Studies continue into summer as district looks to rid reservoir
of invasive pests
Doubts about the effectiveness of measures designed to kill
invasive zebra mussels in the closed-to-the-public San Justo
Reservoir will force a repeat of an eradication study this
summer.
Studies continue into summer as district looks to rid reservoir of invasive pests
Doubts about the effectiveness of measures designed to kill invasive zebra mussels in the closed-to-the-public San Justo Reservoir will force a repeat of an eradication study this summer.
The popular fishing and boating spot off Union Road has been off limits to recreational users since the fingernail-sized mussels were discovered there in January 2008. The San Benito County Water District continues to use San Justo to store and distribute water for agricultural use, but the gates have been closed and locked for more than two years.
The United States Bureau of Reclamation this week met with Jeff Cattaneo, the water district’s executive director, to discuss the status of a pilot study that evaluated how effective exposing the mussels to the elements would be in their eradication.
“The study had some questions that remained,” Cattaneo said. “It appears it is very effective but we are looking for whether it’s going to be 100 percent effective or not. In order for us to use it as part of the eradication effort, we need to be relatively assured of its effectiveness.”
First conducted during the cooler and more humid winter months, the study revealed that the lives of many mussels were extended by the more temperate weather, with some living up to 40 days out of water.
“There was some uncertainty at the end of that time whether those mussels were still alive or dead,” Cattaneo said. “We’ll repeat the full study in the summer when the ambient conditions will be significantly different,” with warmer temperatures and lower humidity. “If it appears that it cuts down on the time the mussels need to be exposed to air, and it looks to be near 100 percent effective, we’ll incorporate that into the eradication plan.”
Zebra mussels originated in Europe and were found in the eastern United States in the 1980s. The freshwater creatures are harmful to water systems because they produce toxins that kill native organisms and also reproduce so quickly and in such great numbers that they can clog drinking water or agricultural irrigation delivery systems.
Researchers put some mussels on shore in baskets that look like butterfly nets to simulate the conditions of having the reservoir drawn down. They were evaluated at 10, 20, 30 and 40 days to see if they remained alive or not.
The water district has kept the water elevation down in San Justo as it awaited word on whether the exposure study would need to continue.
“Drawing down the reservoir eliminated a significant portion of the population, so we will try to expand on that this summer to try to minimize the population,” Cattaneo said.
Another mussel eradication idea has been to treat the mussels with potash, or potassium chloride, a type of salt that disrupts the creatures’ ability to filter feed. Officials believe the potash would force the mussels to open up, at which time they could be killed with chlorine or left to die on their own.
Water district officials want to be certain that any course of treatment is nearly foolproof.
“If the results from the study indicated there’s still some uncertainty about effectiveness or they’re inconclusive, we have to evaluate how much risk we want to take in the eradication,” Cattaneo said, noting that it will take “several million dollars” to complete the process.
Even though San Justo remains drawn down, the water district has enough water to deliver to its customers during the summer.
“Because of reduced allocations (from state water sources) we’ve experienced demand that hasn’t been as extreme as it could be,” Cattaneo said.
Until an eradication plan is decided upon, the reservoir will remain closed to the public.
“Nobody is saying right now that we should open it back up until we determine whether the eradication process is going to be effective,” Cattaneo said. “Everybody’s really concerned about mussels being transported out of San Justo into other water bodies in California. The Santa Clara Valley Water District, which is the closest district with reservoirs, is very concerned what would happen to their reservoirs if fisherman were to inadvertently transport the mussels into those waterways.”
Cattaneo said he expects to meet with the Bureau of Reclamation within the next week or two to discuss the next steps in the eradication study.
