INDIVIDUAL-BASED MODEL OF YOUNG-OF-THE-YEAR STRIPED BASS POPULATION-DYNAMICS .1. MODEL DESCRIPTION AND BASE-LINE SIMULATIONS

An individual-based model of population dynamics of age-0 striped bass Morone saxatilis is described and model predictions are analyzed. The model begins with spawning and simulates the daily growth and mortali ty of the progeny from each egg clutch as the fish develop through the life stages of egg, yolk-sac larva, feeding larva, and juvenile durin g their first year of life in a single, well-mixed compartment. Day of spawning and development rates of eggs and yolk-sac larvae depend on temperature. Daily growth of feeding individuals is represented by a b ioenergetics equation, for which consumption is based on random encoun ters by individuals with different types of prey. Larvae feed on four zooplankton types and juveniles feed exclusively on size-classes of fo ur benthic types. Mortality of eggs and yolk-sac larvae has both tempe rature-dependent and constant terms; mortality of feeding larvae and j uveniles depends on an individual's weight and length. Most of the com putations in the simulation involve determining the daily number of ea ch prey type eaten by each striped bass. Model predictions of larval a nd juvenile densities, growth rates, and mortality rates were similar to values observed in the Potomac River. Larger mothers produce more a nd larger eggs, which lead to larger larvae at first feeding. Increasi ng first-feeding size from 5.0 to 5.5 mm caused a 4.5-fold increase in survival to age 1. Average growth rates during the first 15 d of feed ing for larvae that would survive to age 1 were about 0.1 mm/d higher than the average of all larvae. Juveniles in the model appeared to die at random because both the rate and the degree of size-selective mort ality decreased rapidly during the juvenile stage. The model represent s feeding in detail: additional model refinements and analyses should focus on incorporating behavioral and phenotypic differences among ind ividuals, spatial and temporal variability in temperature and prey, an d further model corroboration.