Do darters (Etheostoma sp.) in streams with introduced trout exhibit increased wariness?

Abstract

Introduced predators can negatively affect native prey species via either direct predation or through indirect effects such as behavioral changes or habitat shifts that lead to declines in growth, condition, and reproductive success. In freshwater habitats, salmonid fishes are one of the most common introduced predators worldwide. Most studies of effects of salmonids on native prey species have focused on direct predation, with fewer studies examining how behavior of prey is affected. We used a snorkeling protocol to examine whether introduction of rainbow (Oncorhyuchus mykiss) and brown (Salmo trutta) trout in streams was associated with increased wariness in two small prey fishes, darters in the genus Etheostoma. Wariness was measured as flight initiation distance (FID), the distance at which individuals flee from an approaching threat (snorkeler), for darters in four rivers with and four rivers without introduced trout. Darters in rivers with trout had longer FIDs, indicating that they were less tolerant of risk than darters in control rivers. Increased wariness could lead to darters decreasing activities associated with foraging and reproduction, which could have long-term negative effects on populations of these prey fishes.