Comparison of the Diets of Hatchery and Wild Subyearling Chinook Salmon in the Columbia River Estuary
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Currently, Chinook salmon populations are declining (NRC, 1996). In the attempt to restore these populations, people have built hatcheries, which release fish into natural habitats (NRC, 1996; Olla et al., 1998). Ideally, this influx of fish should take pressures off of wild populations, enabling them to recover. However, this solution may actually be responsible for worsening their decline (NRC, 1996; Daly et al., 2011). The purpose of this study was to examine stomach fullness and contents of wild and hatchery subyearling Chinook salmon of two stocks. If the wild and hatchery salmon diets were similar, there would be potential for competition, which may result in further decline of wild populations. In general, the results showed that the diets of hatchery and wild salmon were very similar, with only a couple of significant differences in prey items consumed. However, the diets of fish significantly differed between years and between months, which may have resulted from varying environmental factors. The overall similarities between diets of hatchery and wild salmon may point to competition for food. This is important to consider when managing the number of hatchery fish released, so that both wild and hatchery fish have enough to eat in the estuary.