Watershed District hopes to use data to track, reduce carp

Published 7:31 pm Thursday, July 5, 2018

Editor’s note: This is the last in a five-part series on carp management efforts in the area.


Before developing a longer-term carp management strategy, the Watershed District will be fishing for a bit more data.

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According to Shell Rock River Watershed District conservation technician Scott Christenson, this year’s work should give him enough information to make those decisions, and to tailor them to the specific lake in question.

“Ever since this project started, we’ve been working on it, but we’ve got a lot of data to collect before — before we can make our best informed decisions,” Christenson said.

So far, data collected from carp tagging done in 2016 has allowed him to draw some conclusions: The electric fish barriers are working, limiting the amount of common carp getting upstream into shallow areas to spawn. It has reduced recruitment enough that Christenson said he hasn’t been finding any fish 1 year old or younger in Fountain Lake — and “that’s phenomenal,” he said.

Still, the most recent biomass estimates for carp in Fountain Lake were high.

“The ecological tipping point is about 89 pounds per acre,” said WSB & Associates senior ecologist Tony Havranek. The Watershed District is working with St. Paul-based WSB to carry out this year’s carp management actions.

However, Havranek said it’s also ideal to keep that level a bit lower than the threshold, so there’s a little wiggle room in biodiversity’s favor. Havranek said as the population is reduced and the team keeps track of water quality and other metrics, they can deduce the right threshold at which to manage lakes in the Shell Rock River Watershed District.

According to a proposal written by Watershed District resource technician Courtney Phillips in partnership with Carp Solutions, a University of Minnesota start-up that develops carp management solutions and with whom the Watershed District worked for its 2016 carp-tagging project, the estimate for carp biomass in Fountain Lake was approximately 1,160 pounds per acre. That is 13 times the ecological tipping point cited by Havranek. For Albert Lea Lake, the biomass estimate was approximately 535 pounds per acre. These conclusions were reached after three days of electrofishing surveys and based on a catch rate per hour during the electrofishing surveys, Christenson said.

These estimates don’t sit right with Christenson.

“This year we’ll be doing, reevaluating that, because that seems substantially high (in Fountain Lake),” Christenson said. “In my mind, it should be the other way around.”


Albert Lea Lake

Compared to Fountain Lake, Albert Lea is shallower with less stratification — temperature differences — in the water. If Fountain Lake is a bowl, Christenson said, Albert Lea Lake is a frying pan: shallow, flat and with little structure.

According to Christenson, the district has been successful in limiting recruitment, or the introduction of new carp, in Fountain Lake through its use of fish barriers.

Not so with Albert Lea Lake.

“We believe that it’s a huge driver of carp recruitment in the district,” Christenson said of Albert Lea Lake. It warms up faster and has several shallow bays with cattail fringes attractive to spawning carp.

So far, Christenson said the district did do some radio tagging in Albert Lea Lake in 2016. Radio tags allow the district to track fish by finding their radio frequency, which can provide information on where the fish are aggregating. This information can then be used to coordinate their removal with commercial fishermen. There are plans to outfit more carp with radio tags this time around as well, but Albert Lea Lake is on the back burner. It may have a higher carp population — or so Christenson suspects — and higher recruitment, but it’s a lower priority than Fountain Lake. Part of this is because Fountain Lake is an important fishery, he said. But part of this is due to the dredging project currently underway on Fountain Lake.

“We fix what’s upstream first,” he said.

After the dredging project is complete, Christenson said he anticipates cleaner, cooler water coming into Albert Lea Lake from Fountain.

“That’s going to change a lot of what happens in Albert Lea Lake, so we’re just going to wait — wait until we figure out what exactly is some of the impacts of the dredging (in Fountain Lake) on Albert Lea Lake,” he said.

Still, what work WSB and the district are doing in Albert Lea Lake will help them prepare for future projects.

“We’re hoping by the end of this year we’ll have a decent enough guide in identifying these nursery sites to kind of put together a long-term strategy for both Fountain and Albert Lea,” Christenson said.


Transect surveys

This year, Christenson said WSB will be updating the carp biomass estimate for both lakes through transect surveys. Havranek said those transect surveys will be conducted when WSB returns in the fall.

“The ultimate goal is to be able to look at the entire watershed and know how many fish are in each lake, when do they move and where they move, and where are those pinch points or aggregation sites … so we’ll have a ton of data at our fingertips,” Havranek said.

The data can help the district identify the scale of the problem and figure out where to allocate its funding and focus its efforts.

In a transect survey, the team will drive a boat along the shore for a specified amount of time; 20 minutes, Christenson said, is a relatively standard amount of time for a transect survey. The start and end points mark the boundaries of the survey area to work in. Carp found within that area will be measured and aged, and information from that survey can be extrapolated to give a picture of what’s happening in the lake as a whole. Christenson said it can be beneficial to redo past survey sites.

“If you’re doing the exact same procedure in the exact same spot around the same time of year, then you can kind of get a picture of what’s going on in the lake,” he said.


A ripple effect

And, at the end of the day, that picture is why Havranek and the district undertook this year’s process of tagging and tracking common carp. It’s why, when they catch the fish, they put them back into the lake.

“We’re leveraging the few fish that we release to get even more data and get even more fish,” Havranek said.

Removals don’t work, he continued, if you don’t first figure out how big the problem is. Data collected through these processes helps expose the scope.

“The value of that is much more than just keeping a couple hundred carp,” he said.

Christenson said he’s hoping that value comes out in boosted gamefish species’ populations, growth rates and health. To that list, Havranek added increased water clarity and increased density of aquatic vegetation that becomes increased habitat for waterfowl and fish. It’s a ripple effect.

“If we’re successful, it’s really dramatic, the changes that you would potentially see in these basins,” Havranek said.

Read the first part of the series here.

Read the second part of the series here.

Read the third part of the series here.

Read the fourth part of the series here.

About Sarah Kocher

Sarah covers education and arts and culture for the Tribune.

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