Van Etten Lake Association and Oscoda Township began a two-year stocking program in June of 2000. Van Etten is a 1,409 acre lake located in Oscoda, MI. Sixty eight thousand (68,000) weevils were stocked in eight Eurasian watermilfoil (EWM) beds over the course of the project. Two monitoring sites were established to monitor the movement of the weevil population throughout the lake. Qualitative observations were made regarding lake condition and quantitative data was collected on plant community composition, plant health, and weevil density.
At the time of the initial survey and stocking in June of 2000, the EWM was very healthy and not flowering in any of the eight stocking sites. The monitoring sites (un-stocked areas) were dominated by healthy EWM, and these were flowering. The results of the first follow-up survey in August of 2000 indicated that weevils were found in most of the stocking sites. EWM in one stocking site had virtually disappeared, and thus no weevils were found. The remaining seven stocking sites consisted of unhealthy EWM that had mostly fallen to the lake bottom. All plants were brown and hard, with very few leaves or meristems and no flowers present on the stem. Significant larvae and adult damage was observed.
By the time of the early summer survey and stocking event in 2001, EWM in almost all of the 2000 stocking and both monitoring sites had disappeared. The stocking and monitoring sites that had not disappeared had very high weevil densities. These results indicated that overwintering was a success and the weevils had returned to the lake in large, healthy numbers. An additional 62,000 weevils were stocked in six new sites during June, 2001.
The 2001 follow-up survey conducted in August indicated that the weevils had severely damaged EWM througout the lake. Twelve of the fourteen stocking sites from 2000 and 2001 had virtually disappeared. The remaining stocking sites still had patches of EWM (heavily damaged by weevils), but most of the observed EWM had fallen out of the water column and was covered in algae and laying on the bottom of the lake. One 2001 monitoring site which was not stocked was the only site in the lake where abundant EWM could be found. Most of the EWM in this location was algae covered and heavily damaged by weevils. The 2001 follow-up survey also noted an overall increase of the native plant species, Chara and Eelgrass, were found during the follow-up survey but were not detected in previous sampling.
The stocking of weevils into Van Etten Lake between 2000 and 2001 resulted in severe damage to EWM beds throughout the lake. The weevils successfully overwintered and returned to the lake in large numbers and have established a thriving population throughout the lake. The MiddFoil® Project in Van Etten Lake was so successful that a planned third year of stocking was eliminated.
