Cod and Climate Change

The key question for the Cod and Climate Change (CCC) programme is “how does climate variability affect the productivity and distribution of cod stocks?”. Cod (Gadus morhua) was chosen as the principal target species because its biology is well known and it is a major component of most North Atlantic ecosystems. Its abundance and distribution have been shown to be sensitive to environmental variability. A range of scientific disciplines and scales of investigation is applied, from the effects of small-scale turbulence on encounter between fish larvae and their prey, to large-scale effects of interdecadal changes in wind fields on circulation and transport of heat, plankton and young fish.

The processes by which physical forcing affects cod stocks are complex, but the effects of climatic variability can nevertheless be detected. For example, periods of low temperature are observed to result in stock declines 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 of cod (especially the early life history). They give grounds for believing that the question posed is not intractable and that it will be possible to predict major changes in cod distribution and productivity under different physical regimes. An obvious subject of concern is the likely impact of the rise in ocean temperature, which has occurred over the past fifteen years, on cod stocks close to their upper thermal limit.

The GLOBEC approach provides a framework for nesting studies at different scales. In 1993 the CCC working group (GLOBEC Report No.4) identified common themes and methods which have since been applied in programmes at national and individual levels. It proposed and initiated comparative studies and cooperative research which has been carried at regional or international level, by workshops co-ordinated by ICES and GLOBEC.

For more information visit the ICES/GLOBEC CCC homepage