Antipredator Mechanisms of Hatchling Freshwater Turtles

Populations of hatchling turtles are assumed to be under intense predation pressure until the individuals reach a size where they can no longer be taken by gape-limited predatory fish. This assumption is based solely on the physical capability of adult fish to engulf hatchlings and their co-occurrence with turtles in many habitats. It would appear that opportunistic feeders would take advantage of an influx of hatchlings upon emergence from a nest. However, there are only incidental accounts (unpubl.) of hatchlings found in stomach contents of predatory freshwater fish. Apparently hatchlings possess an effective, but previously undetermined, antipredator mechanism. Using largemouth bass (Micropterus salmoides) as a model predator, the objective of this experiment was to identify the mechanism(s) (taste, morphology, or behavior) used by hatchling turtles to avoid predation. Six experimental food treatments (ground internal organs and meat, ground shell and skin, ground whole turtle, dead hatchlings, anesthetized hatchlings, and active hatchlings) from two turtle species, the redeared slider (Trachemys scripta) and painted turtle (Chrysemys picta), and one control (ground fish cubes) were randomly presented to individually housed bass. Fish ate all treatments except active hatchlings which were attacked but subsequently egested unharmed. We conclude that hatchling behavior (e.g., clawing, biting, etc., which may be harmful to the gill apparati or digestive tract of bass) provides defense against predation. Through the course of the experiment, bass also exhibited learned avoidance of hatchlings. These fish may be associating the bright plastral colors and patterns common in these hatchlings with the behavior of the turtle. This is the first reported case of the noxious aspect of aposematic prey being associated with a behavioral rather than a chemical or a morphological defense.