Manipulating Shad to Enhance Sport Fisheries in North America: An Assessment

Abstract

Manipulating forage fish populations to enhance sport fisheries is a common management practice. Here we review the literature dealing with manipulations of gizzard shad Dorosoma cepedianum and threadfin shad D. petenense to assess whether or not this practice has been successful. Shad introduction has tended to enhance predators, such as white crappie Pomoxis annularis, black crappie P. nigromaculatus, and largemouth bass Micropterus salmoides, and negatively affect presumed competitors, such as bluegill Lepomis macrochirus. However, responses have not been consistent within a species: some studies document negative responses of predators or positive responses of competitors to shad introduction. Depending on the study, target species have experienced negative, neutral, and positive effects due to shad removal, making generalizations impossible. Inadequate statistical analyses coupled with problems with study design further complicated interpretation of these studies. In addition, because resident predators feeding on introduced prey constitute only a portion of the complex of interactions that occur in a lake, factors such as multiple trophic levels, ontogenetic shifts in diet and habitat, and spatial heterogeneity must be considered when attempts are made to predict the outcome of forage-fish manipulations.