Are there really few piscivorous fishes in shallow estuarine habitats?

Shallow estuarine habitats throughout the world are recognised as valuable nursery grounds for juvenile fishes. It is often suggested that this is due , at least in part, to the occurrence of low numbers of piscivorous fishes in these habitats. This idea is not confined to particular habitat types, b ut has been used in reference to a range of habitats, including both vegeta ted and unvegetated areas. I evaluate the proposition that there are few pi scivorous fishes in shallow estuarine habitats, and suggest that the propos ition is ill-defined, with little unequivocal supporting or contradictory e vidence. To make any sense, the proposition must be evaluated relative to s ome other habitat, something often not addressed in previous studies. Addit ionally, including the full range of potentially piscivorous fishes is impo rtant if the role of predation is to be understood. Most studies have consi dered only large piscivorous fishes. This is unfortunate when the propositi on logically relates to an advantage for small juvenile fishes. There is co nsiderable evidence that, in addition to large piscivorous fishes, small ju venile fishes are extensively preyed upon both by juveniles of the large pi scivorous species and by a range of other small species that include a larg e component of fish in their diets. In addition, many of the prey species m ay, themselves, switch opportunistically to piscivorous feeding. Not only a re small piscivores numerous, but because of their size they are much more likely to access shallow waters than large piscivores. Even when the full r ange of piscivorous fishes are considered, it is not clear that the questio n of the abundance of piscivores in shallow waters should be the real focus of interest. Rather the crucial question is whether or not predator-induce d mortality is reduced in shallow estuarine habitats.