Randy Stowe, lakemanager@gmail.com

1. The MPOA dredging contractor is in the process of re-mobilizing this week, with the intent to resume dredging this coming weekend, weather permitting. Their current plan is to resume dredging in South Bay, concentrating on working the east shoreline first, to allow those lakefront landowners to install piers once dredging in that area has been completed. The intent is to have the dredging of South Bay, and any remaining dredging that can be done around O’Brien Shoals, completed as soon in the 2018 boating season as possible, after which the remaining dredging will be in West Bay. As a result, the dredging crew may be running longer shifts. As always, the MPOA will post updated information to the MPOA website www.wlmpoa.org as it becomes available.

2. On Saturday, April 21st, the Nippersink Watershed Association will conduct another workday, clearing invasive brush from a portion of the Merchant Creek stream corridor. This volunteer work is being done in advance of an upcoming IEPA Section 319 funded stream stabilization project to help minimize the significant amounts of sediment that this parcel has delivered to Wonder Lake over the past decades. Meet at 8 am on the north side of Wooded Shores Drive at Pleasant Drive. As always, volunteers are welcome.

3. There has been a lot of interest in the incredible number and variety of birds observed on the lake this early spring. The basic reason for this abundance is the Gizzard Shad, which recently has become very abundant in Wonder Lake. A number of questions have been raised about why the Shad seem to be dying off, creating a sushi bar for the birds. The most likely answer, as explained below, is quick changes in water temperature.

Gizzard Shad

Mortality caused by cold stress has been identified as a factor regulating the abundance of gizzard shad populations, particularly in waters near the northern edge of the species’ distribution where prolonged cold winters might almost eliminate them. Sudden cold spells causing water temperatures to drop several degrees in already cold water can cause massive kills.

In a study by Cornell University researchers, young-of-the-year gizzard shad were held in cages in Oneida Lake, New York, during the winter prior to ice-up.* Shad had low mortality in water above 46°F and mortality was high in water less than 39°F. Researchers also tested survival in cold rooms under controlled temperature treatments of 34°F, 36°F, and 39°F to simulate mid-winter conditions. First, shad were allowed to acclimate to 46°F, then the tank temperatures were reduced by about a half of a degree per day until the final test temperatures were reached.

Mortality was low during the acclimation period. A larger proportion of shad survived for longer periods in the 39°F tanks and mortality was highest in the coldest tanks.

Within each temperature treatment, small fish died faster. The researchers also observed that the average size of shad in field collections increased through winter, indicating higher cold tolerance of larger individuals. They conclude that cold stress and the inability to acclimate to decreasing temperatures, rather than starvation, are key factors in winter mortality.

These findings suggest that you can expect large shad winterkills when severe cold-fronts decrease water temperatures quickly in early winter before ice-up. Once lakes are covered in ice and buffered more from sudden changes in air temperatures, the severity of overwinter mortality should coincide with the duration of the ice-cover period.