Olfactory deterrents to black drum predation on oyster leases

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Black drum (Pogonias cromis) predation is a serious threat to oyster production on Louisiana leases, and leaseholders hypothesize that black drum carcasses suspended above leases deter predation. We conducted experiments under laboratory and field conditions to test whether the scent of dead con-specifics deterred black drum predation. Preliminary experiments indicated that fish >70 cm total length were effective predators, and oysters <70 g wet total weight were preferred, and we used these sizes in subsequent experiments. Salinity did not affect feeding rates. Experiments in 30,000 L raceways indicated that scent did not significantly lower feeding rates. Parametric analyses of factorial experiments on oyster leases at two sites in Barataria Bay, Louisiana, during the fall and spring (periods of the year when fish feeding is most intense), indicated that scent reduced feeding rates by 10% to 20%, but only at one site in one season. Nonparametric analyses corroborated seasonal differences indicated by parametric analyses, but not the scent effect. We therefore conclude that scent from dead con-specifics is not an effective control strategy under most conditions. Dredge hauls during experiments suggested mortalities to all predators ranging from 63.1% to 92.5% within the first 4 weeks after seeding. The relative mortalities to black drum, southern oyster drills (Stramonita haemastoma) or possibly Perkinsus murinus infections varied among sites, as did temporal patterns of mortality within and among seasons.

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Journal of Shellfish Research

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