| 意見 |
Epipelagic (Ref. 58426). There are two forms, the anadromous form known as the sockeye and the landlocked form (with a much smaller maximum size) known as the kokanee (Ref. 27547). Upon emergence from gravel, fry at first tends to avoid light, hiding during the day and emerging at night (Ref. 27547). In some populations, sockeye fry go to the sea during their first summer but most spend one or two (rarely three or four) years in a lake before migrating (Ref. 30333). In a few streams of the Copper River drainage in Alaska, young sockeye stay in the stream (Ref. 27547). Once in the lake, the young spend a few weeks inshore, feeding largely on ostracods, cladocerans and insect larvae. The fish then become pelagic and move offshore, where they feed on plankton in the upper 20 m or so (Ref. 27547). Seaward migration follows with the young individuals first staying fairly close to shore, feeding mainly on zooplankton, but also on small fishes and insects (Ref. 30343, 30346). With growth, they head out to sea and fish become important in the diet (Ref. 27547). Kokanee are confined to lake-stream systems, and most of its life is spent in the lake (Ref. 27547). They feed mainly on plankton, but also take insects and bottom organisms (Ref. 1998). Kokanee, wherever they are native, have been derived from anadromous populations, and each kokanee population apparently has evolved independently from a particular sockeye run (Ref. 30338, 30339). Offspring of kokanee occasionally become anadromous, and sockeye offspring occasionally remain in freshwater (Ref. 27547). Lifespan of the kokanee varies from two to seven years in different stocks (Ref. 27547). |
