Influence of Simulated Double-crested Cormorant, Phalacrocorax auritus, Predation on Multiple-batch Production of Channel Catfish,Ictalurus punctatus

The double-crested cormorant, Phalacrocorax auritus, is considered the primary depredating bird species on commercially produced channel catfish, Ictalurus punctatus, in the southeastern USA. We simulated different levels of cormorant predation on losses at harvest and economic effects on channel catfish production in a multiple-batch cropping system. We observed significant (P< 0.05) declines in catfish production at increasing levels of cormorant predation in this study. This decline was mitigated by increased individual growth of catfish at higher predation rates (i.e., lower catfish densities). This mitigating effect produced a non-linear relationship with total kg of catfish harvested per pond resulting in a non-linear incremental increase in breakeven price related to predation. Costs of production ($/kg) increased with increasing predation levels up to very high levels of predation with a cumulative maximum increase in breakeven price of $0.143/kg. These results indicate that losses at harvest due to cormorant predation occur immediately but are mitigated in part by compensatory growth of individual catfish. Losses due to cormorant predation in multi-batch systems can be considerable, but there is not a 1:1 relationship between losses and kg of catfish harvested due to compensatory factors. Channel catfish, Ictalurus punctatus, (catfish) aquaculture is one of the largest dollar value finfish aquaculture industries in the USA (USDA NASS 2014). The majority of this production occurs in the southeastern USA and the delta region ofMississippi in particular (USDANASS 2014). The double-crested cormorant (Phalacrocorax auritus, cormorant) is abundant in the region and is considered the primary depredating bird species on commercially produced channel catfish (Glahn et al. 2000; Dorr et al. 2012a). These factors have resulted in significant concern over the potential economic losses to the catfish aquaculture industry attributable to cormorant. Consequently, there has been considerable effort to understand and manage cormorant depredation issues. 1 Correspondence to: [email protected] Most of the research effort to date on cormorant impacts to catfish aquaculture has focused on bioenergetics modeling, delta-wide population surveys, and extrapolation of these data to the industry in estimating potential losses (Stickley et al. 1992; Glahn and Brugger 1995; Glahn and Stickley 1995; Glahn et al. 1996; Dorr et al. 2012b). However, little information exists regarding impacts at the pond or farm level. Glahn and Dorr (2002) addressed this issue for single-batch production scenario (Tucker et al. 2004) with alternative prey being present. Although this study provided insights on the effects of cormorant predation and alternative prey, it does not reflect current practices in the aquaculture industry. Glahn et al. (2002) evaluated the effects of cormorant predation at different levels by adapting research pond production data and modeling observed mortalities for multiple-batch cropping systems (see © Copyright by the World Aquaculture Society 2015