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

Kouta Miyamoto*, Theodore Edgar Squires, Hitoshi Araki

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)446-454
Number of pages9
JournalMarine and Freshwater Research
Issue number3
Publication statusPublished - 2018
Externally publishedYes

Bibliographical note

Funding Information:
The authors thank Kouji Mutou, Hidefumi Nakamura and Masaharu Murakami of the National Research Institute of Fisheries Science (NRIFS) for their help with the care of the fish. The authors also thank Tsutomu Takeda of Nikko Yumoto Visitor Center of Nikko National Park for his help with the identification of wildlife. The authors are grateful to Predrag Davidovic, Petar Ilic and Matthew A. Campbell for critically reading the manuscript and providing valuable comments. Tomoyuki Nakamura of the NRIFS helped us with valuable advice. This work was supported by a grant-in-aid from the Ministry of Agriculture, Forestry and Fisheries, Japan and JSPS KAKENHI Grant Number JP26292102.

Publisher Copyright:
© CSIRO 2018.

Other keywords

  • hatchery management
  • piscivorous water birds
  • predatorprey interaction
  • size-selective predation.


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