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Changes in structural connectivity as it can affect functional connectivity, the biological and behavioural responses of an organism, has been examined here over 2 contrasting years when the spatial distribution of larval and juvenile cod and their prey shifted from the flank to the crest on Georges Bank. New data on the gut contents of pelagic juvenile cod are compared with known prey distributions, potential growth and how climate warming can change connectivity in this region. Centropages spp. was the most important prey for pelagic juveniles, especially in June 1987 when they had high abundance on the crest and were dominant in the cod stomachs. In June 1986, copepod abundance was low where the juveniles were distributed along the flank. The potential growth of juvenile cod was greater in June 1987, consistent with the higher abundance of Centropages spp., and with higher recruitment survival, compared with June 1986. Annual changes in the spatial distribution of cod early life stages within the environment of cold or warm years can have different impacts on their growth and survival. Whereas the small copepods, Pseudocalanus spp., are primary prey for cod larvae and very abundant in cold years, larger copepods, Calanus finmarchicus and Centropages spp., are important prey for the pelagic juveniles and the latter species can have a high impact in warm years on the crest. The different spatial structure during cold or warm years provides an explanation why different year classes respond differently to environmental change. Depending on the presence or absence of specific prey, the functional connectivity response changes pathways that determine the growth and survival of early life stages and ultimately a role in recruitment.

Understanding larval fish survival dynamics is essential to determining variability in future adult population structure. Realistic modeling of larval fish feeding ecology depends on incor- porating both the biotic and abiotic conditions that affect predator-prey interactions. We used an individual-based model (IBM) to test which variables drive Atlantic larval cod Gadus morhua feeding preferences. The IBM included a bioenergetics component that incorporated metabolic parameters and growth and a mechanistic prey selection component that depended on larval development and behavior, prey size and behavior, depth, light, and physical oceanographic conditions. We applied our model to Georges Bank and incorporated high-resolution field data on environmental conditions and prey abundance to analyze larval cod feeding ecology. Based on simulated selectivity indices, we found that cod prey selection was determined by differential encounter of prey due to the abundance of suitably sized prey, their visibility, and larval cod ability to capture these prey items. The model suggested that Pseudocalanus spp. were the dominant prey species for larval cod because of their abundance in the water column and their large image area. Centropages spp. were also modeled to be an important part of larval diet, but no copepodite stages of this taxon were found in gut samples. Lack of Centropages spp. in the gut samples indicated that they are more elusive in their behavior than Pseudocalanus spp. Overall our results suggest larval cod feeding ecology on Georges Bank is a consequence of the physical and biological conditions rather than active prey selection.