Mention the word carp and you will get a variety of responses. In Europe, the carp is a sought after fish both for food and for sport, and in the United Kingdom there is even a huge carp angling market. Izaak Walton once said this about the carp. "The Carp is the queen of rivers; a stately, a good and a very subtil fish."
Mention the word carp in this country and you will get a mix of responses. For the most part, though, the carp is classified as a rough fish, an unwanted exotic that has become known as an invasive species that can destroy the water quality of shallow water lakes and rivers reducing the populations of desired game fish.
Talk about two completely opposite views. Revered in one world and hated in another.
The carp was introduced in this country in the late 1800s and quickly spread across North America. It has become a real problem in the Midwest, where there are thousands of shallow water lakes. It is in these shallow water lakes that the common carp has caused extreme damage to the water quality, the aquatic vegetation and the sought after game fish.
Because, you see, carp abound in these shallow water lakes.
So, what's being done? I contacted Mike Hawkins, Fisheries Management Biologist, because I knew he and several other biologists here in northwest Iowa have been working on revitalizing shallow water lakes through a shallow water lake management program.
According to Hawkins, until recently, very few studies have been done on carp. "We've done all kinds of studies on game fish, because that's what people are interested in. Now, we're realizing as we start rejuvenating these shallow water lakes, that the common carp is one of the reasons for the declines in these bodies of water. As a result, we need to learn more about the carp if we are to have any chance of controlling them."
Peter W. Sorensen, Professor in the Department of Fisheries, Wildlife, and Conservation Biology at the University of Minnesota, has put together a study on carp that really shines a light on their habits and ways to control them.
For years, commercial fishermen have seined lakes for rough fish, the most prevalent being the common carp.
According to Hawkins, he has contracts with commercial fishermen for all of the lakes here in northwest Iowa. They will take thousands of pounds of rough fish out each year, but the pounds of carp per acre remains pretty much the same.
Take carp out of a lake and the ones that remain grow and produce offspring to fill the void created. "In fact, the commercial program in Iowa was not designed to reduce carp numbers. Decades of state sponsored removal efforts well into the mid 1900s showed that large scale removal efforts were not effective at reducing the population.
In fact, it has been widely believed that such efforts actually triggered carp reproduction events," notes Hawkins.
That is until Sorensen's study. "From his study, we see that the key is targeting and controlling very specific areas of spawning habitat.
Generally, this critical spawning habitat is found in isolated sloughs or wetlands that are permanently or periodically connected to the lake.
In Sorensen's study, there is evidence suggesting that carp successfully reproduce only after winter kills events in these connected marshes. Keeping adult fish from entering this habitat is key to controlling the population. Removing adult fish is only one part of the puzzle."
So, that is the approach Hawkins and his staff are now using. Structures are being planned on some lakes that will stop the movement of adult carp into the connecting sloughs. "They will still go through spawning activity in the main lake, but there is very little protection there for the eggs and the newly-hatched fry."
In other words, the young of the year carp make a great meal for the other species of fish in the main lake.
It is hoped that controlling carp populations will have a positive impact not only on a lake's fishery, but also its water quality and habitat. Invasive carp populations have a significant impact on the turbidity of the water, algae blooms, and the lack of aquatic vegetation.
Combining this new research with better technologies for preventing fish movement may lead to more manageable populations of carp and healthier lakes