Modelling changes in the length-frequency distributions of fish larvae using field estimates of predator abundance and size distributions

The goal of this study is to determine if an individual-based size-dependen t model can realistically simulate changes in the length-frequency distribu tions of several species of fish larvae collected in Conception Bay in 1993 and 1994, using field estimations of growth and predator abundance. We fir st model the length-frequency distribution of field samples with the best p ossible estimates of mean growth rate. Then, we add predation mortality giv en the characteristics of the predator community observed during our survey s, which was composed of macrozooplankton and adult capelin. The larval fis h community is generally not affected by predation by macrozooplankton, as the average instantaneous mortality rate predicted by the model was 0.004 d ay(-1). Fish larvae appear to be more vulnerable to predation by the popula tion of adult capelin. We estimate that an abundance of adult capelin rangi ng between 0.2 and 1.0 individuals per 1000 m(-3) may have a substantial im pact on the larval fish community. The predictions of an individual-based m odel are directly related to the accuracy of estimates of the mean growth r ates of the larval fish cohorts. We find that it is difficult to differenti ate size-selective removal of individuals from random selection by analysin g changes of the length-frequency distributions of the larval fish communit y.