Behavioral Responses of Anadromous Blueback Herring and American Shad to High-Frequency Sound, Flow, and a Wing Wall in St. Stephen Tailrace, South Carolina.

In March 1992, we used fixed-aspect hydroacoustics in St. Stephen tailrace to monitor responses of fishes mostly anadromous blueback herring and American shad to high-frequency 118 kHz sound, flow, and the north wing wall. A 118-kHz transducer was aimed 4.6 m below the end of the north wing wall from a location 20 m downstream and near the north bank. It was used to guide fish around the end of the wing wall, which was believed to be an impediment to the movement of fish to the fish lift on the north side of the tailrace. However, 5 days of sampling clearly revealed that the wall does not hinder the movement of fish around the end of the wall. Observations of fish behavior were made during generation limited to the two turbines on the south side of the tailrace. Over 80 percent of targets observed moving upstream against current encountered a 0.3- to 0.7-msec eddy and followed it around the end of the wall rather than entering the area behind the wing wall, on sound on and sound off days. The eddy moved from the north bank, 20 m below the end of the north wing wall, to and around the end of the wall, and back toward the fish lift and St. Stephen Dam. The mean percent passage around the north wall on days when 118-kHz sounds were transmitted 119 percent did not differ significantly from that observed on control days when no 118-kHz sounds were transmitted 83 percent. A conservative estimate of total passage would be about 1,314 fishhour, assuming we sampled all depths that contained fish the top 42 percent but only one-third of the width they might have passed through. Cast netting from the end of the north wing wall, occasionally At targets tracked with hydroacoustics, captured nine American shad, five blueback herring, and one mullet