Fish sampling: revealing the secrets below the St. Croix’s surface

Our correspondent recently spent a day learning exactly what swims in the St. Croix.




6 minute read

This smallmouth bass was one of two 18-inchers we caught that day.

The Department of Natural Resources crews who monitor the St. Croix River’s fish population have a beautiful office and a difficult job. I joined them on the upper river one hot day at the end of July for a stint as a sampler, wielding a net in the bow of a heavy-duty, flat-bottomed boat. Two poles jutting off the front like tentacles dangled cables into the water, stunning the fish with electricity — their muscles reflexively moving them toward the boat and within our reach.

Our captain John Frank was a man of few words who did his work diligently, making sure we covered as much of the river as possible, pushing the bow against the bank as I tried to snag a little northern pike, and frequently hanging the boat up on rocks in his effort to not miss a fish.

I’ve known my fellow netter Deb Sewell through her wonderful blog Sand Creek Almanac since 2005. A modern-day homesteader, she and her husband raise three kids in the wild country around Sandstone. We had met only once previously, but she knows of my love for the St. Croix and we’ve talked about me tagging along on a sampling adventure for the past couple years. This summer it came together, with no small thanks due to Deb for making it happen.

St. Croix River landing, morning sun

I met up with Deb and John, both fisheries specialists in the DNR’s Hinckley office, at a dusty landing upstream of Rush City. Out in the river, a couple guys in a small boat were wedged in some rocks, fishing sedately in the bright morning sun. Once our boat was in the water, we headed upstream. The first quarter-mile was glassy water, giving us plenty of time to enjoy the trip and study the thick green banks.

Then we came to a long, shallow riffle and started nosing our way up against the current, trying to find a channel. But there was none. John killed the motor and started pulling us. Soon we were all in the water, dragging the heavy craft toward deeper water above the rapids.

Since 1991, the Minnesota DNR has sampled the St. Croix every five years (it was supposed to happen last year but didn’t because of the state government shutdown). Three-person crews use the electro-shocker to collect as many fish as possible in several “stations,” stretches of river around a mile long, and then weigh and measure each one, recording its species and data, and taking scale samples from the game species (smallmouth, northern, etc.). The DNR does similar research on the Snake and Kettle Rivers and many other lakes and streams in the area.

Sampling is done to monitor the health of the fish community, track changes in populations, and to evaluate fishery management. Management is minimal on the St. Croix; there are special regulations for a few fish, but the river is not stocked. Its fish swim there purely of their own accord.

Shorthead Redhorse
Shorthead Redhorse, of which we caught 60 specimens.

Between the boat’s motor and the generator powering the shocker, sampling is noisy work. The contraption works best in shallow water, and I guess John figured the only way to find out how shallow we could go was to find out how shallow we could go, so the netting was interrupted frequently by hopping into the river and dragging and pushing the beast of a boat off the rocks. Then, back on the deck to pull more redhorse out of the water.

The sky was clear and the sun intense; it was sweaty work. Getting into the river to free the boat was refreshing. On the bow deck, with the electricity flowing into the water, we would stare at the surface. Sometimes there wouldn’t be a fish for a couple minutes, often times they would come in big bursts as we hit a school of redhorse. Their white bellies would flash first and then they would drift toward us.

One species liked to fly out of the water, flopping and splashing, perhaps a taste of what boating in Asian-carp infested waters is like. But these were all native species — the bottom-feeders perhaps not exciting fish but  indicators of clean, clear water. Of interest to anglers, we brought into the boat a couple 18″ smallmouth, a two-foot long northern pike, a couple eater-sized walleyes and many tiny bluegills.

I was hoping we would find a nice musky, but no such luck. In the middle of a bright, hot day, they were probably laying in the deep holes where our electricity couldn’t reach them. Deb said one of the river’s most enigmatic fish, the sturgeon, also rarely comes up in the surveys because they seek the deep water. The day after my trip, she sent me a photo of a 39″ sturgeon they caught at the next station downstream.

St. Croix River lake sturgeon fish
St. Croix River lake sturgeon

We went down the river twice, first on the Wisconsin side, then on the Minnesota. At the bottom of each stretch, we took inventory. Deb pulled each fish out of the tanks and laid it on a measuring board, identifying the species and calling out the length in centimeters, which John wrote on a clipboard. Then she deposited the fish in a five-gallon bucket. When there were five or six (of the same species), I would weigh the bucket with a hand-scale, calling out the weight, which John wrote on the clipboard. The game fish were all weighed individually on a digital scale, as soon as they quit flopping around.

Then, back in the river for them. Many of the fish remained stunned, laying in the shallows by the boat. Most would recover and swim off, a couple might become osprey or eagle food. I held one of the walleye until it revived and staggered away.

St. Croix River fish sampling smallmouth bass
Smallmouth bass

The day we were out, we caught 227 fish, representing 17 species: Golden, Shorthead, Greater, Silver, and River redhorse, Northern hogsucker, White sucker, Smallmouth bass, Bluegill, Northern pike, Rock bass, Walleye, yellow perch, burbot, black crappie, largemouth bass, and chestnut lamprey. They ranged from 15 gram bluegill young-of-the-year to seven or eight pound redhorse.

After we had been on the river for a few hours, a flotilla of canoes came around a bend upriver. When they reached us we were hung up on rocks and we stayed there and waited for them to pass. The paddlers went by in distraction, staring at our contraption quizzically, exchanging waves with us. Soon, they were gone again, riding the river around the next bend downstream.

That would usually be me. Letting the current carry the canoe, reading the river’s channels, looking long at whatever I passed. The sampling work was certainly a different way for me to experience the St. Croix opposed to the way I was familiar. It was not only that the river was a place for work rather than recreation, but also to see it as not just beauty but biology, not just a park but a laboratory.

When we had finished our work and the boat was loaded on its trailer, Deb and John drove off. I had a few more minutes before I needed to get going, and wanted to wash the dust and sunscreen and sweat off me, so I changed into shorts and swam in the river.

There was no one else around, just the sound of cicadas and a kingfisher on the banks and the river rolling over rocks. I let the current carry me 30 yards or so and then walked back up through the shallows, then repeated the journey. The water was cool and clear, and always pushing toward the sea.

Just around the next bend was a sandbar where I remembered stopping near the end of a day of canoeing with a group of friends last summer. We had swum and talked as the sun dropped toward the Minnesota bluffs. It was one of the finest moments of that whole summer, and the area was just as lovely this year. Blue and green and peaceful.This was the St. Croix River I have known: silence and water and sun. And all sorts of fish swimming beneath.

Upper St. Croix River


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4 responses to “Fish sampling: revealing the secrets below the St. Croix’s surface”

  1. Andy Avatar

    What a privileged opportunity! Thanks for sharing it.

    1. gregseitz Avatar

      Thanks! Felt very lucky indeed. Glad you enjoyed the story.

  2. Jfshiely Avatar

    Great story Greg!

  3. Wjlundquist Avatar

    Wow! ‘ Great read – I love the narrative. What a fun way to spend a summer day on the St. Croix; 227 fish temporarily detained, 17 species, and not a single fish was is peril. All were released to swim another day.


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Fish sampling: revealing the secrets below the St. Croix’s surface