Modeling growth and prey selection for larval cod (Gadus morhua) on Georges Bank

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An individual based model with a mechanistic foraging routine was used to simulate growth rates and prey selection on Georges Bank in May 1993 and 1994. Extensive observations of the zooplankton field, and the hydrography were used as forcing of the model, and the results were compared to field data and earlier modeling results. The observed growth rates were higher in 1993 compared to 1994 despite higher total biomass in the water column in 1994. The modeled growth rates were within the standard deviation of the observations but highest in 1994, with evidence of strong depth-dependence. Highest growth rates are found in the surface layer (upper 20 meters), and correspond to the region of highest abundance of observed larval cod. Prey selectivity was estimated using Chesson’s alpha index and compared to stomach content analyses. The results indicate that Pseudocalanus spp., Oithona spp. and Centropages spp. have the highest abundance and are within the size range that 7mm larvae could ingest based on the model. However, stomach content analyses reveal that Centropages were seldom found in the stomach of these larvae, suggesting that Centropages are not a preferred prey for these larvae.