The Behavior of Adult American Shad (Alosa sapidissima) During Migration from Salt to Fresh Water as Observed by Ultrasonic Tracking Techniques

Abstract

Five of seven adult American shad (Alosa sapidissima), tracked continuously with ultrasonic transmitters in the lower estuary of the Connecticut River in 1968 during their spawning migration to fresh water, exhibited extensive meandering, ranging 24–53 hr in duration in the region of the saltwater–freshwater interface. The salinity in the Connecticut River is like a wedge; its daily position is dependent on upland discharge, and its hourly position is dependent on tidal activity. The fish were observed during all tidal conditions and at several discharge rates, and in all cases they remained near the leading edge of salt water during the meandering phase. This behavior pattern was not a result of handling nor was it a typical behavioral response to tidal cycle. It was concluded that the meandering observed in the region of the saltwater–freshwater interface was due to physiological adaptation of the fish to fresh water. Of the remaining two shad tagged, one proceeded directly upstream without meandering, and one moved downstream.