Experimental evaluation of predation of stocked salmon by riparian wildlife: effects of prey size and predator behaviours

Abstract

Predation after release is one of the major concerns of hatchery fish conservation and propagation. However, the relationships between the size of hatchery fish, the predator species and their behaviours in natural environments are largely unknown. To understand these relationships, we conducted predation experiments in outdoor tanks and a seminatural stream with exposure to local predators. Masu salmon (Oncorhynchus masou) of two different size classes were used as experimental prey fish in the present study. Camera trap data showed that grey herons (Ardea cinerea) were the primary predator in the experimental system, and that most herons used 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 a significantly lower survival rate of larger salmon compared with smaller salmon. The 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 maximising the effectiveness of fish stocking.

Predation risk and resource abundance mediate foraging behaviour and intraspecific resource partitioning among consumers in dominance hierarchies

“…Moreover, fish responses to these predators were qualitatively similar to their responses to our decoy. While there is some evidence for sizebiased avian predation on salmonids (Miyamoto et al 2018), previous observations of visible injury to captured fish suggest that predation risk is not strongly size biased within the range of fish sizes in our experiment (55-162 mm fork length).…”

“…First, body size and social status likely covary with energetic state, which we did not explicitly account for and may be the ultimate driver of short-term behavioural responses (Gotceitas and Godin 1991). Second, we cannot completely rule out the possibility that perceived predation risk varied with body size (Miyamoto et al 2018). While these uncertainties cannot be resolved with the data at hand, they do not change any of the conclusions of our study so much as offer alternative mechanisms for them.…”

Predation risk and resource abundance mediate foraging behaviour and intraspecific resource partitioning among consumers in dominance hierarchies

“…Several opportunistic observations suggested fish responses to the decoy were qualitatively similar to their responses to these predators (S. Naman and T. Sato personal observation). While there is some evidence for size-biased avian predation on salmonids (Miyamoto et al 2018), previous observations of visible injury to captured fish suggest that predation risk is not strongly size biased within the range of fish sizes in our experiment (55-162 mm; T. Sato unpublished data).…”

Zooming in on mechanistic predator–prey ecology: Integrating camera traps with experimental methods to reveal the drivers of ecological interactions

“…Figures adapted from (a) Hunter (2009); (b) Suraci, Smith, et al (2019); (c) Haswell, Jones, Kusak, and Hayward (2018) and (d) Miyamoto et al. (2018; photo reproduced from Miyamoto et al., 2018 with permission from CSIRO Publishing)…”

“…To examine predator‐specific attraction to prey auditory and olfactory cues, Natusch, Lyons, and Shine (2017) simulated metallic starling Aplonis metallica vocalizations and scent at camera trap stations, demonstrating that starling predators were primarily attracted to scent cues. Predator diversity and consequences of predation on prey demography can also be assessed by stocking and monitoring a population of focal prey; camera traps deployed on outdoor fish tanks and semi‐natural streams identified the primary predator of Masu salmon, the influence of habitat and time of day on attack rates, the role of prey density on predator visitation, and the demographic class most impacted by predation (Miyamoto et al, 2018; Figure 2).…”