Report of the Working Group on Cod and Climate Change

The qucstiori being investigated by the Working Group - the effect of climate variability on cod stock fluctuations - is simply stated, but involves many different scientific disciplines and scales of investigation. These range from the effects of small-scale turbulence on encounter rates between fish larvae and their prey, to large-scale effects of interdecadal changes in windfields on circulation and transport of heat and young fish. In spite of the complexity of the processes by which variable physical forcing may affect cod stocks, the effects of climatic variability can be detected for several stocks. For example periods of low temperature arc observed to result in stock decline at the northern limits of cod distribution (Barents Sea, Greenland); particular hydrographic and wind conditions result in unusual transport of eggs and larvae (Iceland-Greenland) or flush out deoxygenated basins where cod spawn (Baltic). These examples combine empiricism, a growing understanding of ocean/climate variability and detailed knowledge of processes during the life history (mainly early life history) of cod. They give grounds for believing that the question is not intractable and that we may be able to predict at least the broad direction of changes in cod abundance under different physical regimes. The Global Ecosystem Dynamics (GLOBEC) approach (sec Section 3) provides a conceptual framework within which studies at different scales can be nested. It is obvious from the reports of work in progress or in planning (see Sectiori 4) that a great deal of research which is relevant to Cod and Climate Change is already underway, even though it w:is riot primarily designed with that iri mind (for example studies of copepod dynamics and cod recruitment). The challenge for this Working Group (see Section 2) was to identify themes and approaches which strengthen and facilitate the scientific programmes being followed at individual or national level and to propose and initiate work which can be carried out more effectively at regional or international level, within ICES and GLOBEC.