In September of 2015, FRNSA voluntarily closed the Menasha lock at the request of the Department of Natural Resources (DNR) to prevent the spread of an invasive fish, the round goby, which was discovered in Little Lake Butte des Morts. The goby is one of 192 invasive species found in Lake Michigan. The invasive species barrier at the Rapide Croche lock prevents transmission of any species from the Great Lakes into the lock system and eventually the Lake Winnebago watershed.
What do we know about round goby behavior?
Fish are uniquely sensitive to electrical currents because their muscle control is based on electrical impulses through their nervous system, and because they inhabit a conductive environment. Electrical barriers and guidance systems make use of this sensitivity.
We have reviewed results of scientific reports from researchers from the U.S. Geological Survey (USGS). Based published research, we know these characteristics of the round goby:
- The round goby is a bottom dweller where the current in an electronic barrier would be strongest.
- The velocity of the water in the navigation channel will affect the travel of the round goby. Part of the electronic barrier operations plan calls for flushing the lock daily prior to any lockages up or down the system.
How did the round goby get here?
The round goby is an invasive fish found in the Great Lakes. Several were found in Little Lake Butte des Morts in September of 2015. When they were discovered, the lock system was not open to the Great Lakes and there were no populations of round gobies in Lake Winnebago according to DNR testing. Additionally at the time of discovery, there were three miles of dry canal and three de-watered locks between Little Lake Butte des Morts and Kaukauna. It is important to remember the Fox River flows north and it is impossible for fish to travel from the bay of Green Bay to Lake Winnebago through the lock system due to the barrier at the Rapide Croche lock. The round goby were most likely introduced into the system as fishing bait, or on pleasure boats that were not adequately cleaned.
Is the Menasha lock the main entry point for round gobies?
No. Since the fish was found, there is a verified population in Little Lake Butte des Morts. Currently, there are more than 60 boat landings into Lake Winnebago that are not monitored, and each summer float planes land in Lake Winnebago thus increasing access points for invasive species.