Riparian groups seeking a permit to apply copper sulfate to their beachfront to control swimmer's itch should assess the effectiveness of their efforts. Counting parasites in water samples via qPCR for several days before treatment and for weeks after would offer valuable insight about the efficacy of their control efforts.
With cooperation from both the Lake Leelanau Lake Association and those riparians who annually apply copper sulfate as a molluscicide, we conducted pre- and post-analysis of water samples via qPCR to determine the degree and duration of application effectiveness.
While qPCR laboratory protocols are becoming well established, field collection techniques targeting the larvae that cause swimmer’s itch are in their infancy. Initial water sampling from 2016 showed real promise, yet lacked the scientific rigor needed to make definitive conclusions. Variables such as optimal volume of water per assay, collection time, collection depth, and the effect of wind/wave action needed to be determined. This research project aimed to discover optimal collection parameters and produce a simple protocol that will become the standard for lakes in Michigan and around the world.
Geolocators were placed on the leg band of 6 female mergansers we trapped with their broods in the summer of 2017. Geolocators record the date, time, and light intensity every five minutes, 24/7 for 3-5 years. Upon retrieval of the geolocators in 2018 and beyond, we hope to learn more about the reproductive natural history of common mergansers, which may help in our efforts to find and cover nest sites in the future.
Female mergansers exhibit predictable behavior when nest searching and egg-laying. This behavior can be observed, and the nests more easily located, once the first wave of migrants pass through after ice-out. Our work included watching merganser behavior during the spring and using cameras to look into potential nest sites. Both trail cam and geolocator data will help us learn about the many aspects of nesting behavior (i.e. optimal time of day, visits per day, etc.), which will facilitate nest finding in future years.
Years of experience have shown that a 90% reduction in parasite load, as measured by snail infection rate, does not translate into uniform swimmer’s itch reduction around the lake. Hot spots, where swimmer’s itch infection rates persist at high levels, still exist and create frustration for riparians, raising doubts about the effectiveness of control efforts. Spring or fall migrant mergansers undoubtedly transmit larval parasites to snails while visiting the lake, potentially aiding in creation of these hot spot areas.
FWS offers several new, innovative ideas to combat isolated hot spot areas. Testing began in mid-August of 2016 and showed some positive results. These new ideas were further tested to prove their level of effectiveness in 2017 and showed very promising results. Fortunately, qPCR offers a fast and precise way to measure success, allowing for modifications to be made and tested almost immediately. If continued research in 2018 proves equally successful, lake associations and individual riparians will have another powerful tool to reduce the incidence of swimmer’s itch in troublesome areas.
As we developed methodology for the qPCR analysis, we also needed to discover how many cercariae/25 liters are needed to create a swimmer's itch problem. By collecting, processing, and analyzing over 600 water samples and comparing to riparian surveys and anecdotal evidence we could establish a reliable severity index.