Dear HLSIO Supporter,
The summer season has given way to the Holiday Season and we wanted to give you a wrap up of HLSIO 2024 activities. Let’s start with saying that in 2022 and 2023, the common merganser brood relocation program that we use to control Swimmers Itch on Higgins Lake was suspended by MI-DNR because of highly pathogenic avian influenza (HPAI). Fortunately, no common merganser broods appeared on Higgins Lake in 2022. In 2023, common merganser broods returned, with two broods observed. Since these broods were not relocated, it was predicted that SI metrics at Higgins Lake would increase in 2024. Waterfowl surveys of the entire shoreline of Higgins Lake were conducted by Swimmers Itch Solutions (SIS) on May 21, 2024, and again July 23, 2024. On May 21 there were a total of 20 Common mergansers found on Higgins Lake. On June 20 SIS captured 1 merganser brood (1 Hen and 9 ducklings) and relocated them to Lake Huron. On July 23, another bird survey was done and no common mergansers were found to be on the lake at that time. Because we found and relocated the ducklings prior to them becoming viable spreaders of the SI parasite, we expect SI cases in 2025 will most likely decrease.
On June 28, 2024 over 2000 snails were collected at ten different locations on Higgins Lake. Each snail was individually analyzed for avian schistosome infections. With two common merganser broods on the lake for the entirety of last summer, we had anticipated a slight uptick in snail infections in 2024. We did not find such an increase, likely due to snail infection being reduced so low in the past that a sample size of over 2000 snails is unable to provide anything of consequence. From the inception of Trap and Relocation work in 2015 the SIS website was able to accept information about SI cases throughout the summer. With the advent of the suspension of the program in 2022 we looked for another method of
monitoring SI cases. At that time the Higgins Lake Water Exposure study was initiated, and we have obtained data from swimmer’s experiences not only in 2022 but also in both 2023 and 2024. This data tells us when and where Swimmers Itch cases occur. We hope to develop patterns to analyze and help us determine how to better combat SI on Higgins Lake in the future.
Results of all monitoring show that cases on Higgins Lake increased a modest 2.34% in 2024, even though there were non-relocated birds on HL in the summer of 2023. In contrast, on Crystal Lake, SI cases increased from less than 1% to over 10% in 2023 and were further elevated in 2024. Additionally, most cases on Higgins Lake continue to be mild while some on Crystal Lake were quite severe. In 2023 and again in 2024 we sponsored research with the goal of knowing more precisely how quickly the parasites in newly infected ducklings became viable and began potentially infecting snails.
As a result:
- As expected, ducklings at the youngest ages (12, 15, 17, and 18 days old) were negative.
- Ducklings were first found infected at 3 week (21 days old), but producing parasites at a very minimum.
- The proportion of infected ducklings continues to increase with age, reaching peak parasite shedding at the 5 to 6 week period.
- All the oldest ducklings (52, 61, and 65 days old) were positive, and some were shedding very large numbers of parasite eggs, many times higher than younger ducklings and their mother hens.
- Second-year adults (who don’t yet breed but are present on Higgins Lake and other inland lakes in the summer) can have exceptionally high parasite egg counts, though there is variation. Three juvenile birds that were tested in 2024 were actually parasite free. Speculation was that possibly these birds came from relocation site environments where there were no snails present or possibly parasite production is greater between June 19 and July 1 and lessor between July 13 and July 24. It’s also possible that parasite outlook is somehow related to migration and after the migration period, production subsides, or perhaps parasite creation may be diminished as host immune systems mature. In any case, HLSIO intends to continue with the proven success of our relocation program and is already making plans to structure our program for next summer. Thanks to all our supporters for helping to keep Swimmers Itch to a minimum at Higgins Lake.
Your HLSIO Board,
Melanie Brown, Bill Carey, Phil Czech, Duncan Lawrence, Dale McDonald, John Ogren, Mike Purkey, Greg Semack