Not to carp, but where’s my invasive gift?


A commercial angler stands with bins of caught carp — enough to fill a semi-truck. Removing these fish helps to improve and protect water quality in Big Green Lake. submitted photo

By Jennifer Fjelsted

June is Invasive Species Month in Wisconsin, which means later today you will likely rush to the store and pick out that perfect holiday card to send your friends and family.

Or not.

How does one celebrate Invasive Species Month, anyway? There are no specific colors, catchy tunes, or family traditions associated with it. There are no “Sorry your lake has milfoil,” “Happy zebra mussels anniversary!” or “Congratulations on your carp!” cards to send.

Instead, perhaps the best way to observe Invasive Species Month is to learn about what the problem is and how to do better at protecting Green Lake.

Adding a new invasive species to a lake’s ecological family does not result in congratulatory sentiments. Carp, for example, were the first invasive species introduced in Green Lake. In the 1800s, the U.S. Commission of Fish and Fisheries intentionally stocked carp in many Wisconsin lakes as a cheap food source. By 1894, as many as 35,000 carp had been stocked in Wisconsin waters.

The trouble with this short-sighted plan quickly multiplied. One female carp can produce 1 million eggs per year. Since carp are not native to Wisconsin lakes, they lack local predators to keep their population in check.

It is easy to see how the carp could (and did) get out of control (17,500 female carp x 1 million carp eggs = 17.5 billion baby carp each year).

Even if a portion of these more than 17 billion baby carp do not make it to adulthood, the result is a lot of carp causing exponentially worse problems for water quality.

Carp root around to gobble up aquatic vegetation and, in the process, stir up the lake bottom. This feeding behavior mucks up the water and destroys important spawning habitat for native fish species. It also pollutes the lake by re-suspending nutrients contained in the sediment—nutrients that serve as fertilizer for weed and algae growth.

We cannot travel back in time to warn the carp stockers of the 1800s that their actions would cause problems that we are still dealing with hundreds of years later. All we can do is annually remove a portion of the carp population to limit the damage to vulnerable areas of the lake and prevent history from repeating itself with the next invasive species.

Every year, the Green Lake Association, in partnership with the Green Lake Sanitary District, works to remove massive amounts of carp from the lake. This spring, commercial anglers removed 85,500 pounds of carp — enough to fill a semi-truck! Removing this many carp prevents an estimated 3,000 pounds of phosphorous from fueling 1.5 million pounds of weeds and algae in Green Lake.

Commercial anglers pull nets to bring in the carp from Green Lake. submitted photo

Coming full circle to the commission’s original intentions in the 1800s, the carp often are hauled away to fish factories and used as a food source.

While the government no longer stocks invasive species in Wisconsin, lakes, boats and anglers still sometimes do. One way is by dumping bait into a body of water and inadvertently introducing a new invasive species to a lake. Wisconsin law prohibits dumping bait into the water and, in some instances, prohibits reusing bait on another body of water within the same day (depending on how bait is handled).

Also of note, if you are bow fishing carp—thanks for getting rid of a few more!—but be sure to take your speared fish with you. Leaving them behind can result in a fine, not to mention the noxious smell of rotting carp left behind too.

Of course, carp are not the only invasive species in Green Lake. The Green Lake Association and our lake partners will continue to manage the ones we have.

In the meantime, there are plenty of offending species in nearby lakes that we do not have and we need to keep it that way. Until there are a line of greeting cards and jingles to remind you of invasive species, celebrate this month and our lake by following the invasive species prevention steps: Inspect equipment; Remove plants or animals; Drain all water.

Doing so will keep our lake healthy and clean for years to come.

That is something to celebrate.

Jennifer Fjelsted is the communication and project manager for the Green Lake Association, a local not-for-profit that works to improve water quality for Green Lake.

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