Applying Fish Bioenergetics Model to Lake Trout in the Rapidly Changing Lake Huron Food Web

We estimated consumption of prey by lake trout Salvelinus namaycush in the main basin of Lake Huron during 1984-2010 by using bioenergetics models coupled with estimated time series of lake trout age-specific abundance, mortality, size-at-age, diets, and other inputs.  Lake trout was the top native predator in the North America Great Lakes but was nearly extirpated by the early 1950s due to excessive mortality from sea lamprey Petromyzon marinus predation and fishery harvest.  In Lake Huron, lake trout rehabilitation efforts have occurred in the context of continuous and rapid changes in the food web.  The most recent dramatic food-web changes included collapses of the dominant open-water prey (alewives Alosa pseudoharengus) and predator (Chinook salmon Oncorhynchus tshawytscha) species.  For individual lake trout, those food-web changes generated time-varying biological parameters such as length-at-age, length-mass relations, maturity schedules, and energy density as functions of body mass.  For lake trout populations, those food-web changes along with a gradual increase in adult stock contributed to major changes in age of recruitment to fisheries. We analyzed lake trout diet changes over time based on lake trout size groups.  We obtained abundance-at-age estimates from statistical catch-at-age assessments.  We used AD model builder to couple the fish bioenergetics modeling with time-varying input parameters at both individual and population levels.  In addition to estimating consumption, we also examined temporal and spatial patterns in the proportion of maximum possible consumption, energy conversion efficiency, and production-to-biomass ratio at both individual and population levels.  We also discussed efforts to extend this approach to other predator species so as to quantify the total top-down influence in the rapidly changing Lake Huron food web.