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

No abstracts are to be cited without prior reference to the author.

As a stock close to the southern limit of the species’ range, the North Sea cod stock may be among those most affected by future climate change. Direct, as well as indirect effects of climate forcing may have the greatest effects on early life stages. We here present our examination of 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) on the presence/absence, as well as the non-zero abundance. For comparison, the egg distribution of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus) and plaice (Pleuronectes platessa) were examined likewise. 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 the settlement distribution. The habitat models had fairly good predictive power on the sub-decadal scale, but were found lacking on a longer time scale. Effects of climate change may be complex, giving some species and life stages within the same species an advantage, while others suffer detrimental effects.