Length Dynamics in Juvenile Coastal Skagerrak Cod: Effects of Biotic and Abiotic Processes

Individual growth and size distributions within populations are generally influenced by both biotic and abiotic factors. Positively skewed size distributions may arise as a result of any size-selective process, such as food scarcity or competition. While such patterns have been observed for a variety of terrestrial plant and animal species, size distribution has been less studied for marine fish in the natural environment. This we do in the present paper. In order to investigate the effect of density and environment on juvenile coastal cod (Gadus morhua L.), we assess the length distributions of fish caught at fixed locations along the southern Norwegian Skagerrak coast over the period 1919-1996. We demonstrate that most distributions are skewed to the right, suggesting that competition may influence these systems; such effects seem to be strongest for sheltered stations inside the fjords. Density dependence is inferred as skewness increases with increased density, and the average length decreases with increased density. The skewness, average length, and abundance of juvenile cod caught in the autumn are shown to be influenced by the meteorological conditions in the spring (i.e., during the larval period). Directional wind stress along the shore and toward the shore and high temperatures create favorable conditions for the development of cod larvae. The effects of local abiotic factors may be measured through the North Atlantic Oscillation (NAO) Index, a large-scale climatic proxy.