Gulf Sturgeon Response to a Tropical Storm Event

U.S. Geological Survey biologists have implanted Vemco® V16 sonic tags into anadromous Gulf sturgeon from the Suwannee River for various research projects.  During the summer of 2012, 49 sonic tagged sturgeon were present in the Suwannee River. On 24 June 2012, Tropical Storm Debby landed on Florida’s northwest coast. Approximately twenty inches of rainfall in the upper Suwannee River basin created rapid and extensive flood conditions.  Immediately following the storm, 90% of the tagged Gulf sturgeon were detected migrating downriver.  During the flood, the dissolved oxygen concentration dropped to critically low levels in the river.  As the dissolved oxygen concentration later improved, sturgeon moved back into the lower river, before migrating into the Gulf during the typical late fall timeframe.  Unusually early outmigration following early fall tropical storms has been observed; however, such behavior has not been documented during the mid-summer months.  This observation has generated a new hypothesis for why Gulf sturgeon might be exhibiting these storm related movements: rather than sturgeon utilizing floods as a low-energy migration method,  downriver migrations may be an evolutionary response to avoid hypoxic river conditions, which occasionally follow an event similar to Tropical Storm Debby.