Target strength of encaged Atlantic redfish (Sebastes spp.)

Redfish (Sehastes spp.) were caught at sea with feather hooks, kept alive i n sea cages for > 12 hours at 30 m depth, then transferred to cages at 10 m depth for another 12 h. Most fish survived this procedure in excellent con dition. A total of 16 fish of length 24.5-30 cm were placed one at a time i n an acoustically inert monofilament cage where target strength (TS) was me asured for two hours using a 38 kHz split-beam echo-sounder. An underwater video camera enabled continuous monitoring of fish and case. The best fit l ength based regression obtained from these data was TS=19 log [length (cm)] - 66.6. in the standard format: TS=20 log [length (cm)] - 68.1 (r(2)=0.18) . TS varied by less than 4 dB over a range of tilt angles from - 50 degrees to 70 degrees off dorsal aspect. (C) 2001 International Council for the Ex ploration of the Sea.