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The effects of experience on the acquisition of food by juvenile chum salmon, Oncorphynchus Keta, in a tidal creek of the Squamish River Estuary, B.C. Levy, David Alan


The feeding behaviour of juvenile chum salmon, Oncorhynchus keta, was analysed using a combination laboratory and field technique. The effects of experience with a single prey type were simulated by feeding animals in the laboratory with one of the following food types - the amphipod Anisogammarus confervicolus, the mysid Heomysis mercedis, or Oregon Moist Fish Pellets. After 30 days of laboratory experience, the experimental animals were marked and released into an intertidal creek of the Squamish River estuary, and subsequently recaptured. Analysis of the stomach contents of introduced fish showed that the proportion of Neomysis in mysid-conditioned fish was greater than the proportion of Neomysis in both the other experimental groups and naturally occurring chum juveniles in the tidal creek. In contrast, there was no difference in the proportion of Anisogammarus in the diet of amphipod-conditioned fish compared to the other experimental groups. Only very few amphipods were acquired by experimental animals compared to naturally occurring chum juveniles. Relative numbers of epibenthic invertebrates present in the water column were assessed by means of morning and evening plankton tows in the tidal creek close to the time of the experimental introductions. Anisogammarus was shown to undergo a diel vertical migration and was apparently unavailable to fish predators in the tidal creek at the time of the introductions. The lack of a measurable treatment effect in amphipod-conditioned fish was attributed to this factor. The proportion of Neomysis in the diet of experimental fish was different across all treatment groups on two consecutive introduction dates. The higher realized availability of Neomysis on the second introduction date indicated that differences in the relative abundance of various prey types occurred on a daily basis in the tidal creek.

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