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Fish Hatcheries take Precautions to Prevent Spread of Zebra Mussels during Walleye Spawn
Posted: 04/11/2013
The discovery of zebra mussels in East Okoboji and Upper Gar lakes is changing the way the Iowa Department of Natural Resources operates its successful walleye collection and spawning effort to reduce the potential of spreading the aggressive aquatic invader to other waters.

Zebra mussels are well established in the Mississippi River and have become part of the fabric of Clear Lake. Small juvenile zebra mussels, called veligers, have been found in Lake Rathbun. Once established, there is no way short of draining the lake to eliminate zebra mussels.

Zebra mussels are often introduced to new areas in bilge water, or attached to boats, trailers, waterfowl decoys and fishing equipment. To prevent spreading zebra mussels and meet the expectations of Iowa anglers, fisheries staff will use filtered water or water from non-infested sources to transport eggs, fry and fingerlings.

Fisheries crews began netting at Lake Rathbun last weekend and at East Okoboji and Storm Lake on Monday. Clear Lake, West Okoboji and Spirit Lake will be netted last.

While zebra mussels have not been found in Spirit Lake, for the purposes of the hatchery, the DNR is treating it as if it is infested.

Fisheries crews will try an experimental method, called dry stripping, where eggs are collected from one lake where zebra mussels are present, then transported without water to a mussel free location where they are fertilized and incubated.

The DNR has set up incubation batteries at Storm Lake and Guttenberg to hatch fish for locations without zebra mussels. Storm Lake is zebra mussel free, and Guttenberg will use well water then discharge into the Mississippi River.

This dry stripping method has been used in Kansas and Ohio, with varying degrees of success.

“We are not sure if dry stripping is going to work, but are going to err on the side of caution,” said Joe Larscheid, chief of the Iowa Department of Natural Resources Fisheries Bureau.

He said dry stripping requires a staff member to collect a walleye from the holding tank, dry it off and pass it to another who will spawn the fish. The idea is to keep one step between the tank and spawning to reduce the potential of a veliger hitching a ride.

“Our stocking plans include similar numbers of walleyes as we have produced in the past, but with additional steps because we don’t want to spread zebra mussels,” Larscheid said.

Walleye stocking requests are for 125 million fry, 640,000 2-inch fingerlings, and 300,000 5 to 8-inch advanced fingerlings.

Summer Visitors

These lakes host tens of thousands of boaters each weekend in the summer that will need to stay vigilant to not bring zebra mussels to new lakes or streams.
Kim Bogenschutz, who coordinates the aquatic invasive species (AIS) program for the DNR, will begin looking for veligers in the Iowa Great Lakes shortly after ice out.

“We will sample each lake at multiple locations collecting water samples as soon as gillnets drop, using sampling plates and collecting rock samples in August and September,” she said. “Veligers are at peak numbers in July and August; the same as boating traffic at these lakes.  My concern is this is another spot where zebra mussels can spread from. Zebra mussels were found last summer at Bluebill Lake, which is near Clear Lake.”

Bogenschutz said her focus will be to explain to boaters how to properly inspect their watercraft, trailer and equipment to remove any visible plant animals or mud; drain water from the boat, motor, live well, and bilge; and dispose of unwanted bait in the trash all before leaving the water body. 

She said veligers are comparable in size to the width of a human hair and not possible to see in the water so it’s important to rinse or dry the boat, trailer and fishing equipment to remove or kill species that are not visible. Before going to another water body, rinse with high pressure and or hot water or dry it for at least five days.

“We will have eight staff covering the Iowa Great Lakes at boat ramps beginning in middle May to hand out information and explain how to clean watercraft,” she said.  “This will change the way people boat at the Iowa Great Lakes.”

Zebra mussels are in focus because they are changing the way Iowa will produce walleyes, but there are additional invaders causing problems across the state.

Asian carp, Eurasian watermilfoil, brittle naiad and other exotic species are crowding out native species and threatening Iowa lakes and streams.