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Damaging exotic mussels in area lake are impossible to eradicate

Mike Bennett first visited Lake Piru in Ventura County as a kid with his grandparents. He’s continued to come back to it for his whole life. Since retiring from the Los Angeles City Fire Department two years ago, he’s had a lot more time to come out fishing on his boat.

Recently, Bennett was cleaning four large-mouth bass he’d caught. And he may have unknowingly caught another lake organism – one that wouldn’t be as auspicious a haul. Lake managers recently confirmed the presence of a damaging invasive species of freshwater mussel, called the quagga.

Quagga mussels are native to the Ukraine, but came to the U.S. on commercial ships, possibly in ballast water tanks or on ships’ anchors. The organisms flourished in the Great Lakes, where they have no natural predators. They have since spread throughout the country. Quaggas were discovered in the Colorado River in 2007 and shortly afterwards, in Southern California

The mussels are now known to exist in 26 lakes in Southern California. Lake Piru is the first lake not fed by the Colorado River to get the species.  

Living with a nuisance

The quagga is a filter-feeding bivalve mollusk that reproduces in high numbers, attaching to and eventually covering hard surfaces. Young quaggas float as microscopic entities known as villagers. They can attach to boats and then transfer to new bodies of water. 

A pair of adult quagga mussels can produce up to a million offspring. Scientists say that their high productivity and small size make them practically impossible to eradicate.

“Mostly we control them by preventing them from their spread. So we’re asking boaters to make sure that their equipment and everything in their water vessel – anything that’s been in the water – is clean, drained and dry before they go to uninfested water,” said Eloise Tavares, an environmental scientist with the California Department of Fish and Wildlife.

Making sure that incoming boats are completely dry is the only way to prevent the mussels’ spread. Officials at the water district that manages the lake said that they had strict boat inspection protocols in place for years.

“We’ve tried to prevent it. We’ve taken all these preventative measures to avoid it, said Mike Solomon, general manager of United Water Conservation District. “We were just very disappointed that they got through.”

Solomon said that now that the mussels are in the lake, it’s a matter of keeping their numbers in check. Lake Piru acts as a reservoir, replenishing groundwater for 340,000 residents downstream. Solomon said the district is acting quickly to establish a management program to control them.

“People should not look at this as a panic or a plague. It’s a problem that we’re going to deal with, try to resolve. But we’re acting very responsible. It’s something that we’re taking very serious. We’ve got the best people we can on it, and we’ll resolve it, but it’s still real early in the game. It’s going to take awhile,” Solomon said.

An expensive problem

Solomon said there is no chance that the mussels would grow to a point that they would choke off water supplies to residents and farmers that rely on them. He said that the water district would clean off accumulated growth regularly.

That kind of program can be costly and time consuming. An official for the Metropolitan Water District said it spends three-to-five million dollars a year controlling quaggas.

“We clean it once, twice a year. We go down with divers. We visually inspect it. If it appears to be getting clogged, then we’ll send divers down, and they will literally jetwash it and clean it manually,” said Jim Green, water systems operations manager for MWD.

The United Water Conservation District’s operations are much smaller than MWD’s, so its quagga costs will be far less. Solomon said costs will be paid using pump charges and property tax money the district receives. However, he said he doesn’t know what the cost will end up being. The water district is waiting for scientists to report on how extensive the infestation is.

“We’re putting together a plan that’s required by the state -- how we’ll deal with it and try to resolve it. So the cost will depend on what plan we put in place,” Solomon said.

Early on in the process

Just a few hundred yards away from where Bennett was fileting his day’s catch, a ranger was down on the lake, pulling up one of six devices that monitors the quaggas’ growth. He pointed to a small, lone quagga, nestled in a groove on the device.

“Populations are present but at low densities, meaning they’re not colonizing. They’re not clustering. They are present, but we’re not seeing them in big numbers, which is a good thing,” said Clayton Strahan, senior park services officer at Lake Piru.

Strahan said he and his colleagues are receiving a lot of training and information from state agencies about how to cope with the presence of quagga mussels. Since the mussels were discovered, they’ve increased monitoring and education for visitors to the lake. Apart from that, Strahan said he’s not yet clear on how his daily routine will change.

“We’re still in the early discovery phase, so knowing exactly what impacts it’ll have on our operations – we’re not there yet.

As for boaters, it means having to decide how they’ll spend time on Lake Piru. Other area lakes that are leery of getting infested with the exotic species will likely require extensive dry quarantine periods for boats coming from Lake Piru.

Mike Bennett said he’s not overly concerned about the recent discovery of quaggas. Their presence in the lake isn’t likely to change his fishing plans.

"It doesn’t affect mine, because I’m mainly on Piru, and if I go to another lake, I’m usually in someone else’s boat,” he said.