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The article reports on the research conducted by Francis K. Wiese and colleagues on management of predator-prey relationship of birds and salmonids in the Columbia River basin. It shows that predator-prey relationships are altered as a result of human activities. In Columbia River basin, piscivorous predators have been implicated in contributing to lack of recovery of several endangered anadromous salmonids and control systems are instituted against piscine and avian species. Researchers employed the use of bioenergetics approach to estimate the consumption of salmonid smolts by waterbirds. Studies reveal that smolts survival could be maximized by deterring birds from the river when smolts are present, allowing bird presence after the diet switch to act as a tool for predator control.

We investigated growth and mortality of age-0 northern squawfish during early rearing in shallow shoreline habitats. Larvae and juveniles (n = 22914) were collected by weekly seining at three sample sites in the upper John Day Reservoir, Columbia River, during June through early September 1994-1996. Using a length-based ageing method, it was estimated that the exponential growth rate (C) for a common growth stanza (10-28 mm standard length SL) was significantly higher in 1994 (G = 0.047) than in 1996 (G = 0.037). Growth rate in 1995 could not be estimated, but was probably intermediate between 1994 and 1996 based on mean standard lengths of fish collected at the end of each sampling season (46.3, 40.0, and 32.0 mm SL in 1994, 1995, and 1996, respectively). For many fish species, variations in early growth can influence survival through size-selective mortality processes. Consistent with this possibility, our estimates of instantaneous mortality rates (Z) demonstrated that larvae and juveniles had significantly higher mortality in 1996 than in 1994 (Z = 0.103 in 1994, versus Z = 0.138 in 1996). Enhanced growth and lower mortality in 1994 were associated with a number of interrelated environmental conditions - comparatively low flows and turbidities, abundant instream vegetative cover, and high near-shore water temperatures. [ABSTRACT FROM AUTHOR]