Zebra mussel population in El Dorado Reservoir makes rapid increase

After three years of welcome declines the population of zebra mussels at El Dorado Reservoir  has grown exponentially this summer, according to Craig Johnson, Kansas Department of Wildlife, Parks and Tourism fisheries biologist for the lake.

He recently learned summer testing found 114 zebra mussel larvae per liter of lake water. Last year the figure was 4.5 per liter.

Difficult to find a few months ago, adult zebra mussels are again common at El Dorado Reservoir. Recent tests show larvae numbers have jumped from 4.5 to 114 per liter of lake water in the past year.

“I was kind of afraid that’s what would happen when we saw the increase in adult zebra mussels this summer,” Johnson said. “I’m not sure I was expecting this much of an increase, though.”

El Dorado was Kansas’ first lake infested with zebra mussels back in 2003. The population peaked at about 300 larvae, called veligers, per liter in 2006. Their numbers began a serious crash in 2007. The population reduction could have been caused by rapid water level fluctuations that had the lake change from six feet low to six feet above normal levels.

In 2008 El Dorado had 15 larvae per liter and 8 per liter in 2009.

Johnson said some of the past reduction may be attributed to high flow-through at the lake in 2009 and 2010. This year not much water has been released from the lake.

“(The population increase) may be partially because every veliger the adults made this year have stayed in the lake,” Johnson said. “We’ve had almost no outflow and obviously had enough adults left to produce a lot of veligers.”

Zebra mussels came to the Great Lakes region in the 1980s in the bilge water of ships coming from Europe. They’ve since spread to many states and cause problems by clogging intake structures at power and water plants. Some facilities spend up to $1 million per year battling zebra mussels.

They can also out-compete native wildlife for nutrients in the water. Such competition from a record number of zebra mussels may have contributed to a crash in El Dorado’s gizzard shad population in 2006. Shad are an important baitfish that provide food for such popular sportfish as bass, walleye, crappie and catfish.

Zebra mussels have sharp shells that can also cut the hands and feet of swimmers and waders.

Mike Miller, Wildlife and Parks information chief, said Kansas currently has zebra mussels in 14 lakes. Locally that includes Cheney, El Dorado, Marion Reservoirs. Marion’s population has also increased dramatically in the past year. Cheney has held some of Kansas’ highest densities in recent years.

Lake Afton and Winfield City Lake also have zebra mussels.

Miller and Johnson said Wildlife and Parks continues to urge lake-users to “Clean, Drain, Dry” all boats, bait buckets and other equipment that could carry infested water or zebra mussels from one body of water to another. For information on preventing the spread of aquatic nuisance species in Kansas go to www.kdwp.state.ks.us.

Johnson said he’s not sure what to expect next from El Dorado’s zebra mussel population. “We’re the first to do this, to jump back up this quick,” he said. “I don’t know if it’ll jump back up to 300 (per liter) like it did in 2006 or not. Your guess is as good as mine.”