Innate Predator Recognition and the Problem of Introduced Trout

Innate predator recognition typically only occurs when there is an evolutionary history between predator and prey. Predator introductions thus can pose a substantial threat to native fauna that rely heavily on inherent identification of predators. In permanent aquatic habitats prey often encounter a variety of predatory and non-predatory fish species, and the ability to distinguish between the two is essential to avoid wasted time and energy spent in unnecessary antipredatory efforts. Here, we present a study evaluating the ability of lab-reared larvae of an endangered fully aquatic salamander (hellbenders: Cryptobranchus alleganiensis) to recognize chemical cues from native and introduced fish predators. We recorded responses of hellbender larvae to chemical stimuli from native and non-native predatory fishes, a non-predatory fish and a blank control. Eastern hellbender larvae (C. a. alleganiensis) significantly reduced activity in response to chemical stimuli from native predators (Micropterus salmoides, Micropterus dolomieu, Ambloplites rupestris, Sander vitreus, and Cottus carolinae), but responses to non-native rainbow (Oncorhynchus mykiss) and brown (Salmo trutta) trout were not significantly different from responses to the non-predatory control (redhorse sucker, Moxostoma spp.). Responses of larval Ozark hellbenders (C. a. bishopi) to brown trout were similar to that of the native fishes and different from the blank control, but responses to rainbow trout did not differ from the blank control. The generally weak responses of larval hellbenders to chemical cues from introduced predatory trout could lead to increased predation in the wild, which may have exacerbated the decline of hellbender populations.