Status and trends of the Asian clam (Corbicula fluminea) in the lower Fox River and Green Bay

In the upper Great Lakes region, survival and population growth of the non-indigenous Asian clam Corbicula fluminea has been limited by cold climates that cause severe overwinter mortality. At these northern latitudes, Asian clam populations are often limited to thermal refugia – particularly warmwater discharges from industrial facilities. Several such facilities exist in the lower Fox River in Green Bay. Asian clams were first documented in the lower Fox River in 1999 and were extensively surveyed near the river mouth in 2011, but the few individuals found were restricted to the warmwater discharge from the Pulliam Power Plant. We performed a follow-up survey during 2017 to re-assess the population status of Asian clams in the lower Fox River at four industrial discharges, including the Pulliam Power Plant. We found more widespread evidence of Asian clams throughout the lower Fox River than previous surveys, but only one live individual was captured. We suspect that the back-to-back severe winters of 2013–2014 and 2014–2015 caused widespread overwinter mortality. Our investigation highlights the significant challenges for establishment of Asian clam populations in the upper Great Lakes region, and provides an example of a potential invasive species struggling to establish a viable population in a hostile climate.