Diet overlap and consumption patterns suggest seasonal flux in the likelihood for exploitative competition among piscivorous fishes

–  Competition, both intraspecific and interspecific, among piscivorous fishes (predators) may be more pronounced in reservoirs because of the artificial nature of these systems and the continuous anthropogenic influences that may not allow natural processes to regulate their densities. Most studies attempting to measure the extent of competition are based on predator–prey balance indices that are annual snapshots and do not account for seasonal changes. We sought to identify times during the year when intra- and interspecific exploitative competition for prey was most likely among dominant predators in a large reservoir of the south-eastern United States. The possibility of interspecific competition was measured by examining the seasonal extent of diet overlap based on samples of stomach contents. The likelihood or severity of this competition was indexed by how well predators met their energy needs. We found predators were realising less of their energy requirements during spring and autumn, and diet analyses showed predators overlapped substantially in their use of prey during those seasons. Thus, exploitative competition was most likely or severe during spring and autumn; furthermore, this competition had the potential to be interspecific as evidenced by resource overlap. Resumen 1. La competicion intra- e inter-especifica entre peces piscivoros (i.e., predadores) puede ser mas pronunciada en embalses dada la naturaleza artificial de estos sistemas y la continua influencia antropogenica que pueden no permitir que los procesos naturales regulen sus densidades. La mayor parte de los estudios que han intentado medir esta competicion se basan en indices de balance predador-presa que solo representan imagenes anuales y no incluyen cambios estacionales. Buscamos identificar los momentos del ano en los que la competicion intra- e inter-especifica por las presas es mas probable entre los predadores dominantes de un embalse de grandes dimensiones del sur-este de los Estados Unidos. La posibilidad de competicion inter-especifica fue medida examinando el solapamiento alimenticio estacional basado en muestreos de contenidos estomacales. La probabilidad o severidad de esta competicion fue cuantificada sobre el nivel en el que los predadores satisficieron sus demandas energeticas. 2. Encontramos que los predadores realizaron menos sus demandas energeticas durante la primavera y el otono y los analisis de las dietas mostraron que los predadores solaparon substancialmente el uso de las presas durante estas dos estaciones. Asi, la competicion es mas probable o mas severa durante la primavera y el otono. Ademas, esta competicion tuvo el potencial de ser inter-especifica como lo puso de manifiesto el solapamiento en el uso de los recursos