Thursday, October 10, 2013

Harvest Time - Autumn Carp Removal

Justine Koch, U of MN, with one of the largest fish caught yet.  Could this fish be old enough to retire?!

October marks harvest season in many counties in Minnesota, including here in suburban Maplewood. The difference here is that the ‘crop’ is carp, and the harvest will breathe new life into our lakes.

Our farmers in this scenario are the U of MN Carp Research Team (see the keyword ‘carp’ in the right column for more articles). They have had great success recently harvesting thousands of pounds of carp using something called a box net enclosure. This type of enclosure requires a large 70ft by 70ft net to be submerged at a presumed carp hangout. The carp find and feast on bait corn that is placed on top of this net for days or even a week or more. When the U of MN crew determines that enough corn is disappearing fast enough, signifying the carp school has relaxed about the free meal, the cue is given to hoist the pulleys supporting the sides of the box net up to trap the carp. This has to be done in the early morning while the carp are positioned over the net, actively feeding on the corn.
The U of MN crew harvest the carp using an electrofishing boat in
the box net enclosure, now with the sides of the net above water.

It’s 4:30 a.m. on October 2nd and Justine Koch, Reid Swanson, Brett Miller, and Mary Headrick have parked the trucks on Keller Lake island in the darkness. Their early-morning actions must be stealthy in order to get the sides of the net above water without startling the fish. Once done, they must wait until the sun rises to safely harvest the fish from the large pool of water enclosed by the box net. At dawn, an electrofishing boat is used to stun the carp to the surface of the lake and a team works to net them into a boat. From there, each carp is individually assessed to see if they have fin clips, floy tags, pit tags, or radiotags. Any one of these would indicate the carp had been previously captured by the UMN team and could provide valuable information about the carp population. A subset of these fish are measured for length and fin clips are taken to further a genetic study determining what strains of carp are in the Phalen Chain and where they come from. 

Reid Swanson measures one of the largest carp caught by the U of MN research team.

Reid and Justine check each fish for signs of previous captures.

The netting was very successful. The team removed 446 carp for a total of about 3700 lbs from Keller Lake!

The box net was then moved to Gervais Lake where the team coordinated with a friendly lakeshore owner to use their property for the harvest. Another exciting catch, 227 carp totaling over 2,000 pounds were brought in with some of the largest carp we have caught to date. Three or more of the carp were over 900mm long. By comparison, one of the oldest fish previously caught and assessed during this research measured in the 800mm range and was in its 60s! Otoliths will be taken from these large fish to determine their age.

These fall nettings bring us closer to our goal of having a manageable carp population in District lakes. Many thanks to Justine, Reid, and their crew for the long, stinky, and heavy work this harvest season!


  1. Why would you remove such fish? 60 years old? Were all these fish killed or removed to a better home?

  2. We remove carp in order to improve water quality in District lakes. As carp feed, they uproot aquatic vegetation and stir up phosphorous-laden sediment from the lake bottom, which leads to turbid water and algal blooms. The harvested carp are euthanized and donated to the University of Minnesota for research purposes, and some are fed to animals at wildlife rehabilitation and nature centers.