Response of native and introduced fishes to presumed antipredator secretions of Ozark hellbenders (Cryptobranchus alleganiensis bishopi)

Abstract

Like many amphibian populations around the globe, populations of hellbenders ( Cryptobranchus alleganiensis ) have declined substantially in the past three decades. The cause(s) of the decline are unknown, but one hypothesis is that predation pressure by non-native fishes has played a role. Hellbenders produce a milky, frothy secretion when stressed, and this secretion is assumed to serve an antipredator function. In this study, we tested whether the presence of the secretion would deter foraging activity by native and introduced fishes. We found little evidence to support an antipredator function for the secretion, at least at the relatively low concentrations that we used in our study. Two species, non-native brown trout ( Salmo trutta ) and native walleye ( Sander vitreus ), were stimulated to approach prey by the presence of the hellbender secretions. In a palatability experiment, rainbow trout rejected food pellets soaked in hellbender secretion more often than control pellets whereas brown trout did not. Although our data indicate that the presence of the hellbender secretion does not deter fish predators from approaching hellbenders, it is possible that the strong concentration that would be experienced during an actual predation event, particularly on larger individuals, might serve a deterrent function.