Comparative Dietary Diversity and Trophic Ecology of Two Estuarine Mesopredators

Quantifying the trophic dynamics of mesopredators in coastal habitats is an essential precursor to understanding their role in linking multiple trophic levels. Traditional dietary analyses may miss key aspects of a species’ feeding ecology and may thus fail to identify trophic linkages between predators and economically important prey populations. We applied stomach content and stable isotope analyses to estimate diet and trophic dynamics and investigated intraspecific dietary diversity of bonnetheads (Sphyrna tiburo) and red drum (Sciaenops ocellatus). Both juvenile and adult bonnetheads and juvenile red drum had diets comprised mainly of crustaceans, notably portunid crabs and penaeid shrimp, with varying degrees of dietary and isotopic niche overlap. Juvenile and adult bonnetheads had high dietary and isotopic niche overlap, whereas the degree of overlap between bonnetheads and red drum varied. Our findings indicate that bonnetheads are dietary specialists whereas red drum are dietary generalists. Further analysis identified intraspecific variability in the diet of each species; adult bonnetheads had the highest prey diversity whereas red drum had the lowest. We show that dietary and isotopic niche overlap and intraspecific variation in diet exist among juvenile and adult bonnetheads and juvenile red drum, though to varying degrees. Our findings demonstrate the importance of fully examining the trophic ecology of species that share habitats and resources, both at individual and population levels.