Food Habits Growth And Production Of Juvenile Spring Chinook Salmon Oncorhynchus Tshawytscha Walbaum PDF Download

Temperature was elevated approximately 4° C in a model stream relative to an unheated, but otherwise similar control stream. The streams were located outdoors, received identical amounts of exchange water from a nearby creek, and followed natural diurnal and seasonal temperature cycles Juvenile spring chinook salmon (Oncorhynchus tshawytscha) were introduced into each stream and allowed to remain about 1 year until the following winter. Their production was measured tri-weekly and related to changes in temperature, food availability, and other environmental factors. Ancillary experiments utilizing water from the model streams measured changes in pre-feeding survival and weight and differences in growth efficiencies at various rations. Two year-classes of juvenile salmon were studied. Chinook production in the unheated control stream exceeded that in the heated stream. In 1972 total production was twofold greater and in 1973 it was about 30 percent higher. Elevated temperature lowered productivity of the heated stream by causing increased mortality of eggs and fry and reduced growth efficiencies of juveniles as food became less abundant. It also resulted in lower biomasses of food organisms, either because the experimental elevation directly affected survival and growth of benthic invertebrates or because increased siltation associated with heavier growths of filamentous algae made riffle substrate less suitable for immature stages of certain insects. Beneficial effects of increased temperature included protection from infection by a trematode parasite (Nanophyetus salmincola) and, possibly, increased tendencies of some invertebrates to enter the drift.