Column: Ideas being tested to control carp population

Talk about it

WORTHINGTON — Last week, I shared my views about what I thought about the common carp and how it made its way into almost every body of water in North America.

Carp are here to stay and the only thing that can be done to limit their devastating effects is to try to control their numbers.

As I shared last week, these control measures are really like putting a band-aid on a severely bleeding artery. Even if you can successfully kill off an entire lake, these measures have a short time frame of success because fish do swim around. In high-water flows, fish can move right back into most lake and river systems and the cycle continues.

In the past, when a lake was reclaimed (killed off), it was then subsequently restocked with substantial numbers of large-species predator fish in order to control the offspring of any carp that might make it back into the system. These methods are changing as research continues to evolve in carp management. Researchers now are trying to find one or more weakness in the carp’s life cycle in order to exploit that weakness and gain the advantage in carp management.

Most anyone who spends time at the lake will have seen carp spawning in the shallows in midsummer. They thrash around, sometimes in large groups and can really cause a ruckus. Carp can lay close to a million eggs each.

Multiply one million by thousands of carp and one would think that the only fish that would be in a lake would be carp.

Carp numbers are pretty steady for the most part and their populations generally spike only when the body of water experiences a winterkill.

A winterkill (death of fish due to oxygen starvation in winter) reduces the number of predators that eat the carp eggs and the resulting offspring. Kill off the population control and carp numbers skyrocket.

Several ideas are being tested in order to achieve better results controlling carp. Having enough predator fish to eat the eggs and young seems to work the best. The problem with this method is that a carp can grow from a hatched egg to six inches in length in as little as six months.

Once these fish exceed six inches in length relying on predator fish doesn’t get the job done. Researchers are trying to find different ways to attract and catch adult carp and then remove them. If you can remove a large enough percentage of the adults then the predator fish can finish off those that do manage to hatch and survive.

Trapping these adult carp might include baiting them with food or better yet the release of pheromones that will attract carp to a certain area where they can be netted or trapped. Once the populations are reduced predator fish can do the rest. Some of the reasons that carp do survive as well as they do is that they will spawn almost anywhere. Many fish species need just the right kind of habitat to spawn successfully. Carp are the opposite.

They can use a wide variety of locations and are willing to swim into very shallow waters and streams to do so. Other fish don’t share this same willingness.

One other change that is coming to fruition is that when restocking is done after reclamation or other carp population reduction efforts, the subsequent stocking now uses different species of fish. In the past it was the large predator fish that were stocked. These larger species take longer to grow up and participate in carp control. One big change in the future will be to restock these lakes with smaller species and in much larger numbers than in the past. Perch and other pan fish by the thousands can eat more carp eggs and young of the year than hundreds of bigger fish can just based on the nature of the numbers. This change to more numbers and smaller species is a big shift from the efforts of the past.

Carp are here to stay and methods to control them will improve, but not with out time and large quantities of money. I for one want carp gone for good and will follow the research as it develops. When the passenger pigeon was wiped off the earth years ago I was saddened to read about it in the history books, but if the carp went the way of the passenger pigeon my response would be very different.

Most of the carp information shared today came from a Research Addendum done by Peter Sorenson. I would be glad to forward the report to you if you contact me at rall@frontiernet.net. Then you can know all you want to know about controlling the biggest mistake that has ever entered our Minnesota lakes and streams.

Tags: carp, scottrall, scott, rall