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Experimental evaluation for predation of stocked salmon by riparian wildlife: the effects of prey size and predator behaviors
Predation after release is one of the major concerns of hatchery fish conservation and propagation. However, the relationship between the size of hatchery fish, the predator species, and their behaviors in natural environments is largely unknown. To understand these relationships, we conducted predation experiments in outdoor tanks and a semi-natural stream with exposure to local predators. Masu salmon (Oncorhynchus masou) of two different size classes were used as experimental prey fish in this experiment. Camera trap data showed that grey herons (Ardea cinerea) were the primary predator in the experimental system, and that most herons utilized shallow areas in the morning or evening while feeding. Increasing the density of stocked salmon led to increases in the number of occurrences of grey heron. More importantly, predation by grey herons resulted in the survival rate of larger salmon being significantly lower than that of the smaller salmon. Our results indicate that it is important to understand local predators, adjust the optimum body size of hatchery fish at release, and choose the appropriate stocking site and time of day for maximizing the effectiveness of fish stocking.
MF17215 Accepted 27 September 2017
© CSIRO 2017