Evidence of habitat fragmentation affecting fish movement between the Patos and Mirim coastal lagoons in southern Brazil

The communication between the Patos and Mirim lagoon systems occurs via a natural channel called Sao Goncalo. In 1977, a dam was built in this channel to prevent entrance of saline waters from Patos Lagoon estuary into the Mirim Lagoon. Our results showed an abrupt discontinuity in salinity and fish species distribution along the study sites. Sites below the dam showed salinity values higher than zero, whereas sites above had zero salinity values across all sampling periods. Marine and estuarine fishes (e.g., mullets Mugil platanus, M. curema, silversides Odontesthes argentinensis, Atherinella brasiliensis, sardine Brevoortia pectinata, and white croaker Micropogonias furnieri) were not captured above the dam. If these juvenile fishes could enter the Mirim lagoon in greater numbers, they probably would enhance catches in the artisanal fishery. We hypothesized that the Sao Goncalo dam acts as a barrier hindering the entrance of salinity water and fishes inside the Mirim Lagoon.