News

For immediate release: 7/17/06

GRDA confirms zebra mussels in Grand Lake

Grand Lake — The Grand River Dam Authority Office of Ecosystems Management confirmed on Thursday (July 13) that an adult zebra mussel was found in the waters of Grand Lake. According to GRDA Ecosystems Superintendent Dr. Darrell Townsend, Ph.D., the mussel was discovered in Ketchum Cove by a local fisherman, and because of other evidence that may point to reproduction, the mussels may be spreading.

“We believe we've found veligers this time,” said Townsend, “If so, that is evidence that these zebra mussels are reproducing.” According to Townsend, veligers are the microscopic free-swimming form of zebra mussel and their detection is likely an early warning sign of what's in store for Grand Lake. "We've taken photos and are sharing our results with other statewide experts for confirmation," said Townsend. "We want to be certain of what we have, because any bi-valve veliger shows similar characteristics. So we've collected specimens and will try to have other experts help us confirm what we've found."

The GRDA Ecosystems Department began monitoring the lake for the mussels following a previous sighting in February 2005 at the Disney State Park boat ramp. One adult mussel was also found at that time, but there was no evidence of reproduction. Since then, monitoring of that location has never led to any more sightings. “Unfortunately, this recent veliger evidence could mean the mussels have already established a pretty good hold,” said Townsend.

No successful methods for eradicating the mussels in the natural environment have ever been developed. And their history in other bodies of water has proven that containing them can be a steep uphill battle. In fact, the United States Fish and Wildlife Service has dubbed the small mussels with the “D” shaped shell and dark and light stripes (hence the name) “public enemy number one” on the aquatic nuisance species list.

The history—and the problem—of the mussel’s North America “invasion” have been well documented. They traveled across the Atlantic Ocean attached to the hulls of ships coming from Eastern Europe. In the late 1980s they were discovered in the Great Lakes and since then, they have spread down the Mississippi River, causing expensive problems wherever they go. Industries and municipalities along mussel-infested waterways in the Great Lakes region spend millions annually trying to contain them.

The Zebra Mussel Problem
What makes a small, seemingly harmless mollusk such a nuisance? According to Townsend, there are plenty of reasons.

“When you introduce an invasive, non-indigenous species like a zebra mussel into a new environment, it can cause a lot of problems,” he said. “Given the fact that they can reproduce very rapidly, they not only impose a serious threat to biodiversity, but they can have serious management implications for recreation and power generation alike.”

In fact, “it’s possible for them to reproduce one million offspring in a season,” said Everett Laney, fisheries biologist with the United States Army Corps of Engineers. In the late 1990s and again in the summer of 2003, Laney was the key presenter at a series of public meetings held to inform Grand Lake area residents about the zebra mussel threat.

The Oklahoma Zebra Mussel Task Force, established in the early 1990s, has tracked the Oklahoma mussel invasion which includes confirmed sightings in the McCllelan-Kerr Navigation System, Oologah Lake and, now, Grand Lake. “And once they arrive, they are there to stay,” said Laney, during his seminars. “You really can’t eradicate them. You just try to control them.”

Yet even as biologists look for methods to control them, the zebra mussels continue to be full of surprise. Originally, the mussels were thought to be a cold water species. Researchers believed they would spawn a couple of times a season, but when the water got over 80 degrees, they would get stressed and only be able to survive a few days. In fact, it was believed spraying heated water onto the mussels would be an effective method for eradication. However, since their arrival in Oklahoma, the mussels have adapted. Researchers now know they will spawn in warm water, even surviving in water over 90 degrees for several weeks. Also, it was once believed the mussels grew at a rate of one centimeter per year, and thus, their size was a good way to determine their age. However, later research has shown they can grow by one centimeter per month in the nutrient-rich waters of Oklahoma.

The mussels thrive in nutrient-rich waters because they are filter feeders, and each adult mussel can filter a liter of water per day. As they do this, they remove almost every microscopic aquatic plant (phytoplankton or algae) and animal (zooplankton), leaving behind clear, but nutrient-poor water, causing problems for other species.

“As they filter the water, they disrupt the food chain by redirecting energy flow,” said Townsend. “They can compete for food with some freshwater fish species, potentially disrupting growth and survival of many game species.”

Recognizing the threat
However, there are steps that can be taken to help hinder there spread across the water “and it’s in the best interest of all Grand Lake residents and visitors to follow these steps,” said Dr. Townsend. “Hundreds of boats are going in and out of Grand Lake all the time, so cooperation is an essential part of our efforts to try to keep this infestation in check.”

Adult mussels may attach to hard surfaces, and the young larval form of the zebra mussel, called veligers, may be transported in water. Veligers — about the size of the period at the end of this sentence — may be able to survive in any residual water. This is why preventing the transport of water in the bilge or live-well of boats is critical to stopping the spread of zebra mussels. Boaters who frequent known zebra mussel waters should be especially cautious. The mussels attach themselves to, and grow within, water intakes of both inboard and outboard motors and the subsequent restriction of water flow can cause motors to overheat.

Two years ago, GRDA worked in close cooperation with the United States Coast Guard Auxiliary Flotilla Commander, to erect zebra mussel warning signs at many public boat ramps to increase awareness and to help prevent further spread of this noxious invader.

Here are some steps you should keep in mind to help hinder the mussels spread:

• Boats should not be left in the water for extended periods of time. With regular use, engine heat should keep mussels from colonizing inside most engine parts.

• Always drain the bilge water, live wells and bait buckets.

• Inspect the boat and trailer immediately upon leaving the water.

• Scrape off any mussel found. DO NOT return them to the water.

• If possible, dry the boat and trailer for at least a week before entering another waterway. (If conditions are right, mussels can live for up to seven days on a boat hull outside the water.)

• Wash boat parts and accessories that contact the water using hot water (at least 140 degrees Fahrenheit), a ten percent solution of household chlorine bleach, or hot saltwater solution. Do not wash the boat at the ramp where these solutions could pollute the water. Always finish with a clean water rinse.

For more information on zebra mussels, or to report a possible sighting, contact the GRDA Office of Ecosystems Management at (918) 782-3382, or visit the GRDA Office of Ecosystems Management page on www.grda.com.

Veligers: From this microscopic view point, they may not look like much, but it is possible that these tiny "veligers" are zebra mussels, also known “public enemy number one” United States Fish and Wildlife Services aquatic nuisance species list. GRDA pulled the samples from the waters of Grand Lake's Ketchum Cove, near a location where a sighting of adult zebra mussels was confirmed in mid July. These veliger samples were sent to other statewide experts for confirmation.

ZMBuoy: Buoys like this one, marking zebra mussel monitoring sights, were placed on Grand Lake in 2005, after a zebra mussel was found at the Disney State Park boat ramp. The GRDA Ecosystems Management Department continues to monitor the lake for the presence of the mussels.