Redefining the piscivore assemblage of shallow estuarine nursery habitats

It is often suggested that there are few piscivorous fishes in shallow estuarine habitats worldwide, and consequently that these habitats are valuable as nurseries for juvenile fishes because they provide refuge from predation. Information on the dietary habits of predatory fishes from tropical estuaries remains limited to broad summaries that lack quantitative detail on the fish components of the diet. Consequently, it remains unclear which predators in shallow tropical estuarine nurseries target new recruits. To define the assemblage of piscivorous fishes relevant to the functioning of shallow water nurseries, we examined the diets of predatory fishes from shallow (< 1.5 m) sandy habitats in the lower reaches of 17 tropical estuaries over 6 yr. In total, 51 taxa from 21 families fed on fish, and the piscivore assemblage included many taxa and size classes that have been previously overlooked. Piscivores ranged in size from 15 to 755 mm and the majority of taxa were piscivorous to some degree from sizes well below 100 mm. All of the smaller piscivores (< 100 mm) mainly preyed on small new recruits, while only some of the larger piscivores did so. The taxonomic and functional diversity in the piscivore assemblage, and the fish community as a whole, highlights the complexity of the role of predation in the functioning of shallow tropical estuarine nurseries. Despite this complexity, it is apparent that predation has the potential to be a major structuring force on shallow water tropical estuarine fish communities.