Evaluation of a methyl anthranilate-based bird repellent: toxicity to channel catfish Ictalurus punctatus and effect on great blue heron Ardea herodias feeding behavior

— We evaluated the methyl anthranilate‐based bird repellent, ReJeX‐iT TP‐40™ (TP‐40), for 1) its toxicity to channel catfish fingerlings (catfish), Ictalurus punctatus; 2) its effect on great blue heron (heron), Ardea herodias feeding behavior; 3) its efficacy in reducing heron predation on catfish; and 4) its effects on catfish growth. TP‐40 effectively maintained MA concentrations near the water's surface and below toxic levels for catfish in the water column. Water samples collected from 0.03 and 0.35 m below the surface of catfish rearing tanks (6,664 L) treated at application rates up to the equivalent of 200 kg/ha contained less than 5 ppm active ingredient, which is less than the no observable effect limit for catfish fry. No treatment‐related mortality of catfish was observed. Handling times of catfish fingerlings captured by herons from tubs treated with TP‐40 initially increased at application rates of 19.6 kgha or greater but decreased as a function of the number of catfish captured. Under simulated aquaculture conditions, TP‐40 did not affect the number of catfish eaten by herons from ponds treated at surface application rates of 0, 2, 22, and 220 kglha. TP‐40 had no affect on the time herons spent handling live or dead catfish. Ponds treated with TP‐40 at 220 kgha had a 46% increase in visibility (secchi disk method) and a 58% reduction in total suspended solids, suggesting the formulation was phytotoxic. TP‐40 did not affect fish growth. Analysis of individual behavior showed that herons may have habituated or become indifferent to the effects of the repellent after repeated exposure. Under the conditions of the study, herons did not maintain their body weight unless catfish were made available by disease or supplemental feeding, suggesting that herons may be inefficient at capturing healthy catfish. Surface applications of TP‐40 at 20 to 220 kg/ha were not effective in limiting predation by herons.