Freshwater Solutions concluded that its assessment of the three lakes in northern Michigan definitely showed that migrating ducks, previously though to be inconsequential, were part of the problem. It’s still unclear to what degree. Also, Reimink found that a new snail species was contributing to SI. The SI life cycle in northern Michigan previously had been linked only to Common Mergansers and the T. stagnicola snail. Based on his findings last summer, Reimink concluded there was a new contributor, tiny SI-causing worms that used Helisoma snails and Canada geese as their hosts. FWS also found significantly more Helisoma snails in some northern Michigan lakes in 2019 than in 2018.
Meanwhile, Blankenspoor last summer attached tacking devices to the Common Mergansers he trapped to help locate trees where the hens make their nests with the though the holes they used could be blocked. While this method had technical success, it was not practical to implement as it was time consuming and expensive. In addition, SIS banded six female Common Mergansers and moved them to state-approved sites on Lake Michigan, Lake Huron and two impoundments. At least three of the hens dies and the signal was lost on a forth. One hen from Elk Lake was relocated to Suttons Bay and made its way back to Elk Lake. SIS determined that the hens stayed with their broods and moved many miles
from their relocation release sites.
Research on Elk and Skegemog Lakes in 2019 supported similar findings in 2018 – our lakes have some of the highest cercariae levels among northern Michigan lakes, even though we do not have large numbers of Common Mergansers. Some experts believe that only one or two broods of Common Mergansers could cause the numbers of SI infections on our lakes, while others believe the high cercariae numbers suggest other waterfowl are likely a vector.
Our 2019 research showed twice as many geese on our lakes in 2019 as 2019. This could be significant, considering Reimink’s findings linking a new snail and Canada geese to SI. In 2018, few Helisoma snails were in Elk and Skegemog, and none were infected with the SI larvae. In 2019, we did not collect snails, but the DNA analysis showed most of the cercariae coming from T. stagnicola snails (with Common Mergansers co-host) and Helisoma snails (Canada Geese co-host). Although more water samples showed cercariae from T. stagnicola, the count of the ‘worms in the water’ showed more from the Helisoma snail.