On the variation in dab Limanda limanda recruitment: a zoogeographic study

Geographical variation in dab Limanda limanda recruitment and the related demographic parameters of growth, fecundity and mortality were studied. Also investigated was the effect of seawater temperature on recruitment variability and O-group growth. While populations situated towards the western edge (British Atlantic coast) and centre (southern North Sea) of the geographical range experienced different climatic and biotic regimes they had the following similarities. (1) A negative correlation between temperature at the time of spawning and O-group abundance the following autumn. (2) No significantly different mortality rates for the first 3 months post-settlement. (3) Almost identical coefficients of variation in between-year O-group abundance as measured between October and December. They differed in the following ways. (1) Juvenile and adult growth rates were initially faster in the Irish Sea but maximum size was greater in the southern North Sea populations. (2) Size-specific fecundity was higher in the North Sea. (3) Total mortality over the first year of life was higher in the North Sea. It is argued that the available evidence points to events during the egg stage as critical for determining recruitment success and it is conjectured that pathogens could be determining the egg mortality rate.