Early life stages of Northeast Arctic cod under various climate and demographic stock conditions

The Northeast Arctic cod (Gadus morhua) stock inhabits the Barents Sea and spawns along the Norwegian coast. We investigated the early life stages of this stock by combining in situ observations with statistical analysis and offline coupled models combining an ocean model, a nutrient-phytoplanktonzooplankton- detritus-model and an individual-based model for fish early life stages. The thesis’ main objective was to investigate how the demographic structure of the adults and environmental variables affect Northeast Arctic cod offspring distribution, growth and survival. The statistical analysis suggested that the demographic characteristics of the spawning stock affects larval abundance and that adult condition affects larval distribution. Larval abundance has a significant association with year-class abundance at age 3. One of the key findings of the coupled modelling results was that on average, there is a two-week delay from the peak timing of first-feeding cod larvae to the peak in prey availability. More larvae are food limited in warm years than in normal years. The positive effects of high temperature on growth, survival and ultimately recruitment are nonetheless larger than the negative effects of food limitation. Both early and late spawned larvae experience slower growth than individuals originating closer to the time of peak spawning in late March/early April. We find that survival is higher for scenarios when spawning is shifted southwards as compared to northerly shifts, and that in general mean survival is more dependent on shifts in spawning location than in spawning time. These findings reveal how and which mechanisms contribute the to varied distribution, growth and survival of Northeast Arctic cod early life stage from spawning until 1 year and to future recruitment.