By Ron Reimink, M.A. of Freshwater Solutions LLC, and Patrick Hanington Ph. D. of University of Alberta
We proposed to the Higgins Lake Foundation that a repeat assessment of parasites and hosts responsible for causing swimmer’s itch on Higgins Lake would help answer some important questions, information that would advance the science of these itch-causing parasites and be beneficial to lake associations in Michigan and beyond. In general, we hoped to discover why several years of summer resident common merganser removal appeared to be effective on Higgins Lake, while similar remediation efforts on other lakes in NW Michigan were not.
Freshwater Solutions (FWS), in collaboration with Dr. Patrick Hanington (University of Alberta), conducted a comprehensive survey of the schistosomes that are causative agents for swimmer’s itch on Higgins Lake in 2020. Included in the survey were biodiversity assessments of the invertebrate smail hosts and the parasites. Additionally, the magnitude of swimmer’s itch risk was assessed through qPCR analysis of swimmer’s itch-causing cercariae in water samples.
Our data suggests that a dramatic decrease in lake-wide snail density from 2016 to 2020, along with Stagnicola emarginata dominating the snail host community, help explain why merganser management has been successful on Higgins Lake and not on other lakes we have studied. We suggest other factors may also have influenced success, such as harassing and killing of mergansers (as opposed to just trapping and relocating), the distance of Higgins Lake from a costal waterfowl flyway, and lack of itch-causing parasite diversity.
Thanks to the support of the Higgins Lake Foundation, this study will be useful for other lake associations across the Midwest when assessing whether merganser removal will be successful on their lake. We encourage other lake associations to evaluate and consider the snail community structure and relative abundance of Stagnicola emarginata; prevalence and abundance of other itch-causing schistosomes; legal ability and desire to harass and kill common mergansers (besides just trapping and relocating); proximity to spring and fall waterfowl migration routes; possible unintended consequences of removing top predators from their lake ecosystem; and the feasibility of long-term success.
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View the full report here: Swimmer’s Itch Assessment Research, Higgins Lake Foundation 2020 Final Report