Diets and resource partitioning among three sympatric gurnards in Northeastern Tasmanian Waters, Australia

Abstract

Dietary niches can support the coexistence of closely related sympatric species in marine systems, which can lead to the presence of greater abundances of those species that can potentially support their fisheries or greater abundances for other fish species that prey upon those species. Dietary relationships for three species of gurnard (Family Triglidae) that occur together in the benthic coastal environment of northeastern Tasmania, Australia (Red Gurnard Chelidonichthys kumu, Grooved Gurnard Lepidotrigla modesta, and Roundsnout Gurnard Lepidotrigla mulhalli), were examined for the presence of such dietary niches. The species are either fishery-important (Red Gurnard) or provide prey (Grooved Gurnard and Roundsnout Gurnard) for fishery-important species (e.g., Platycephalidae and Zeidae). Based on stomach content analyses, all three gurnards were shown to be bottom-feeding carnivores that consumed mainly benthic crustaceans, particularly decapods and amphipods, with teleosts also being important in the diets of only the larger Red Gurnard. Nonmetric multidimensional scaling ordination and multivariate analyses based on volumetric contributions of different prey taxa to the stomach contents revealed significant differences in dietary composition among all three species, implying a partitioning of food resources. Size-related and temporal changes in dietary composition were each significant among the three gurnards, but there were no interactions between body size and time. Principal components analysis of head and mouth morphology demonstrated that mouth protrusiveness was the dominant morphological difference among species, which may in part account for the niche partitioning observed from the stomach content analysis. Given the important role of gurnards in benthic food webs, these relationships will improve the specification of ecosystem-based fisheries models and their ability to predict the effects of environmental and anthropogenic perturbations.