Hi. I would like to present some results of what we are doing for modeling larval cod growth and survival in two distinct ecosystems. This work is a collaboration with other known GLOBEC participants, and also people in Norway. Our main focus is to explore how temperature, light, and food abundance may control growth of larval cod differentially through the season, and how these properties may change between ecosystems.

Our two ecosystems of interests are the Georges Bank cod population and the Northeast Arctic cod stocks. They are locate at the latitudinal extremes of the North Atlantic, and are used here as examples of two systems that can be studied in order of understanding how the governing processes required to ensure high growth and survival are structured in each system. To understand this we rely on the use of mechanistic individual based models that consists of the major physical and biological processes that we know govern growth of larval cod

If we look at the number of recruits from the Northeast Arctic cod stock we notice how the numbers that survives between years differ significantly, And just with 4 years temporal difference we find the maximum and minimum of the recruits.

The same type of pattern can be seen for Georges Bank cod stock. Thre are large variations in number of recruits per year.

We know that most of eggs and  larval cod dies. And we also know that the ones that survives the first 5 months of their life, are the ones that we fish 3 years later. There fore to understand fisheries recruitment we can have to understand the underlying properties that control growth and survival though the first 5 months. Still, these processes may rely n the ecosystem that we are interested in and can be varying widely between ecosystems.

For example light, is of crucial importance to larval fish. They rely on light to find food. For the two ecosystems that we are interested in here, there is a strong seasonal variation of number of light hours per day available to feeding in the Barents Sea. The number of light hours changes from 12=24 hours per day. For the Georges Bank, the seasonal variation in number of lighthours are much more constant. These properties make it distinctly different two grow up in the Barents Sea or the Georges Bank.

All of these properties are modeled though the use of an individual based model. Based on the input of temperature, light, and prey availability, combined with a mechanistic model for early life history of co, we are able to capture the essence of an ecosystem and how the larvae is able to survive in this ecosystem.

This approach was done in a recently submitted paper where we varied light , temperature, and prey abundance through the day for newly hatched larval cod in Lofoten. This made it possible to estimate growth as a  function of time of the year,

What we also did was to estimate the average temperature for the period 1995-1999 and then calculate the averaged growth for various levels of prey abundance. We then could relate yearly growth to the average growth rate and see how the growth anomalies varies between years. In this plot it is quite clear that 1999 is striking is a year of high growth rate, given high prey abundance, and this also fits well with observed values. Still, we need to compare these results with observed values of RNA:DNA.