Lake Michigan Bythotrephes prey consumption estimates for 1994–2003 using a temperature and size corrected bioenergetic model

Bythotrephes were collected on a regular basis at a 110 m deep reference station in Lake Michigan over a 10-year period 1994–2003. The measured population structure in conjunction with an updated bioenergetic model was used to estimate daily predation demands by Bythotrephes on the zooplankton community. The bioenergetic model incorporated the effect of temperature on growth and respiration and used a scalable size structure to adjust for a dynamic range in size across the season. A general linear model was developed to apply the bioenergetic results to routinely collected field data for estimating predation needs. Daily population consumption needs were estimated to be approximately equal to Bythotrephes standing biomass but varied as a function of water temperature and percent instar composition. At a temperature of 18 °C the predation needs of the population were equal to the population biomass. At warmer temperatures (22–24 °C) the daily needs were up to 35% above the population biomass. Within and across years the population was variable, while trend lines from the long-term data indicated biomass and predation needs had an initial peak in mid-August followed by a plateau period with a seasonal high peak mid-October. A decrease in the midseason long-term average size structure suggests that Bythotrephes may experience prey limitation during this time period of the year. Over the course of the 10-year period population cycles and peak biomass were fairly stable with no indication of a change in predation needs.