Climate regimes and water temperature changes in the Columbia River: bioenergetic implications for predators of juvenile salmon

Abstract

We examined how climatic regime shifts may have affected predation rateson juvenile Pacific salmonids (Oncorhynchus spp.) by northern squawfish(Ptychocheilus oregonensis, also called northern pikeminnow), smallmouthbass (Micropterus dolomieu), and walleye (Stizostedion vitreum) in theColumbia River. During 1933-1996, oceanic, coastal, and freshwaterindices of climate were highly correlated, and an index for the ColumbiaRiver Basin suggested that climate shifts may have occurred about 1946,1958, 1969, and 1977. Summer water temperature varied as much as 2degreesC between climate periods. We used a bioenergetics model fornorthern squawfish, the most important piscivore, to predict thatpredation on salmonids would have been 26-31% higher during two periodswith relatively warm spring-summer water temperatures (1933-1946,1978-1996) than during an extremely cold period (1947-1958). Predictedpredation rates of northern squawfish were 68-96% higher in the warmestyear compared with the coldest year. Predation rates of smallmouth bassand walleye on juvenile salmonids varied among climate periods similarto rates predicted for northern squawfish. Climatic effects need to beunderstood in both freshwater and nearshore marine habitats, sincegrowth rates of salmon populations are especially sensitive to mortalityduring early life stages.