Captive great blue heron predation on farmed channel catfish fingerlings

In a series of experiments, we examined feeding behavior of captive great b lue herons Ardea herodius and estimated their ability to affect commercial production of fingerling channel catfish Ictalurus punctatus. Specifically, we determined the following: (1) the biomass of channel catfish fingerling s necessary to maintain the body mass of wild-caught captive great blue her ons, (2) capture rates of captive great blue herons foraging on channel cat fish fingerlings, (3) evaluation of the losses of catfish fingerlings to he ron predation, and (4) the effects of selected catfish pond conditions on h eron capture rates and body mass changes. Consistent with previous studies, captive herons required approximately 300 g of live catfish daily to maint ain their body mass. Based on evaluation of seine haul indices and inventor y data, there was no significant difference (P > 0.05) in numbers of catfis h lost over time between control ponds in which herons were excluded and te st ponds where herons foraged freely, even though herons foraged on test po nds at a density almost twenty times greater than the average density repor ted on commercial facilities. Herons captured significantly fewer fish on c ontrol ponds than on ponds with "diseased" catfish (catfish temporarily dis abled by subcutaneous air injections) or "undesirable" fish (bluegills Lepo mis macrochirus; P = 0.0001 and 0.0003, respectively). Herons also lost sig nificantly (P = 0.0369) more body mass on control ponds than on "undesirabl e" fish ponds. Our findings suggest that unhealthy catfish or undesirable f ish are preferred prey for great blue herons. Heron inefficiency in preying on healthy catfish may limit their impact on fingerling catfish production , but additional studies are needed to substantiate these findings under ac tual field conditions.