Timing and Hydrological Conditions Associated with Bigheaded Carp Movement Past Navigation Dams on the Upper Mississippi River

Range expansion of invasive Silver and Bighead Carp (i.e., bigheaded carps) continues throughout the major river systems of the central United States.  The low-head navigation dams on these rivers might be restricting their range.  Further enhancing the restrictive properties of these locks and dams by adding deterrents or modifying operating parameters is being considered.  However, little is known about the environmental and operational factors that influence bigheaded carp passage through these structures.  To better understand these factors, we implanted transmitters into Silver and Bighead Carp in Navigation Pools 16-19 of the Upper Mississippi River.  Fish were tracked passively using a longitudinal array of hydrophones, along with active tracking by boat.  Over 98% of observed passage events occurred during April-July, which coincides with season, water temperatures and hydrology consistent with bigheaded carp spawning behavior.  This time period is typically characterized by peaks in annual discharge and associated “open river” conditions.  Movement of up to 270 km during 27 d was observed.  Our study demonstrates the relative ease by which bigheaded carps pass low-head navigation dams on the Upper Mississippi River during high discharge.  To effectively apply deterrent systems for bigheaded carps, managers will need to consider environmental and operational factors.