A metabolic life table exemplified by sockeye salmon

Abstract

AbstractA metabolic life table (MLT) is a combination of energy budget and life table that quantifies metabolism and life history over an entire life cycle. It provides a conceptual framework for integrating data on physiology, demography and ecology that are usually the subject of discipline- and taxon-specific studies.Our MLT for sockeye salmon revives John Brett’s classic data on metabolism, growth, survival and reproduction to provide a synthetic analysis of metabolic performance and its life history consequences.The MLT quantifies the energy budget of an average female over her life cycle. The early stages in fresh water have low rates of growth and mortality. Then juveniles enter the ocean, feed voraciously, grow rapidly, and accumulate a store of biomass; More than 98% of the total lifetime assimilation and growth occurs in the ocean. Maturing adults stop feeding, return to fresh water, expend stored body energy to fuel migration and reproduction, and leave a clutch of eggs and a depleted carcass.The MLT also quantifies the energetic contribution of salmon to freshwater and marine ecosystems. Salmon are very efficient: of the food energy in their zooplankton prey, 47% is expended on respiration to fuel activity, 23% is allocated to growth and reproduction to produce biomass, and 30% is excreted in feces. Although 96% of lifetime biomass production occurs in the ocean, about 29% is transported into fresh water in the bodies of maturing adults, where their carcasses and gametes provide an important “marine subsidy” to the energy and nutrient budgets of freshwater and terrestrial ecosystems.The MLT highlights some features of the salmon metabolism – variation in rates of assimilation, respiration and production with body size and temperature – that are qualitatively similar to other ectotherms and predictions of metabolic theory. But because of the unusual physiology, life history, ecosystem impacts and socio-economic importance of wild-caught salmon, reanalyzing Brett’s data in the context of a MLT has additional broad applications for basic and applied ecology.