Effects of Common Carp on Wild Rice Survival and Growth

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Aquatic Invasive Species (AIS): Common carp (Cyprinus carpio)
Project Location: Northwest Wisconsin (Burnett County)
Project Start Date: 04/2010
Expected Timeframe/Duration: ongoing
Sponsoring Organization: St. Croix Chippewa Indians of Wisconsin
Web Links: http://www.freshwatersci.com/fw_projects.html
Primary Contact: James A. Johnson; Aquatic Ecologist
Freshwater Scientific Services, LLC

Secondary Contact: Tony Havranek; Water Resources Manager
Project Summary:


Project Summary:
Upper Clam Lake in Burnett County is a 490 hectare lake with a mean depth 2meters. It supported large beds of dense wild rice prior to 2006 and was a major source of wild rice for harvesters and wildlife in the region. Beginning in 2006, rice beds in the lake began to decline substantially, and by 2009, only a few small, sparse, remnant stands of rice remained. Local managers suspected that carp may have played a role in the decline of rice. In 2010, we conducted a carp exclosure plot study in the lake to determine whether rice could survive and grow to maturity in the absence of direct carp effects (grazing or uprooting of rice). In the spring of 2010, we installed 4 plots (2 open and 2 fenced) in three locations of the lake and seeded one of each plot type. We then monitored rice survival and growth in all 12 plots in June and again in August. Results of the study clearly showed that direct carp effects were a major factor that had led to the decline in rice.
In the spring of 2011 and 2012, we installed nets to isolate a large bay from the main lake basin to exclude carp. By the fall of 2012, rice distribution and abundance increased substantially in the isolated bay.  The report is available through the link listed above.
In the winters of 2010-2011 and 2011-2012, the St. Croix Tribal Environmental Department hired a commercial fisherman to net carp under the ice.  Based upon mark-recapture studies, these winter nettings removed roughly one-third of the carp in the lake. Additional removals were scheduled for 2012-2013 with the goal of reducing carp abundance sufficiently to allow rice to reestablish in the main basin of Upper Clam Lake.
Ongoing research: 
We plan to net carp through the ice again this winter, followed by evaluation of rice survival in seeded open rice plots (carp not excluded) next spring to see if the carp population has been suppressed sufficiently to allow rice to survive in the lake. If we see high rice survival in the seeded plots, we will then plan to seed larger areas in the fall of 2015 to reestablish rice in the lake.