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From the Iowa DNR:
DNR Working to Improve Walleye Fishing at Rathbun
MORAVIA, Iowa - The annual spring walleye egg collection at Lake Rathbun ended two weeks ago and the conditions could not have been better. Fisheries crews with the Iowa Department of Natural Resources collected adult walleyes for nine nights to supply the hatchery with enough eggs to produce 51 million walleye fry.
The bulk of those adult walleyes can be traced to the 2006 year class. Walleyes are an important resource at Lake Rathbun and their popularity continues to grow.
"While we caught a lot of fish, this 2006 year class could be so much larger," said Mark Flammang, fisheries biologist for the DNR at Lake Rathbun. "Our walleye population is down, but the weather was perfect and that attracted a lot of fish to the dam."
Walleyes have not always been as prominent in the lake as they are today. In the 1980s, the population crashed. A major effort to increase walleye survival in the 1990s re-established the population and the lake began its run as a major player in the Midwest walleye fishing world.
Then, the 2000s brought four years of flooding that knocked the walleye population back down.
Rathbun Flood Control Reservoir
The U.S. Army Corps of Engineers is in charge of Lake Rathbun's water level and operates the lake as a federal flood control reservoir. When water level rises, the Corps will increase the water release to get the reservoir to normal pool in case it needs to store water to prevent downstream flooding.
In 2001, Rathbun experienced flood conditions from late winter on through summer and the Corps allowed as much water as possible to pass through the dam. Mixed in with the out-flowing water was an estimated 40 percent of the adult walleye population. Other high water years in 2007, 2008 and 2009, also impacted the population, but were not as bad.
"The walleye loss is not just during flood events in the spring, its high flows anytime," Flammang said. To try to quantify the loss, he collected walleyes below the spillway from October 2009 to February, tagged them and retuned them to the lake. Of the fish tagged, 10 percent were recaptured below the spillway, during moderate flows, when high numbers of walleyes would not normally be near the dam.
The problem is magnified in the spring when the outflows are high and the walleyes are moving to the dam looking to spawn. Many are washed through and end up in the Chariton River. Since the Chariton River does not have the characteristics of a walleye stream, they move south to Missouri eventually ending up in the Missouri River.
"We need to find an answer to minimize walleye loss," Flammang said. "There is a possible solution. The first step to solving this problem is to reduce the outflow at a time when walleye abundance is critical and outmigration peaks, which is during the spring because most of the spawning habitat is at the dam, and then install a non-physical barrier to keep the fish away from the outflow area and in the lake."
Flammang said there are non-physical barriers in place today around the country that use strobe lights, bubbles and other techniques to keep fish away from specific areas.
The non-physical barrier has the potential to help walleyes and to improve fishing across the board, including the crappie and white bass. Rathbun has a huge crappie class coming up and the population looks to be strong for years to come. White bass numbers could also improve.
"There is a lot of good that can come from this," Flammang said. "I hope to get to a point to find a deterrent system."
Based on his five month study, the impact of the lost walleyes is $200,000 in fishing and the local economic benefit. "If we can reduce our loss to 30 percent of what is currently is, the investment in the barrier can be recouped rather quickly," he said.
But until then, Flammang will continue to capture walleyes that wash through the dam, tag them and return them to the lake. He has tagged about 1,300 walleyes so far and has roughly 500 tags left.
"There will be good fishing here for walleyes, crappies, channel catfish and white bass," Flammang said. "This lake is the most important walleye fishery south of I-80. If we could get the barrier, we could take the walleye population to new heights and protect other species as well."
And Lake Rathbun would again be mentioned among the premier walleye and crappie fisheries in the Midwest.
From the Iowa DNR:
DNR Working to Improve Walleye Fishing at Rathbun
MORAVIA, Iowa - The annual spring walleye egg collection at Lake Rathbun ended two weeks ago and the conditions could not have been better. Fisheries crews with the Iowa Department of Natural Resources collected adult walleyes for nine nights to supply the hatchery with enough eggs to produce 51 million walleye fry.
The bulk of those adult walleyes can be traced to the 2006 year class. Walleyes are an important resource at Lake Rathbun and their popularity continues to grow.
"While we caught a lot of fish, this 2006 year class could be so much larger," said Mark Flammang, fisheries biologist for the DNR at Lake Rathbun. "Our walleye population is down, but the weather was perfect and that attracted a lot of fish to the dam."
Walleyes have not always been as prominent in the lake as they are today. In the 1980s, the population crashed. A major effort to increase walleye survival in the 1990s re-established the population and the lake began its run as a major player in the Midwest walleye fishing world.
Then, the 2000s brought four years of flooding that knocked the walleye population back down.
Rathbun Flood Control Reservoir
The U.S. Army Corps of Engineers is in charge of Lake Rathbun's water level and operates the lake as a federal flood control reservoir. When water level rises, the Corps will increase the water release to get the reservoir to normal pool in case it needs to store water to prevent downstream flooding.
In 2001, Rathbun experienced flood conditions from late winter on through summer and the Corps allowed as much water as possible to pass through the dam. Mixed in with the out-flowing water was an estimated 40 percent of the adult walleye population. Other high water years in 2007, 2008 and 2009, also impacted the population, but were not as bad.
"The walleye loss is not just during flood events in the spring, its high flows anytime," Flammang said. To try to quantify the loss, he collected walleyes below the spillway from October 2009 to February, tagged them and retuned them to the lake. Of the fish tagged, 10 percent were recaptured below the spillway, during moderate flows, when high numbers of walleyes would not normally be near the dam.
The problem is magnified in the spring when the outflows are high and the walleyes are moving to the dam looking to spawn. Many are washed through and end up in the Chariton River. Since the Chariton River does not have the characteristics of a walleye stream, they move south to Missouri eventually ending up in the Missouri River.
"We need to find an answer to minimize walleye loss," Flammang said. "There is a possible solution. The first step to solving this problem is to reduce the outflow at a time when walleye abundance is critical and outmigration peaks, which is during the spring because most of the spawning habitat is at the dam, and then install a non-physical barrier to keep the fish away from the outflow area and in the lake."
Flammang said there are non-physical barriers in place today around the country that use strobe lights, bubbles and other techniques to keep fish away from specific areas.
The non-physical barrier has the potential to help walleyes and to improve fishing across the board, including the crappie and white bass. Rathbun has a huge crappie class coming up and the population looks to be strong for years to come. White bass numbers could also improve.
"There is a lot of good that can come from this," Flammang said. "I hope to get to a point to find a deterrent system."
Based on his five month study, the impact of the lost walleyes is $200,000 in fishing and the local economic benefit. "If we can reduce our loss to 30 percent of what is currently is, the investment in the barrier can be recouped rather quickly," he said.
But until then, Flammang will continue to capture walleyes that wash through the dam, tag them and return them to the lake. He has tagged about 1,300 walleyes so far and has roughly 500 tags left.
"There will be good fishing here for walleyes, crappies, channel catfish and white bass," Flammang said. "This lake is the most important walleye fishery south of I-80. If we could get the barrier, we could take the walleye population to new heights and protect other species as well."
And Lake Rathbun would again be mentioned among the premier walleye and crappie fisheries in the Midwest.