Modelling the beginning and end of a planktonic life stage — the distribution of cod eggs and settled juveniles in the North Sea

The North Sea cod stock is close to the southern limit of the species’ range. Therefore, it might be vulnerable to future climate change. Direct as well as indirect effects of climate forcing may have the greatest effects on early life stages. Here we present a study on the distribution of cod (Gadus morhua) at the beginning and at the end of the planktonic life stage. The distribution of cod eggs
was modelled with generalized additive models (GAMs) for the resence/absence and for the nonzero abundance, using environmental as well as spatial covariates. For comparison, we also examined the egg distribution of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and plaice (Pleuronectes platessa). Findings indicated that in the egg stage, the
environment is more important for the probability of occurrence, while abundance is more under the control of spatial dependency. Modelling the potential habitat of newly settled 0‐group cod based on presence/absence alone, identified temperature, salinity, bottom depth, and geographic
position as the core descriptors of settlement distribution. The habitat models had good predictive power on the subdecadal scale, but were found lacking on a longer time‐scale. The results showed that the effects of the predicted climate change may be complex and may, even within the same species, be beneficial for one life stage and detrimental for another