Bioenergetic Evaluations of Factors Limiting Growth and Survival of Juvenile Salmonids in the Columbia River

Bioenergetics models can help develop a mechanistic understanding of factors affecting growth and survival of salmon and steelhead in the Columbia River Basin. Survival of anadromous salmonids has been strongly linked to size or growth at one or more critical periods during freshwater or early marine life.  Delayed mortality might be influenced by growth performance during earlier life stages.  Therefore, greater attention should be paid to the connectivity among life stages, and how growth performance, size, and physiological status affect survival probabilities in current and subsequent life stages.  My objective is to demonstrate how bioenergetics modeling can provide an effective framework for mechanistically examining factors affecting growth, quantifying temporal consumption demand, and evaluating competition between hatchery-wild conspecifics or among species.  Bioenergetics modeling can explicitly account for how temperature, feeding rate (a surrogate of food availability), energetic quality of the diet, and body size affect growth of a consumer.  Some brief opportunistic examples of bioenergetics model applications are offered to demonstrate how food web interactions can be quantified to address questions important to resource management and conservation. Bioenergetics modeling simulations indicated that 9 million hatchery and wild yearling Chinook salmon consumed an estimated 167 metric tons of prey over an average 14-d passage during peak migration between Lower Granite Dam and Bonneville Dam.  In another application, for every million juvenile American shad rearing in mainstem reservoirs, an estimated 25 MT of zooplankton (primarily Daphnia) was consumed during July-September in a cool year (1996), but increased to 52 MT over the same months in a warm year (1994).  This consumption demand coincides with peak rearing by sympatric subyearling Chinook salmon which exhibit considerable diet overlap with juvenile American shad in mainstem reservoirs.  Ideally, the combined consumption demand by juvenile American shad and subyearling Chinook salmon would be compared to the concurrent biomass or production of key prey like Daphnia to evaluate the potential importance of competition in regulating growth, and ultimately survival of subyearling Chinook salmon.  Improved understanding of mechanisms determining salmon production could be accomplished with minor changes in data collection, supplemented with directed research and monitoring.  Future restoration efforts could be evaluated in terms of how climate, food web and bioenergetic processes affect salmonid production by quantifying key environmental and ecological processes within a spatial-temporal, and life-stage specific framework.