Improving stocking success with predator recognition training

Authors: Matthew W. O’Neill, William Stewart

Year: 2012 (xliv)

Abstract

Predation by non-native fish may be the main source of mortality for bonytail and razorback suckers in the lower Colorado River. Hatchery-raised native fish are stocked naÁ¯ve to this risk and therefore may not survive their first encounter with a predator. We are developing a protocol to train large groups of hatchery-raised, native fish to recognize predators in an effort to improve post-stocking survival. We use the cypriniform alarm pheromone, known to be present in the skin of many cypriniform species, to train groups of hatchery-bred, predator-naÁ¯ve fish to recognize largemouth bass as dangerous. The alarm pheromone is collected by sacrificing and skinning a hatchery fish; the skin is blended with water to form a solution containing the alarm substance. Groups of hatchery fish are trained to recognize a predator by placing a bass into their tank and simultaneously adding the alarm pheromone. The bass is removed from the training tank after five minutes, and the hatchery fish are moved into a fresh tank. To document training success, 20 trained and 20 untrained fish (all previously pit-tagged so individuals can be identified) are placed into a concrete pond with four bass for 24 hours, and we compare percent survival of each group. Often a group of bonytail individuals, upon being introduced to the bare pond, immediately hide under the bass for cover. A second group of fish tends to school and keep their distance from the predators, but because we cannot determine which individuals are performing which behavior it is unknown if it is the trained animals that are avoiding the bass. Initial survival results, though not statistically significant, suggest that training will reduce predation compared to untrained fish. If predator avoidance training continues to show promise, further experiments will include introducing habitat, larger field tests, and scaling training to a hatchery production pond size.