Physiological Ecology of Juvenile Chinook Salmon (Oncorhynchus Tshawytscha) at the Southern End of Their Distribution, the San Francisco Estuary and Gulf of the Farallones, California

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"Juvenile chinook salmon,Oncorhynchus tshawytscha, from natal streams in California’s Central Valley demonstrated little estuarine dependency but grew rapidly once in coastal waters. We collected juvenile chinook salmon at locations spanning the San Francisco Estuary from the western side of the freshwater delta—at the con­fluence of the Sacramento and San Joa­quin Rivers—to the estuary exit at the Golden Gate and in the coastal waters of the Gulf of the Farallones. Juveniles spent about 40 d migrating through the estuary at an estimated rate of 1.6 km/d or faster during their migration season (May and June 1997) toward the ocean. Mean growth in length (0.18 mm/d) and weight (0.02 g/d) was insignificant in young chinook salmon while in the estuary, but estimated daily growth of 0.6 mm/d and 0.5 g/d in the ocean was rapid (P≤0.001). Condition (K factor) declined in the estuary, but improved markedly in ocean fish. Total body pro­tein, total lipid, triacylglycerols (TAG), polar lipids, cholesterol, and nonesteri­fied fatty acids concentrations did not change in juveniles in the estuary, but total lipid and TAG were depleted in ocean juveniles. As young chinook migrated from freshwater to the ocean, their prey changed progressively in importance from invertebrates to fish larvae. Once in coastal waters, juve­nile salmon appear to employ a strat­egy of rapid growth at the expense of energy reserves to increase survival potential. In 1997, environmental con­ditions did not impede development: freshwater discharge was above aver­ age and water temperatures were only slightly elevated, within the species’ tolerance. Data suggest that chinook salmon from California’s Central Valley have evolved a strong ecological pro­pensity for a ocean-type life history. But unlike populations in the Pacific Northwest, they show little estuarine dependency and proceed to the ocean to benefit from the upwelling-driven, biologically productive coastal waters."
salmon, biology, coastal resources