Where to spawn and where to hatch - a comparison of early and late stage fish eggs in the North Sea

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Changing climate may shift environmental conditions out of the hitherto observed range, endangering the reliability of model predictions based on historical observations. The SUNFISH (Sustainable fisheries, climate change and the North Sea ecosystem) project aims to create a basis for evaluating effects of future climate change on the North Sea ecosystem. Part of this programme is to investigate the influence of hydrography on spawning and settling areas of North Sea cod (Gadus morhua). Hydrography influences the condition and distribution of spawned fish eggs and may, besides homing behaviour, determine where fish choose to spawn. This study compares hydrography and distributions of eggs and larvae of several commercially important fish species, in late winter 2004 and 2009, investigating potential biophysical linkages. Several areas of high spawning intensity were identified. The hydrography shows a corridor of dense water from the northern North Sea to the English Channel accompanied by a strong boundary between the dense water and water of lower density influenced by freshwater inflow. Peak densities of eggs and larvae were seen along this boundary, giving further support to the hypothesis that hydrographic fronts are important spawning sites for fish. The consequences of these linkages are discussed in relation to potential climatically induced changes in temperature and salinity fronts in the North Sea.