Abstract: An acoustic device for eliciting either attraction or repulsion behavioral responses in fish comprises a water tight enclosure having a radiating surface rigidly supported in one end thereof. Drive means for the radiating surface are provided with the capability of causing the radiating surface to vibrate at its resonant frequencies so that an acoustic signal is generated capable of a peak sound pressure level of at least 0.5 kPa (0 to peak) at a distance of 3 meters from the radiating surface. The signal generated has one fundamental frequency component in the range 20 to 1000 Hz and a plurality of resonant and harmonic frequencies associated with said fundamental frequency. The drive means, radiating surface and enclosure coact to generate an acoustic signal having characteristics such as resonant frequencies, peak pressures and temporal patterns which may be selectively optimized to produce the desired behavioral response.

Abstract: An offshore intake structure for a water cooling system having an intake shaft communicating with a lake or like reservoir comprises a well excavated in the bed of the lake having an opening communicating with the intake shaft. The well is covered by a submarine roof structure having a perforate outer region defining an inlet to the well and an imperforate inner region which extends over the intake shaft opening and radially outwards therefrom so as to define with the well bottom a horizontal flow passage extending inwards to the intake shaft. The construction is such as to permit an adequate intake flow while keeping the intake velocity below the limit at which fish would be entrained.