “That is a real problem for anything living in the water,” she said.
Dagit said the National Marine Fisheries Service has arranged for the algae samples to be sent off to a lab. “We are taking samples from three locations for three weeks to see if it is the problem,” she said.
The crayfish carcasses are being sent off to another lab in Sacramento.
The past year’s decline, recalled Dagit, is much like the die-off in 2006. Besides the steelhead, the heartier populations also died off, including catfish, carp, crayfish and others.
By 2008, there were 1300 trout in the creek. There are less than 250 today, according to Dagit, who indicated there is no extensive data for die-off in 2006 to draw any conclusions.
That makes efforts this year all the more important. “It has been pretty impressive how the scientific community and water quality folks have come together. They have been very helpful and offered a cooperative effort,” Dagit added.