Graduate student: Darren Ward - now PhD Candidate at Dartmouth
Advisor: Ray Newman
Results of a previous investigation suggested that predation by sunfish (Lepomis spp.) may be an important factor limiting milfoil weevil populations when milfoil weevils are at low density (Sutter and Newman 1997). Some circumstantial evidence supports this: Cenaiko Lake, a lake in Minnesota with low sunfish density supports abundant milfoil weevils while Cedar Lake, a Minnesota lake with higher sunfish density has lower weevil density, despite weevil augmentations and abundant milfoil (Minnesota DNR lake survey reports for Cenaiko and Cedar).
Fish exclosure cages were set up in Cedar Lake to test to test whether reduced fish predation would benefit weevil populations. Cages were stocked with weevils in the spring and weevil populations were monitored throughout the summer. These experiments were somewhat complicated by fish invading the cages. However, there is evidence that weevil population growth is higher and weevil stocking is more successful in cages that exclude fish.
Otter Lake, Minnesota (lake survey report) suffered a severe fish kill during the winter of 2000-2001. Subsequently, in the summer of 2001 weevil densities in Otter were much higher than previous years and milfoil declined. We conducted a cage experiment using fish enclosures in Otter lake to asses the impact of increased fish predation on the dense weevil population there.
| |
|
| Underwater view of a fish exclosure at Cedar Lake | Underwater view of a fish enclosure at Otter Lake |
updated by Ray Newman 18 May 2006