ACOUSTIC DETERRENTS DO NOT REDUCE BLACK DRUM PREDATION ON OYSTERS

Abstract

We studied the effectiveness of acoustic deterrents in limiting predation on Louisiana oyster leases by black drum Pogonias cromis. Three acoustic deterrents were used: (1) natural or synthesized alarm sounds; (2) synthesized, low frequency sound played over short time intervals and (3) mechanically produced sound. Fish locations were monitored in all approaches and feeding rates on oysters were recorded in approaches 1 and 3. Experiments in salt-water ponds indicated that alarm calls from males, or synthesized tapes (approach 1) did not depress fish feeding rates or cause fish to avoid transducers, in comparison with controls. Lower frequencies (<20 Hz, approach 2) displaced fish 8 m further from transducers (about 20% of the distance possible) relative to controls. Finally, a solar-powered hammer (approach 3) was designed as a more logistically feasible deterrent. Fish were weakly attracted (although control and experimental locations differed by only 5%). Because acoustic deterrents were either ineffective at displacing fish or lowering feeding rates on oysters, or required considerable electrical power to displace fish, we conclude that they are not practical to control losses of oysters on leases to black drum.