A Successful Season of Carp Removal on Pleasant Lake

The Vadnais Lake Area Water Management Organization (VLAWMO) and Carp Solutions have successfully removed more than 21,000 pounds of invasive common carp during 2022.

The invasive common carp removal effort in Pleasant Lake began in 2019 with a survey to estimate the biomass of carp. Carp density was found to be 273 kg/ha, nearly 3 times the management threshold for water quality of 100 kg/ha. This estimate gave us a target for how many carp would need to be removed for improvement in the lake. Pleasant Lake is impaired for nutrients, and carp removal has the highest likelihood of improving water quality over many possible strategies that have been investigated.

Carp were tagged with passive transmitters during the survey effort to allow us to follow their movements when they swim by a stationary antenna. The antenna was placed between Deep and Wilkinson Lakes, with partnership and assistance from North Oaks Company. Movement of carp from Pleasant Lake to the permanent barrier at Wilkinson Lake was documented during 2020 and 2021 to identify timing of movements and peak migration time to prepare for a successful removal. The antenna and a remote camera were also in place in 2022 to alert Carp Solutions to the arrival of carp at a temporary barrier system that was put in place for the removal effort.

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Carp migrate out of Pleasant Lake in the spring as they attempt to move into Wilkinson Lake, which was a successful spawning and nursery area prior to placement of the permanent barrier by North Oaks Company in 1994. Carp eggs and young are easy prey for predator fish, including Bluegill sunfish that are especially effective at eating carp eggs. Carp move into shallow areas, like Wilkinson Lake, where predator fish are unlikely to survive through the winter because of low oxygen in the water. These areas offer protection for carp eggs and young. The permanent barrier at Wilkinson Lake has been extremely effective at severing this connection, as we’ve seen through a variety of methods over the past 3 years. The carp that we have found in Pleasant Lake are exclusively old, large adults. We have not found any young carp during surveys or removal.

The age of fish can be determined by counting rings on their ear bones (called otoliths), which is a process that is very similar to counting rings on a tree trunk. We wanted to know if carp in Pleasant Lake are likely older than the permanent barrier. We collected a few otoliths from harvested carp this spring. These fish were in their mid-40s and well predate the barrier that was put in 38 years ago.

A carp population of old fish without young being produced is good news for the removal effort because it means that fish that are removed are not likely to be replaced with a new round of baby carp each year. The average size carp in Pleasant Lake is 23 pounds, which is much larger than carp found in other lakes in the metro area.

This spring, as carp started arriving at the temporary barrier system, Carp Solutions had crews ready to go. They used backpack electroshocking units to stun the carp and scoop them up with nets. From there, the carp were loaded onto boats, humanely euthanized with clove oil, and transported for use as fertilizer for local farm fields.

Nearly 1,000 carp that weighed in at more than 21,000 pounds were removed over the course of the spring and summer.

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A follow-up survey will be done later this summer/early fall to determine what the current biomass estimate is in the lake. That number will tell us how much progress we’ve made and how far we have yet to go with carp removal. VLAWMO is planning to continue working with Carp Solutions on highly successful stream removals. A revised biomass estimate will be available on the VLAWMO website later this year.

VLAWMO is grateful to our many partners in the project including Carp Solutions, North Oaks Company(NOC), and St Paul Regional Water Services (SPRWS). We also appreciate the vision and partnership of North Oaks Home Owners’ Association in early phases of this project that have led to this removal effort.

Visit the Pleasant Lake Carp Removal project page for more information. 

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