Range expansion of the western tubenose goby (Proterorhinus semilunaris Heckel, 1837) in eastern Lake Ontario and the upper St. Lawrence River

The western tubenose goby (Proterorhinus semilunaris) has been documented in the Great Lakes basin since the 1990s, when it was introduced to the system via the discharge of ballast water originating in the Ponto-Caspian region of eastern Europe. The first report of this species in the eastern Lake Ontario-St. Lawrence River Basin occurred in 2011, outside of Kingston, Ontario, but beginning in 2016 it has consistently appeared in annual ichthyological surveys in the Thousand Islands region of the upper St. Lawrence River. While these fish have not been detected in great numbers, their presence marks an expanding eastern invasion front into the St. Lawrence River, which could have ecological implications systemwide. Both active adult movement and passive downstream drift of larval tubenose goby coupled with introduction of this species via domestic ballast water discharge within the Great Lakes could be providing a secondary invasion route along the St. Lawrence Seaway.